HIV Overview

What is a clinical trial?

A clinical trial is a research study in which people volunteer to help find answers to specific health questions. These studies are conducted according to a plan, called a protocol, which may include—

• New medicines or new combinations of medicines
• New medical devices or surgical procedures
• New, different ways to use an approved, existing medicine or device
• New ways to change behaviors to improve health

Clinical trials are conducted in several phases to determine whether new medical interventions are safe and effective in people. To get approval from the U.S. Food and Drug Administration (FDA), a new drug must go through three phases:

• Phase 1 Trial: Focuses on safety and dosage. A small group (typically 20–80 participants) receives the drug to determine safe dosage ranges and identify potential side effects.
• Phase 2 Trial: Evaluates effectiveness while continuing to monitor safety. Involves 100–300 participants with the condition being studied to determine how well the drug works and to make dosing changes if needed.
• Phase 3 Trial: Compares the new drug to existing treatments in a larger population (1,000–3,000 participants). Determines long-term effectiveness, safety, and side effects before seeking FDA approval.

Once a new drug is approved by the FDA, researchers often continue to track its safety in a Phase 4 Trial. This phase helps identify rare side effects, long-term outcomes, and how the drug performs in real-world settings.

What types of clinical trials are there?

The two main types of clinical trials are interventional trials and observational trials:

• An interventional study tests an intervention—a potential drug or treatment, medical device, or procedure—in people. Interventional studies are often designed in advance to directly evaluate the effects of new drugs or treatments on disease.
• An observational study does not directly test new treatments. Instead, researchers observe participants on an existing treatment plan and track health outcomes over time. Observational studies (also called epidemiologic studies) are mostly retrospective but can also follow participants over time.

What is an HIV and AIDS clinical trial?

HIV and AIDS clinical trials help researchers find better ways to prevent, detect, or treat HIV and AIDS. Every HIV medicine was first studied through a series of clinical trials.

Examples of HIV and AIDS clinical trials include—

• Studies of new medicines to prevent or treat HIV and AIDS
• Studies of vaccines to prevent or treat HIV
• Studies of medicines to treat infections related to HIV and AIDS, such as opportunistic infections

Can anyone participate in an HIV and AIDS clinical trial?

Participation in a clinical trial depends on the study. Some HIV and AIDS clinical trials enroll only people who have HIV, whereas other studies include people who do not have HIV.

Each HIV and AIDS clinical trial will also have specific criteria that can restrict who can participate in the study, including factors such as age, sex, pregnancy, HIV treatment history, or other medical conditions.

In addition, some clinical trials will only be available in a specific location. Even if someone meets the eligibility criteria, they may not be able to attend necessary visits to participate in the study.

What are the benefits of participating in an HIV and AIDS clinical trial?

Many people participate in HIV and AIDS clinical trials because they want to contribute to HIV and AIDS research. They may have HIV or know someone who has HIV.

People with HIV who participate in an HIV and AIDS clinical trial may benefit from new HIV medicines before they are widely available. For example, some ongoing clinical trials are studying long-acting HIV medicines that help reduce how often people with HIV have to take HIV medicines. See the HIVinfo Long-Acting HIV Medicine fact sheet for more information.

HIV medicines being studied in clinical trials are called investigational drugs. To learn more about investigational drugs, read the HIVinfo What is an Investigational HIV Drug? fact sheet or scan investigational HIV drugs using the Clinicalinfo Drug Database.

Another benefit of participating in an HIV and AIDS clinical trial is that participants can receive regular and careful medical care from a research team that includes doctors and other health professionals. Often, the medicines and medical care are free of charge during the study.

Sometimes people get paid for participating in a clinical trial. For example, they may receive money or a gift card. Participants may also be reimbursed for the cost of meals or transportation. 

Are HIV and AIDS clinical trials safe?

Researchers try to make HIV and AIDS clinical trials as safe as possible. However, volunteering to participate in a study testing an experimental HIV treatment can involve risks of varying degrees.

Most volunteers do not experience serious side effects; however, potential side effects that may be serious or even life-threatening can occur from the treatment being studied.

Before enrolling in a clinical trial, potential volunteers learn about the study in a process called informed consent. The process includes an explanation of the possible risks and benefits of participating in the study. Informed consent also covers how personal information will be shared during and after the study.

The FDA believes that obtaining a research participant's written informed consent is only part of the process. Once enrolled in a study, people continue to receive information about the study through the informed consent process. If a study intervention shows too much evidence of being dangerous, the study can also be terminated.

How can one find an HIV and AIDS clinical trial looking for volunteer participants?

There are several ways to find an HIV and AIDS clinical trial searching for volunteer participants:

• Use the “Find Studies” search feature on ClinicalTrials.gov to find HIV and AIDS studies looking for volunteer participants.
• Call an HIVinfo health information specialist at 1-800-448-0440 or email [email protected] to get support finding a clinical trial.
• Join ResearchMatch, which is a free, secure online tool that makes it easier for the public to become involved in clinical trials.

This fact sheet is based on information from the following sources:

From the National Institutes of Health (NIH):

• Are clinical studies for you?
• Clinical Trials: Information for Participants
• NIH Clinical Research Trials and You: The Basics

From the National Library of Medicine:

• Learn About Clinical Studies

Also see the HIV Source collection of HIV links and resources.

What is HIV and AIDS?

HIV stands for human immunodeficiency virus, which is the virus that causes HIV infection. The acronym “HIV” can refer to the virus or to HIV infection. 

AIDS stands for acquired immunodeficiency syndrome. AIDS is the most advanced stage of HIV infection.

HIV attacks and destroys the infection-fighting CD4 cells (CD4 T lymphocytes) of the immune system. The loss of CD4 cells makes it difficult for the body to fight off infections, illnesses, and certain cancers.

Without treatment, HIV can gradually destroy the immune system, and may cause a decline in health or progress to AIDS. This includes an increased likelihood of getting other infections like hepatitis, tuberculosis, and some sexually transmitted infections. 

With treatment, the body can prevent HIV from destroying CD4 cells, allowing the immune system to recover and protect against other infections.

See the HIVinfo The Stages of HIV Infection fact sheet for more information on how HIV progresses to AIDS.

How is HIV transmitted?

HIV can be transmitted through bodily fluids, including blood, semen (“cum”), pre-seminal fluid (“precum”), vaginal fluids, rectal fluids, and breastmilk. HIV can be transmitted through these fluids in the following ways—

Blood:

• Sharing needles or syringes for injecting drugs or tattooing
• Being exposed to the blood of a person with HIV through accidental needle sticks
• Sharing personal items that may have blood on them (such as razors or toothbrushes)
• Eating prechewed foods (in case of open sores or bleeding gums)

Semen, Preseminal Fluid, Vaginal Fluids, and Rectal Fluids:

• Having vaginal or anal sex
• Having oral sex (less likely, but can occur in rare cases)

When an infant gets HIV during pregnancy, childbirth, or breastfeeding, it is called perinatal transmission of HIV. For more information on perinatal transmission, read the HIVinfo Preventing Perinatal Transmission of HIV fact sheet.

You cannot get HIV by shaking hands or hugging a person who has HIV. You also cannot get HIV from contact with objects, such as dishes, toilet seats, or doorknobs, used by a person with HIV. HIV is not spread through the air or water or by mosquitoes, ticks, or other insects. 

Use the HIVinfo You Can Safely Share…With Someone With HIV infographic to spread this message.

What is the treatment for HIV?

Antiretroviral therapy (ART) is the use of HIV medicines to treat HIV. People on ART take a combination of HIV medicines (called an HIV treatment regimen) every day (pills) or on a schedule (injections). 

In many cases, oral medicines may be combined into a single pill or capsule instead of multiple pills. There are newer long-acting medicines given by injection every two weeks to six months that may be appropriate for some people with HIV. 

Although injectable HIV medicines are taken less often, they require an appointment to be administered by a health care provider. See the Long-Acting HIV Medicines fact sheet for more information.

ART is recommended for everyone who has HIV to prevent the virus from multiplying, which reduces the amount of HIV in the body (called the viral load). Having less HIV in the body protects the immune system and prevents HIV from advancing to AIDS. ART cannot cure HIV, but it can help people with HIV live long, healthy lives.

How can a person reduce the chances of transmitting HIV?

ART reduces the chances of HIV transmission. ART can reduce a person’s viral load to an undetectable level. An undetectable viral load means that the level of HIV in the blood is too low to be detected by a viral load test. 

People with HIV who maintain an undetectable viral load have no risk of transmitting HIV to their partners through sex. This is known as Undetectable = Untransmittable, or U=U.

HIV medicines taken during pregnancy, childbirth, and breastfeeding can also reduce the likelihood of perinatal HIV transmission. Evidence suggests that the odds of perinatal transmission are less than 1 percent when breastfeeding with an undetectable viral load.  

Feeding infants using properly prepared formula or pasteurized human donor milk from a milk bank can eliminate the chances of perinatal HIV transmission completely. Health care providers can help determine the best approach to infant feeding based on the likelihood that an infant will be exposed to HIV after pregnancy.

How can a person reduce the risk of getting HIV?

There are several ways to reduce the risk of getting HIV:

• Using condoms correctly with every sexual encounter, particularly with partners who have HIV with a detectable viral load or whose HIV status is unknown
• Avoiding needle sharing
• Choosing safer sex practices (such as limiting the number of sexual partners)

People who do not have HIV should talk to their health care provider about pre-exposure prophylaxis (PrEP) if they believe they are at risk of getting HIV. PrEP involves taking a specific HIV medicine on a routine schedule—daily for pills or by schedule for injections—before an HIV exposure. For more information, read the HIVinfo Pre-Exposure Prophylaxis (PrEP) fact sheet.

Post-exposure prophylaxis (PEP) can also reduce the chances of getting HIV. Unlike PrEP, PEP is taken within three days (72 hours) after an exposure. Read the HIVinfo Post-Exposure Prophylaxis (PEP) fact sheet for more information.

What are the symptoms of HIV and AIDS?

Within two to four weeks after infection with HIV (known as early or acute HIV infection), some people may have flu-like symptoms (such as fever or chills). The symptoms may last for a few days to several weeks.

Other possible symptoms of HIV include night sweats, muscle aches, sore throat, fatigue, swollen lymph nodes, headache, diarrhea, mouth ulcers, and skin rash. Having these symptoms does not mean you have HIV. Other illnesses can cause the same symptoms.

Some people may not feel sick during early HIV infection. During this earliest stage of HIV infection, the virus multiplies rapidly. After the initial stage of infection, HIV continues to multiply but at lower levels. 

When people with HIV do not receive treatment, more severe HIV symptoms may appear years later, as HIV develops into AIDS. People with AIDS have weakened immune systems that make them prone to opportunistic infections. 

Opportunistic infections are infections and infection-related cancers that occur more frequently or are more severe in people with weakened immune systems than in people with healthy immune systems. See the What is an Opportunistic Infection? fact sheet to learn more.

Without treatment, HIV transmission is possible at any stage of HIV infection—even if a person with HIV has no symptoms.

How is AIDS diagnosed?

Symptoms such as fever, weakness, and weight loss may be a sign that a person’s HIV has advanced to AIDS. However, an AIDS diagnosis is based on the following criteria:

• A drop in CD4 count to less than 200 cells/mm³
  OR
• The presence of certain opportunistic infections (known as AIDS-defining conditions)

Although an AIDS diagnosis indicates severe damage to the immune system, HIV medicines can still help people at this stage of HIV infection.

This fact sheet is based on information from the following sources:

From the Centers for Disease Control and Prevention:

• About HIV
• How HIV Spreads

From the HIV Clinical Practice Guidelines at Clinicalinfo.HIV.gov:

• Guidelines for the Use of Antiretroviral Agents in Pediatric HIV Infection:
  • Introduction
• Recommendations for the Use of Antiretroviral Drugs During Pregnancy and Interventions to Reduce Perinatal HIV Transmission in the United States
  • Preventing HIV Transmission During Infant Feeding

From MedlinePlus:

• HIV
• HIV Medicines

From the National Institute of Allergy and Infectious Diseases (NIAID):

• HIV/AIDS

Also see the HIV Source collection of HIV links and resources.

What is HIV testing?

Testing for HIV determines if a person has acquired HIV. HIV is the virus that causes AIDS, which is the third and most advanced stage of HIV infection.

HIV testing can detect if you have HIV, but it cannot tell how long you have had HIV or what stage of HIV infection you are in. See the HIVinfo The Stages of HIV Infection fact sheet to learn more about how HIV progresses when untreated.

Why is HIV testing important?

There are two reasons why HIV testing is important:

• First, an estimated 15 percent of people with HIV in the United States are unaware they have HIV, and the Centers for Disease Control and Prevention (CDC) estimates that about 40 percent of new HIV diagnoses are transmitted by those who are not aware of their HIV status. Knowing your HIV status can help keep you—and others—safe.
• Second, early identification and treatment of HIV is important to increase health and reduce related illnesses. Early and sustained treatment will help you live a long, healthy life.

If you have a negative HIV test:

A negative HIV test result shows that you do not have HIV. If you have certain risk factors, you need to continue taking steps, such as using condoms during sex, to avoid getting HIV. The chances of getting HIV may be higher for some people due to certain behaviors or situations. Examples of these individuals include:

• People who have unprotected sex with multiple partners or with strangers (such as sex workers)
• Health care workers who may come in contact with bodily fluids
• People who travel to areas where HIV is common (such as sub-Saharan Africa)
• Men who have sex with men (MSM)
• People who inject drugs, specifically those who share needles

If you have certain risk factors for HIV, you can consider taking medicines to prevent HIV (called pre-exposure prophylaxis, or PrEP). For more information, read the HIVinfo fact sheets on The Basics of HIV Prevention and Pre-Exposure Prophylaxis.

If you have a positive HIV test:

A positive HIV test result shows that you have HIV, but you can still take steps to protect your health and the health of your partners. Begin by talking to your health care provider about HIV medicines, known as antiretroviral therapy (ART). 

For more information about starting HIV treatment, see the HIVinfo HIV Treatment: The Basics and What to Start: Choosing an HIV Treatment Regimen fact sheets. 

Who should get tested for HIV?

The CDC recommends that everyone aged 13 to 64 years get tested for HIV at least once as part of routine health care. Generally, people who have more risk factors for HIV should get tested each year. Sexually active MSM may benefit from getting tested more often, such as every three to six months.

If you are older than 64 years, your health care provider may recommend HIV testing if you have certain risk factors that increase the chance of HIV transmission, such as:

• Having vaginal or anal sex with someone who has HIV or whose HIV status you do not know
• Injecting drugs and sharing needles, syringes, or other drug equipment with others
• Exchanging sex for money or drugs
• Having a sexually transmitted infection (STI), such as syphilis
• Having sex with anyone who has any of the HIV risk factors listed above

Talk to your health care provider about your risk for HIV and how often you should get tested for HIV.

Should pregnant women get tested for HIV?

CDC recommends that all pregnant women get tested for HIV so that they can begin taking HIV medicines as soon as possible if they have the virus. Pregnant women with HIV take HIV medicines during pregnancy and childbirth to reduce the chances of perinatal transmission of HIV and any personal health risks. 

For more information, read the HIVinfo Preventing Perinatal Transmission of HIV fact sheet.

What are the types of HIV tests?

There are three types of tests used to diagnose HIV: antibody tests, antigen/antibody tests, and nucleic acid tests (NATs). Your health care provider can determine the appropriate HIV test for you.

How soon each test can detect HIV infection differs, because each test has a different window period. The window period is the time between when a person may have been exposed to HIV and when a test can accurately detect HIV infection.

• Antibody tests check for HIV antibodies in blood or oral fluid. Most rapid tests and at-home self-tests are antibody tests. Generally, antibody tests that use blood from a vein can detect HIV sooner than tests that use blood from a finger stick or oral fluid.
• Antigen/antibody tests can detect both HIV antibodies and HIV antigens in the blood and are the most common HIV tests. After HIV exposure, antigens will show up in the blood sooner than antibodies.
• NATs look for HIV in the blood taken from a vein. These tests may also be called viral load tests because they not only detect the virus but also determine the quantity of virus present in the blood. They can usually identify HIV as soon as 10 to 33 days after exposure. NATs are mostly used to monitor HIV treatment and not for routine screening because they are expensive.

A person’s initial HIV test will usually be either an antibody test or an antigen/antibody test. NATs are not routinely used for HIV screening unless the person has had a high-risk exposure or a possible exposure with early symptoms of HIV infection.

When an HIV test is positive, a follow-up test will be conducted for confirmation to rule out inaccurate test results, known as a false positive result. Sometimes people will need to visit a health care provider to take a follow-up test using another blood sample.

Other times, the follow-up test may be performed in a lab using the original blood sample to ensure that the first positive result was accurate.

Is HIV testing confidential?

HIV testing can be confidential or anonymous. 

Confidential testing means that your HIV test results are not available to the public. Instead, your test results are included in your medical record and generally reported to local or state health departments to be counted in statistical reports.

Any personal or identifiable information, such as your name or address, is removed before creating statistical reports or sharing with other health organizations, including the CDC.

Anonymous testing means you do not have to give your name when you take an HIV test. When you take the test, you receive a number. To get your HIV test results, you use the number instead of your name.

Where can someone get tested for HIV?

Your health care provider can give you an HIV test. If you feel apprehensive about talking to your personal physician or family doctor, HIV testing is also available at many hospitals, medical clinics, substance use programs, and community health centers. Use CDC's GetTested treatment locator to find an HIV testing location near you.

Getting tested through a professional health care provider is recommended; however, HIV self-testing kits are available. There are two types of HIV self-tests—rapid self-tests and mail-in self-tests—but state laws may limit their availability in some locations

A rapid self-test is an oral fluid (not the same as saliva) test done entirely at home or in private. The U.S. Food and Drug Administration (FDA) has approved one rapid HIV self-test called the OraQuick In-Home HIV test. More information about the OraQuick In-Home HIV Test is available on the FDA website.

This fact sheet is based on information from the following sources:

From CDC:

• Getting Tested for HIV
• Self-Testing
• Vital Signs: Ending the HIV Epidemic

From FDA:

• Information Regarding the OraQuick In-Home HIV Test

From Medicare:

• HIV Screenings

From MedlinePlus:

• HIV Screening Test

From the National Library of Medicine:

• HIV Testing

Also see the HIV Source collection of HIV links and resources.

What is the HIV life cycle?

Viruses cannot multiply by themselves. They must enter and take over the target cells to make copies of the virus. The multiple steps involved in virus multiplication occur inside the infected cells and are collectively termed the “virus life cycle.”

HIV can recognize and infect the CD4 cells (CD4 T lymphocytes) of the immune system, destroying many of these cells in the process. CD4 cells are a type of white blood cell that help protect the body from infection with viruses, bacteria, and fungi. HIV uses components of the CD4 cells to multiply in large numbers and spread throughout the body.

What are the seven stages of the HIV life cycle?

The HIV virus is very small at about 100 nanometers in diameter (about one-thousandth of the thickness of a regular sheet of paper). Despite its small size, the virus is composed of multiple components that are essential to its progression through the HIV life cycle, such as the capsid and envelope.

Figure 1. Structure of an HIV Particle

The various components of the HIV particle each play an important role in the HIV life cycle, allowing the particle to infect CD4 cells and make more copies of the virus. The seven stages of the HIV life cycle are:

1. Binding: HIV binds to receptors on the surface of a CD4 cell.
2. Fusion: The HIV envelope fuses with the CD4 cell membrane, allowing HIV to enter the CD4 cell.
3. Reverse transcription: Inside the CD4 cell, HIV releases and uses reverse transcriptase (an HIV enzyme) to convert its genetic material (HIV RNA) into HIV DNA. This allows HIV to enter the CD4 cell nucleus.
4. Integration: Inside the CD4 cell nucleus, HIV integrase (an HIV enzyme) helps HIV integrate its viral DNA into the DNA of the CD4 cell.
5. Replication: Once integrated into the DNA of the CD4, HIV uses parts of the CD4 cell to create long chains of HIV proteins, allowing HIV to build more and more particles.
6. Assembly: New HIV proteins (from the replication stage) and HIV RNA move to the surface of the cell and assemble into immature (non-infectious) HIV.
7. Budding: Newly formed immature HIV pushes itself out of the host CD4 cell. New HIV then releases protease (an HIV enzyme) to break apart protein chains in the immature virus, creating a mature (infectious) virus.

Figure 2. Stages of the HIV Life Cycle

It is reported that during the acute stage of HIV infection, about 10,000 new HIV particles can be produced from one CD4 cell, resulting in an increase in the number of infected CD4 cells.

What is the connection between the HIV life cycle and HIV medicines?

Research scientists design drugs that target specific stages of the HIV life cycle to obstruct or block the virus from multiplying to prevent damage to CD4 cells. As a result, the number of CD4 cells remains high and the person with HIV maintains normal immune function.

Antiretroviral therapy (ART) typically includes a combination of HIV medicines from different drug classes (at least two) to treat HIV infection. People on ART take a combination of HIV medicines (called an HIV treatment regimen) every day (pills) or every one or two months (injections). HIV medicines from different drug classes protect the immune system by blocking HIV at different stages of the HIV life cycle.

Because an HIV treatment regimen includes HIV medicines from at least two different HIV drug classes, ART is very effective at blocking the virus and preventing HIV from multiplying in large numbers.

Having less HIV in the body protects the immune system and prevents HIV from advancing to AIDS. While ART cannot cure HIV, it can help people with HIV live long, healthy lives. HIV medicines also reduce the risk of HIV transmission, preventing the spread of HIV to others.

This fact sheet is based on information from the following sources:

From the National Institute of Allergy and Infectious Diseases:

• HIV Replication Cycle
• Antiretroviral Drug Discovery and Development

Also see the HIV Source collection of HIV links and resources.

HIV Infection

Without treatment, HIV infection gets progressively worse over time as the virus destroys key components of the immune system. Prolonged exposure to untreated HIV can eventually cause acquired immunodeficiency syndrome (AIDS).

There is no cure for HIV, but there is good news. Treatment with HIV medicines (called antiretroviral therapy or ART) can slow or prevent HIV from progressing into more serious forms. HIV medicines help people with HIV live long, healthy lives.

Research shows that people who start HIV treatment early can live as long as people who do not have the virus, largely due to the advancement of HIV medicines.

Stages of HIV Infection

The progression of HIV occurs in three stages over time (months and years) in people who don’t receive treatment. The stages of HIV infection include:

1. Acute HIV Infection

   Acute HIV infection is the earliest stage of HIV infection, and it generally develops within 2 to 4 weeks after infection with HIV. During this time, some people have flu-like symptoms, such as fever, headache, and rash. In the acute stage of infection, HIV multiplies rapidly and spreads throughout the body, attacking and destroying the infection-fighting CD4 cells (CD4 T lymphocytes) of the immune system. During this stage, the level of HIV in the blood is very high, which greatly increases the risk of HIV transmission.

2. Chronic HIV Infection

   The second stage of HIV infection is chronic HIV infection (also called asymptomatic HIV infection or clinical latency). During this stage, HIV continues to multiply in the body but at very low levels. People with chronic HIV infection may not have any HIV-related symptoms. Without ART, chronic HIV infection usually advances to AIDS in 10 years or longer, though in some people it may advance faster. People who are taking ART may be in this stage for several decades.

3. AIDS

   AIDS is the final, most severe stage of HIV infection, and causes severe damage to the immune system. As a result, the body cannot fight off opportunistic infections, also called AIDS-defining conditions. People with HIV are diagnosed with AIDS if they have a CD4 count of less than 200 cells/mm³ or if they have certain opportunistic infections. Once HIV progresses to the AIDS stage, a person can have a high viral load and transmit HIV to others very easily. Without treatment, people with AIDS typically survive about 3 years.

The image above depicts what happens in the blood of people with HIV throughout the stages of HIV infection. Without treatment, HIV slowly increases in number and attacks and destroys normal CD4 cells. A lack of CD4 cells severely limits the immune system’s ability to fight off other infections.

Can HIV be treated at different stages?

ART is very effective at reducing viral load to undetectable levels, particularly when started as early as possible during acute infection. Research trials found that there was a 53% reduction in the risk of death or serious illness if treatment was started with a high CD4 cell count.

People with chronic HIV infection may still transmit HIV to others; however, people who take ART exactly as prescribed and maintain an undetectable viral load during this stage have minimal risk of transmitting HIV to someone without HIV through sex.

Even if someone’s HIV progresses to AIDS, HIV medicines can still reduce the amount of HIV virus in the blood to undetectable levels, allowing more CD4 cells to regenerate. In turn, people taking these medicines will be less likely to acquire an opportunistic infection, despite an AIDS diagnosis.

Ultimately, virtually anyone with HIV can benefit from modern HIV medicines, regardless of what stage of HIV they are in.

How can I prevent HIV from progressing through the stages?

Once a person is diagnosed with HIV, they should start ART as soon as possible. One of the main goals of ART is to reduce a person's viral load to an undetectable level. People with HIV who maintain an undetectable viral load have effectively no risk of transmitting HIV to someone without HIV during sex and should maintain relatively normal immune function.

In addition, the Centers for Disease Control and Prevention suggests that having an undetectable viral load likely reduces the risk of HIV transmission through sharing of needles, syringes, or other drug injection equipment (such as cookers), but are unsure how much the risk is reduced.

Importantly, ART is only highly effective if taken exactly as prescribed. To ensure that HIV does not progress to more advanced stages, it is important to adhere to your prescribed medication schedule. In some cases, those who do not adhere to an ART schedule can develop resistance to their HIV medicines, making them ineffective.

Some people face challenges that make it hard to stick to a treatment plan and maintain an undetectable viral load. In this case, they should encourage their partners to take pre-exposure prophylaxis (PrEP). PrEP is medicine that people without HIV can take to prevent HIV infection, even if they get exposed to the virus.

This fact sheet is based on information from the following sources:

From HIV.gov:

• What Are HIV and AIDS?
• Symptoms of HIV

From the Centers for Disease Control and Prevention (CDC):

• About HIV

Also see the HIV Source collection of HIV links and resources.

What is a latent HIV reservoir?

A latent HIV reservoir is a group of immune system cells in the body that are infected with HIV but are not actively producing new virus particles.

HIV primarily attacks the immune system cells called CD4 cells (CD4 T lymphocytes). Although HIV almost always infects these cells, it does not always use them to replicate and create more HIV. When HIV uses CD4 cells to replicate, it produces a large amount of viral RNA, viral proteins, and virus particles.

As with most other viral infections, the body eventually recognizes infected cells that produce HIV as a threat, and the immune system destroys them.

However, some CD4 cells with HIV go into a resting, or latent, state. While in this resting state, the latent cells do not produce new virus particles or viral products. Therefore, the immune system does not recognize these cells as harmful and does not destroy them.

HIV can hide inside these cells for years, forming a latent HIV reservoir. These cells can be stored throughout the body, including within the central nervous system, lymphatic system, and genital tract.

Importantly, cells in the latent reservoir can become active again at any time and start making more virus particles. To find out more about how HIV attacks cells, read the HIVinfo HIV Life Cycle fact sheet.

Do HIV medicines work against latent HIV reservoirs?

HIV medicines prevent HIV from multiplying by interfering with the HIV life cycle, which reduces the amount of the virus in the body (called the viral load). Because the HIV-infected cells in a latent reservoir are not producing new copies of the virus, HIV medicines have no effect on them.

People with HIV must take HIV medicines (called an HIV treatment regimen) to keep their viral loads low and stay healthy. If a person stops taking their HIV medicines, the infected cells of the latent reservoir can begin making HIV again, and the person's viral load will increase.

Although HIV medicines may not get rid of latent HIV reservoirs, it is important to continue taking HIV medicines as prescribed to prevent HIV from becoming active and replicating, even when viral load is low.

Are researchers studying ways to target latent HIV reservoirs?

Finding ways to target and destroy latent reservoirs has proven to be a major challenge for HIV researchers. Researchers are exploring different strategies for destroying HIV reservoirs or making them permanently dormant, including:

• Using gene therapy (manipulating genes to treat or prevent disease) to cut out certain HIV genes and inactivate the virus in immune cells infected with HIV.
• Developing drugs or other methods to reactivate latent HIV so that the HIV can be destroyed by the immune system or new HIV therapies.
  • The “shock and kill” or “kick and kill” strategy aims to reactivate latent HIV to make the virus visible to the immune system and susceptible to new HIV therapies. For example, broadly neutralizing antibodies (bNAbs) may help find and destroy CD4 cells hosting latent HIV. Additionally, immune checkpoint inhibitors may help eliminate reactivated HIV reservoirs.
  • The “block and lock” strategy permanently silences all HIV reservoirs, even after treatment interruption. A substantial part of the human DNA genome contains ancient retrovirus DNA (the same type as HIV) that is permanently dormant.

Although no method has been fully effective in removing latent HIV reservoirs, researchers are investigating new approaches like immunotherapy and combination strategies. Success in these areas could potentially lead to a cure for HIV.

What happens if you have a latent HIV reservoir?

Most people with HIV, including those who are taking HIV medicines, have an HIV reservoir. Unless new research (such as investigational drugs or vaccines) shows the ability to eliminate HIV particles from the body, it’s safe to assume you have a latent HIV reservoir if you have HIV, even if you have an undetectable viral load.

While some HIV may remain in the body, HIV medicines can effectively reduce the amount of virus in the body, allowing people with HIV to live long, healthy lives. People with HIV should focus on maintaining an undetectable viral load to stay as healthy as possible and reduce the chances of transmitting HIV to others.

This fact sheet is based on information from the following sources:

From the National Institute of Allergy and Infectious Diseases:

• HIV/AIDS Treatment
• HIV Viral Eradication
• Sustained ART-Free HIV Remission

Also see the HIV Source collection of HIV links and resources.

What is a preventive HIV vaccine?

All vaccines “teach” our immune system to recognize and effectively defend our bodies against viruses or bacteria. Examples of existing vaccines include those for polio, tetanus, and measles. Although preventive vaccines are available for many viruses, none are currently available for HIV.

When available, a preventive HIV vaccine will be given to people who do not have HIV, with the goal of preventing HIV infection if they are exposed to the virus. A preventive HIV vaccine teaches the immune system to protect against HIV in the event of an exposure to HIV.

Are there any FDA-approved preventive HIV vaccines?

No FDA-approved preventive HIV vaccines currently exist. However, scientists are pursuing innovative strategies to design an HIV vaccine to prevent or treat HIV infection.

Because no HIV vaccines have been approved by the FDA, experimental HIV vaccines are only available in clinical trials and are not available for purchase in the United States.

Research has shown promise regarding the potential for a preventive HIV vaccine. For example,  the RV144 trial showed the ability to reduce HIV infection by about 31 percent.

The RV144 trial helped to encourage additional research on HIV prevention, including the Antibody-Mediated Prevention (AMP) Studies, which found that broadly-neutralizing antibodies (bNAbs) could reduce HIV infection by up to 75 percent—but only for some strains of the virus.

Ongoing efforts aim to develop HIV prevention methods that are even more effective.

How is a preventive HIV vaccine different from a therapeutic HIV vaccine?

The goal of a preventive HIV vaccine is to prevent people from getting HIV before an exposure occurs. When available, it will be given to people who do not have HIV.

Unlike a preventive vaccine, a therapeutic HIV vaccine is for people who already have HIV. The goal of a therapeutic HIV vaccine is to strengthen the natural immune response to the virus for people with HIV.

To learn more about therapeutic HIV vaccines, read the HIVinfo What is a Therapeutic HIV Vaccine? fact sheet.

Can a person get HIV from a preventive HIV vaccine?

No, a person cannot get HIV from a preventive HIV vaccine. Unlike some vaccines (such as the flu vaccine), which use inactivated or weakened virus to build immunity, preventive HIV vaccines do not contain HIV.

Each preventive HIV vaccine being tested uses a slightly different design or strategy to build immunity to HIV, but none of them can actually transmit HIV. For example, past preventive HIV vaccines have targeted viral genes, proteins, and bNAbs to improve immunity against HIV.

Of the approximately 30,000 people who have participated in HIV vaccine studies around the world in the last 25 years, no one has gotten HIV from any of the vaccines tested.

Why is a preventive HIV vaccine important?

Treatment options for HIV have improved a lot over the last 40 years, offering effective ways to manage the virus and prevent transmission. However, using HIV medicines for treatment (known as antiretroviral therapy [ART]) or prevention (known as pre-exposure prophylaxis [PrEP]) can be challenging over a lifetime.

Like most other medicines, HIV medicines can be difficult to access in some areas and may have side effects and high costs. In addition, long-term ART requires strict adherence to a medicine schedule, which can be difficult for many people.

When people struggle to stick to a treatment schedule, they can develop drug resistance to certain HIV medicines and then must change to different medicines to keep HIV under control.

Researchers believe a preventive HIV vaccine will be the most effective way to control or eliminate new HIV infections by helping to overcome the limitations of HIV medicines.

What research is being done on preventive HIV vaccines?

Some of the areas of interest being studied in clinical trials include—

• Different ways of giving preventive vaccines, such as using a needle and syringe versus a needle-free device
• The immune responses that occur in people who receive a preventive vaccine
• The safety of preventive vaccines
• Whether a preventive vaccine protects against HIV infection
• If the vaccine contributes to viral suppression if a person in the study gets HIV

Where can a person get more information about clinical trials studying preventive HIV vaccines?

An online database of clinical trials on preventive HIV vaccines is available from the ClinicalTrials.gov study summaries. Click on the title of any trial in the list to see more information about the study.

If you are interested in participating in a vaccine study, you can also contact the National Institutes of Health Vaccine Research Center by calling 866-833-LIFE (5433) or by emailing [email protected].

To learn more about HIV clinical trials, read the HIVinfo HIV and AIDS Clinical Trials fact sheet.

This fact sheet is based on information from the following sources:

From the National Institutes of Health:

• History of HIV Vaccine Research
• HIV Vaccine Development
• Clinical trial of HIV vaccine begins in United States and South Africa (September 20, 2023)

From the International AIDS Vaccine Initiative (IAVI):

• IAVI Vaccine Literacy Library, IAVI, New York, USA, 2022

Also see the HIV Source collection of HIV links and resources.

What is a therapeutic HIV vaccine?

A therapeutic HIV vaccine is a vaccine that is designed to improve the body’s immune response to HIV in people who already have the virus.

In 2012, a therapeutic HIV vaccine called Vacc-4x showed that it may be possible to teach the immune system to control HIV in some people with HIV and reduce their viral load.

Researchers are developing and testing therapeutic HIV vaccines to achieve HIV remission or a functional cure. The goal of a therapeutic vaccine is to keep HIV at undetectable levels (known as undetectable viral load) without the need for regular antiretroviral therapy (ART).

Currently, ART is the only recommended treatment for HIV infection and involves using a combination of different HIV medicines to prevent HIV from multiplying. A person with HIV must remain on ART to keep HIV at undetectable levels.

In summary, researchers are exploring the use of therapeutic HIV vaccines to—

• Slow down the progression of HIV in people with the virus
• Achieve HIV remission, also called a functional cure (keeping viral load suppressed without the need for ART)

As an added benefit, a therapeutic HIV vaccine may also make it less likely that a person with HIV could transmit it to others.

Are there any FDA-approved therapeutic HIV vaccines?

Currently, no therapeutic HIV vaccines are approved by the FDA. However, scientists are pursuing innovative strategies to design an HIV vaccine to prevent or treat HIV infection.

To develop an effective therapeutic HIV vaccine, scientists continue creating vaccines that target different parts of the virus (such as the Env gene or Gag proteins) or components of the immune system (such as broadly neutralizing antibodies, or bNAbs). These strategies aim to improve the body’s ability to control HIV.

While previous research has shown only limited success, ongoing advancements in vaccine technology, immune-based therapies, and gene-editing approaches provide hope that a therapeutic HIV vaccine will eventually be developed. For now, you must be enrolled in a clinical trial to receive an experimental HIV vaccine.

Why is a therapeutic vaccine important?

Treatment options for HIV have continuously improved over the years by improving the number of options and ease of use, while also minimizing side effects. However, adhering to an HIV treatment regimen over a lifetime can be difficult for many people.

Many HIV medicines must be taken every day to be effective. Although some long-acting HIV medicines can be taken less often, these medicines are not appropriate for everyone with HIV and still require a strict medicine schedule to work as intended (see the HIVinfo Long-Acting HIV Medicine fact sheet for more information).

Access to HIV medicines can be difficult in some situations, and some medicines may have side effects or high costs that deter people from taking them as prescribed. Over time, missed doses can lead to drug resistance, and a treatment regimen may need to be changed.

A therapeutic HIV vaccine could help to effectively control HIV while overcoming the limitations of HIV medicines. At a minimum, a therapeutic HIV vaccine could reduce the amount of HIV in the body, reduce how often HIV medicines must be taken, and help prevent drug resistance.

How is a therapeutic HIV vaccine different from a preventive HIV vaccine?

The goal of a preventive HIV vaccine is to prevent people from getting HIV. When available, it will be given to people who do not have HIV. To learn more, read the HIVinfo What is a Preventive HIV Vaccine? fact sheet.

A therapeutic HIV vaccine is for people who already have HIV. The goal of a therapeutic HIV vaccine is to strengthen the natural immune response to the HIV that is already in people with the virus.

Where can a person get more information about clinical trials studying therapeutic HIV vaccines?

An online database of clinical trials on therapeutic HIV vaccines is available from the ClinicalTrials.gov study summaries. Click on the title of any trial in the list to see more information about the study.

If you are interested in participating in a vaccine study, you can also contact the National Institutes of Health Vaccine Research Center by calling 866-833-LIFE (5433) or by emailing [email protected].

To learn more, read the HIVinfo fact sheet on HIV and AIDS Clinical Trials.

This fact sheet is based on information from the following sources:

From the National Institute of Allergy and Infectious Diseases:

• HIV Vaccine Development
• Sustained ART-Free HIV Remission
• Clinical trial of HIV vaccine begins in United States and South Africa (September 20, 2023)

From the International AIDS Vaccine Initiative (IAVI):

• IAVI Vaccine Literacy Library

Also see the HIV Source collection of HIV links and resources.

What is an investigational HIV drug?

As defined by the U.S. Food and Drug Administration (FDA), an investigational HIV drug is an experimental drug that is being studied to determine:

• Whether the drug is safe and effective
• If and how the drug may be used in a specific population (such as adults, children, pregnant women)
• How much of the drug is needed
• Potential benefits and risks of taking the drug

Investigational HIV drugs are studied in a series of medical research studies called clinical trials to determine if they are safe, if they work, and how they should be used. Clinical trials progress through three phases before drug sponsors submit a New Drug Application to the FDA for formal review.

If the FDA determines that the drug meets regulatory standards, the drug may be approved for general use or sale in the United States. In some cases, a drug may require a Phase 4 trial to ensure it is safe long-term.

Overall, the FDA looks at data from clinical trials to make sure that new drugs are not too risky, work for the people they’re meant to help, and can be made safely and reliably.

What types of investigational HIV drugs are being studied?

HIV treatment has come a long way since the first antiretroviral drug (zidovudine) was approved in 1987. Today, there are over 40 FDA-approved drugs used to treat HIV. Most people with HIV can live a normal lifespan by taking a combination of two or more HIV drugs.

Although modern HIV treatment regimens are generally safe and effective, they still have some limits, and researchers are looking for ways to make them even better. The table below outlines examples of common limitations and solutions under investigation.

How are clinical trials of investigational drugs conducted?

Clinical trials are conducted in phases. Each phase has a different purpose and helps researchers answer different questions about the investigational drug.

• Phase 1 trial: Initial testing in a small group of people (20-80) to make sure the drug does not pose unacceptable risks. At this point, researchers also look for signs that the new drug or treatment is effective.
• Phase 2 trial: Testing in a larger group of people (100-300) to confirm the drug works as intended and to further evaluate its safety.
• Phase 3 trial: Continued testing in large groups of people (1,000-3,000) to confirm the drug’s effectiveness, monitor side effects, compare it with standard or equivalent treatments (to see if it is better than current medicines), and collect information to ensure that the investigational drug can be used safely.

In most cases, an investigational drug must be proven effective and must show continued safety in a Phase 3 clinical trial to be considered for approval by the FDA for sale in the United States.

In rare cases, drugs go through the FDA’s Accelerated Approval Program and are approved before a Phase 3 clinical trial is complete. Accelerated approval requires early data suggesting benefit for serious conditions (such as some cancers) that lack effective treatments. Additional studies are still required to prove the drug is safe and effective. If the drug is not proven to be safe and effective, it may be withdrawn.

• Phase 4 trial: Ongoing tracking that occurs after a drug is approved by the FDA for sale in the United States. The purpose of the tracking is to seek more information about the drug’s risks, benefits, and optimal use. Phase 4 trials are not always required.

For more information, read the HIVinfo HIV and AIDS Clinical Trials fact sheet.

How can a person find a clinical trial that is studying an investigational HIV drug?

There are several ways to find an HIV and AIDS clinical trial that is searching for volunteer participants:

• To find an HIV and AIDS clinical trial that is studying an investigational HIV drug, use the “Find Studies” search feature on ClinicalTrials.gov.
• For help with your search, call a Clinicalinfo health information specialist at 1-800-448-0440 or email [email protected].
• Join ResearchMatch, which is a free, secure online tool that makes it easier for the public to become involved in clinical trials.

Not everyone will be able to participate in clinical trials using investigational HIV drugs. Many studies have strict criteria on who can participate in the study, including factors like age, sex, health, other conditions or infections, and sexual orientation.

Some people may not be able to join a clinical trial because the study requires commitment to many appointments or is only available in a specific area.

Are investigational HIV drugs available for use outside of a clinical trial?

In some cases, an investigational HIV drug may be available through an expanded access program (sometimes called “compassionate use program”). Expanded access programs allow for the use of an investigational drug outside of a clinical trial to treat a person who has a serious or immediately life-threatening disease and who has no FDA-approved treatment options.

Drug companies must have permission from the FDA to make an investigational drug available for expanded access. People seeking expanded access to an investigational HIV drug should talk to their health care provider to see if they qualify to participate in an expanded access program.

Is it safe to use an investigational HIV drug?

One goal of HIV research is to identify safer HIV medicines that are equally or more effective than existing HIV medicines. Researchers try to make clinical trials as safe as possible. However, taking an investigational HIV drug can involve both benefits and risks.

The most notable risks of taking investigational drugs include unexpected side effects from the drug, which may be unpleasant, serious, or even life-threatening.

The exact benefits and possible risks of participating in a clinical trial or an expanded access program are explained before someone starts using an investigational drug through a process called informed consent.

How can a person find more information on investigational HIV drugs?

To find more information on an investigational HIV drug, use the Clinicalinfo Drug Database, which includes up-to-date information on many investigational HIV drugs.

This fact sheet is based on information from the following sources:

From the National Institutes of Health (NIH):

• NIH Clinical Research Trials and You: The Basics
• NIH Clinical Research Trials and You: Finding a Clinical Trial

From the National Institute of Allergy and Infectious Diseases (NIAID):

• HIV/AIDS

From the U.S. Food and Drug Administration (FDA):

• Understanding Investigational Drugs
• Expanded Access | Information for Patients

Also see the HIV Source collection of HIV links and resources.

How can HIV be transmitted?

The human immunodeficiency virus (HIV) is a virus that spreads through certain body fluids. Once someone has HIV, the virus remains in the body and can be transmitted to others through these fluids:

• Blood
• Semen (including preseminal fluid)
• Vaginal fluids
• Rectal fluids
• Breastmilk

If a person has enough of the virus in their body, either because they are not taking HIV medicine (known as antiretroviral therapy, or ART) or their medicine is not working effectively, they can pass the virus to others through any of the fluids above.

How does HIV spread?

HIV is most commonly spread through unprotected vaginal or anal sex. According to the Centers for Disease Control and Prevention (CDC), sexual contact accounts for at least 89 percent of all new HIV diagnoses.

However, HIV can still be transmitted through other means, including—

• Shared needles or drug injection equipment: HIV can spread when people share needles (for drug injection, tattoos, or piercings) or other drug injection equipment that are contaminated with contagious blood.
• Perinatal HIV transmission: Babies can be exposed to HIV while breastfeeding or through contaminated blood during pregnancy and childbirth, especially if ART is not taken during or after pregnancy.
• Medical settings: HIV can be transmitted through blood transfusions or accidental needle sticks, but these are uncommon in the United States due to strict safety measures.
• Other blood exposures: In extremely rare cases, HIV can be spread by sharing personal items like a razor or toothbrush, by eating pre-chewed food from someone with HIV, or by accidental exposure to blood from an open wound of someone with HIV. These situations would require a large amount of blood (more than usual) and a direct way for it to enter the body (such as an open sore or cut).

While it is possible to transmit HIV through all of the means above, the likelihood of transmission depends on several different factors.

How likely is HIV transmission?

The chances of transmitting HIV vary based on a number of factors. Most importantly, HIV can only be transmitted through sex if someone has a detectable viral load. There is virtually no risk of transmitting HIV through sex if someone with HIV is treated and has an undetectable viral load. 

Simply, if someone is taking their HIV medicines and the medicines are working as they are intended, they cannot spread HIV to others through sex. This is known as Undetectable = Untransmittable or U=U. Learn more about how HIV treatment works in HIV Treatment: The Basics.

The U=U concept applies specifically to HIV transmission through sex. However, having an undetectable viral load greatly lowers the chance of passing HIV through other routes, like during childbirth or by sharing needles.

If someone is not treated for HIV or the HIV medicines are not working as intended, then transmission is more likely. As noted above, HIV is most commonly spread through condomless sex, but the chances of transmission vary based on the type of sex. According to the CDC, the estimated risk of HIV transmission per 10,000 exposures is—

• 138 (1.38%) for receptive anal sex
• 11 (0.11%) for insertive anal sex
• 8 (0.08%) for receptive penile-vaginal sex
• 4 (0.04%) for insertive penile-vaginal sex
• Rare but not impossible for receptive or insertive oral sex

Importantly, the numbers above only apply when exposure happens with someone who has a detectable viral load.

In the United States, the chances of HIV transmission through means other than sexual activities are the highest through perinatal transmission or via shared needles. For instance, the estimated risk of HIV transmission through shared needles during injection drug use is 63 in 10,000 exposures, nearly eight times the odds of transmission through vaginal sex.

Aside from the means above, the chances of transmitting HIV are relatively low in the United States. For instance, the per-exposure risk of HIV transmission is the highest through blood transfusions with contaminated blood, but strict screening protocols minimize that risk to less than one in a million in the United States.

In what ways can HIV not be transmitted?

There are many misconceptions about how HIV can be transmitted. HIV cannot be transmitted through—

• Casual contact:
  • Hugging
  • Kissing (closed mouth)
  • Shaking hands
• Environmental surfaces or items:
  • Air
  • Door handles
  • Shared food, drinks, or utensils
  • Swimming pools
  • Toilet seats
• Body fluids:
  • Mucus (including when coughing or sneezing)
  • Saliva
  • Sweat
  • Tears
  • Urine
• Insects or animals:
  • Ticks, mosquitoes, or other insects
  • Dogs, cats, or other household animals

There may be extremely rare exceptions to the above list if large amounts of blood are present. For example, HIV is not spread through saliva, but if contaminated blood is mixed with saliva due to an injury, bleeding gums, or open sores, transmission could be possible (although unlikely).

What increases the likelihood of HIV transmission?

When someone is untreated or has an HIV treatment regimen that is not working effectively, some behaviors can further increase the chances they will spread HIV to others. Such behaviors include—

• Having sex without a condom
• Having multiple sex partners
• Having untreated sexually transmitted infections (STIs), such as genital herpes
• Having unprotected sex with a partner who has untreated STIs
• Having a high viral load
• Using drugs that impact judgment or decision-making
• Sharing needles or drug injection equipment

What prevents HIV transmission?

Taking HIV medicines as scheduled is the most effective way to prevent spreading HIV to others. In addition, regular viral load testing can help to make sure a treatment regimen continues to be effective over time.

For those who are not treated, struggle to take HIV medicines as prescribed, or are taking a treatment regimen that isn’t working effectively, HIV transmission can be prevented by—

• Practicing safer sex practices like using a condom correctly every time you have sex
• Having a partner take pre-exposure prophylaxis before a possible exposure
• Having a partner take post-exposure prophylaxis after a possible exposure
• Disclosing your HIV status to others, particularly sexual partners

Otherwise, for people who are sexually active and may not know their HIV status, regular testing is an important way to help prevent the spread of HIV. Since HIV often has no symptoms, it can unknowingly be transmitted to others.

This fact sheet is based on information from the following sources:

From CDC:

• How HIV Spreads
• HIV Diagnoses, Deaths, and Prevalence
• Living with HIV
• Undetectable = Untransmittable

From World Health Organization:

• HIV/AIDS