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 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 studies are safe and effective in people. Results from a Phase 1 Trial, Phase 2 Trial, and Phase 3 Trial are used to determine whether a new drug should be approved by the U.S. Food and Drug Administration for sale in the United States. Once a new drug is approved, researchers continue to track its safety in a Phase 4 Trial.

Interventional trial and observational trial are two main types of clinical trials:

• An interventional study tests (or tries out) an intervention—a potential drug or treatment, medical device, or procedure—in people. Interventional studies are often prospective and are specifically tailored to evaluate the direct effects of new drugs or treatments on disease.
• An observational study does not test potential treatments. Instead, researchers observe participants on their current treatment plan and track health outcomes. Observational studies (also called epidemiologic studies) are mostly retrospective.

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 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. Other studies include people who do not have HIV.

Participation in an HIV and AIDS clinical trial may also depend on other factors, such as age, sex, pregnancy, HIV treatment history, or other medical conditions.

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

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.

Sometimes people get paid for participating in a clinical trial. For example, they may receive money or a gift card. They may 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 treatment for HIV 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.

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 person decides to participate in an HIV and AIDS clinical trial, will their personal information be shared?

The privacy of study volunteers is very important to everyone involved in an HIV and AIDS clinical trial. The informed consent process includes an explanation of how a study volunteer’s personal information is protected.

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 a case study search feature ClinicalTrials.gov to find HIV and AIDS studies looking for volunteer participants.
• 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.

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

From the National Library of Medicine:

• Learn About Clinical Studies

From the Food and Drug Administration:

• Clinical Trials: What Patients Need to Know
• Informed Consent for Clinical Trials

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 abbreviation “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, causing health decline and the onset of 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, and the immune system can recover. A healthy immune system protects against other infections.

See the The Stages of HIV Infection fact sheet for a more complete overview of how HIV progresses to AIDS.

How is HIV transmitted?

HIV can be transmitted through bodily fluids, including blood, semen (“cum”), pre-seminal fluid (“pre-cum”), 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 HIV-positive blood through accidental needle sticks
• Sharing personal items that may have blood (such as razors or toothbrushes)
• Being exposed through placental exchange during pregnancy
• Eating pre-chewed foods (in case of open sores or bleeding gums)

Semen, Pre-Seminal Fluid, Vaginal Fluids, and Rectal Fluids:

• Having vaginal or anal sex
• Having oral sex (less likely, but can occur in rare cases)
• Being exposed to vaginal fluids during childbirth

Breast Milk:

• Breastfeeding

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 fact sheet on Preventing Perinatal Transmission of HIV.

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 infection. People on ART take a combination of HIV medicines (called an HIV treatment regimen) every day (pills) or by 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 on injectable HIV medicines.

ART is recommended for everyone who has HIV. ART prevents HIV 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 HIV medicines 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.

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 one percent when someone breastfeeds with an undetectable viral load.  

Feeding infants using properly prepared formula or pasteurized human donor milk from a milk bank can completely eliminate the chances of perinatal HIV transmission. 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 can reduce the risk of getting HIV, particularly with partners who have HIV with a detectable viral load or whose HIV status is unknown. 

Other behaviors, like avoiding sharing needles and choosing safer sex practices (such as limiting the number of sexual partners), can also reduce the likelihood of HIV transmission.

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 every two months for injections—before an HIV exposure. For more information, read the HIVinfo fact sheet on Pre-Exposure Prophylaxis (PrEP).

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

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
• AIDS and Opportunistic Infections

From the NIH Office of AIDS Research:

• 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 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 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 are HIV negative:

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 are HIV positive:

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).

People on ART usually take a combination of oral HIV medicines (as a single pill or multiple pills) every day to treat HIV infection. In some cases, doctors prescribe long-acting injections instead of pills to treat people with HIV. These injections are given by health care providers once a month or every other month and require routine office visits.

ART is recommended for everyone who has HIV, and people with HIV should start ART as soon as possible. ART cannot cure HIV, but HIV medicines help people with HIV live long, healthy lives.

A main goal of ART is to 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 effectively no risk of transmitting HIV to a partner without HIV through sex (known as Undetectable = Untransmittable, or U=U). 

Who should get tested for HIV?

The Centers for Disease Control and Prevention (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 test positive. 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 fact sheet on Preventing Perinatal Transmission of HIV.

What are the types of HIV tests?

There are three types of tests used to diagnose HIV infection: 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 done with blood from a finger stick or with oral fluid.
• Antigen/antibody tests can detect both HIV antibodies and HIV antigens in the blood and are the most commonly used 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 wasn’t a false positive. Talk to your health care provider who will determine your HIV risk factors and the best type of HIV test for you.

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 give 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. Rapid self-test and mail-in self-test are the two types of HIV self-tests, but state laws regarding self-testing 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.

Like most other viral infections, these infected cells that produce the virus are eventually recognized as a threat to the body and destroyed by the immune system.

However, some HIV-infected CD4 cells go into a resting or latent state. While in this resting state, the infected but latent cells do not produce new virus particles or viral products. Therefore, these cells are not recognized as harmful infected cells by the immune system and are not destroyed.

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 HIV Life Cycle fact sheet from HIVinfo.

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 to 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 is a major challenge facing 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 HIV-infected immune cells.
• 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 yet, researchers are investigating new approaches like immunotherapy and combination strategies to eliminate latent HIV reservoirs. Success in these areas could potentially lead to a cure for HIV in time.

What happens if you have a latent HIV reservoir?

Most people with HIV, including those who are taking HIV medicines, will 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 your viral load is undetectable.

While some HIV may remain in the body, HIV medicines can effectively reduce the amount of virus in the body, and allow 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 while reducing 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 are polio, tetanus, and measles. 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 will teach our immune system to protect against HIV in case we are ever exposed to the virus.

Are there any FDA-approved preventive HIV vaccines?

After almost four decades of research, there are currently no U.S. Food and Drug Administration (FDA)-approved preventive HIV vaccines. However, scientists are pursuing innovative strategies to design an HIV vaccine to prevent or to treat HIV infection. You must be enrolled in a clinical trial to receive an experimental HIV vaccine (see more details below).

Are there any FDA-approved preventive HIV vaccines?

After almost four decades of research, there are currently no U.S. Food and Drug Administration (FDA)-approved preventive HIV vaccines. However, scientists are pursuing innovative strategies to design an HIV vaccine to prevent or to treat HIV infection. You must be enrolled in a clinical trial to receive an experimental HIV vaccine (see more details below).

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. When available, it will be given to people who do not have HIV.

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 that is already in people with HIV.

Researchers are exploring the use of therapeutic HIV vaccines to:

• Slow the progression of HIV infection in people with HIV.
• Achieve HIV remission, also called a functional cure (keeping viral load suppressed without the need for antiretroviral therapy [ART]).

To learn more, 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. The preventive HIV vaccines being studied in clinical trials do not contain HIV. Each vaccine being tested uses a slightly different design or strategy but none of them can actually transmit 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 30 years. However, like most other medicines, HIV medicines can have side effects, can be expensive, and can be hard to access in some countries. Also, some people may develop drug resistance to certain HIV medicines and then must change to different medicines.

Using condoms correctly every time and taking pre-exposure prophylaxis (PrEP) can help prevent HIV transmission.

Researchers believe a preventive HIV vaccine will be the most effective way to control or completely eliminate new HIV infections.

What research is being done on preventive HIV vaccines?

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

• The safety of preventive vaccines.
• Whether a preventive vaccine protects against HIV infection.
• Whether a preventive vaccine controls HIV if a person gets HIV while enrolled in a study. Participants can get HIV through sexual contact or from sharing drug injection equipment while they are participating in a clinical trial. As stated above, a person cannot get HIV from the HIV vaccine being tested.
• The immune responses that occur in people who receive a preventive vaccine.
• Different ways of giving preventive vaccines, such as using a needle and syringe versus a needle-free device.

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, 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 Institutes of Health:

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

From the HIV Vaccine Trials Network (HVTN):

• How Vaccines Work
• HIV Vaccine Myths and Facts
• HVTN Trials

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 a person who already has HIV.

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 is that treating people with these vaccines would keep HIV at undetectable levels (known as undetectable viral load) without the need for regular antiretroviral therapy (ART). ART is the recommended treatment for HIV infection and involves using a combination of different HIV medicines to prevent HIV from multiplying. Currently, 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 progress of HIV infection in people with HIV.
• 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 HIV to others.

Are there any FDA-approved therapeutic HIV vaccines?

After almost four decades of research, there are currently no U.S. Food and Drug Administration (FDA)-approved therapeutic HIV vaccines. However, scientists are pursuing innovative strategies to design an HIV vaccine to prevent or treat HIV infection. You must be enrolled in a clinical trial to receive an experimental HIV vaccine (see more details below).

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 HIV.

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 HIV Vaccine Trials Network:

• How Vaccines Work
• HIV Vaccine Myths and Facts
• HVTN Trials

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 it is safe and effective.
• How the drug may be used in a specific situation (adults, children, pregnant women, etc.).
• How much of the drug is needed.
• Information about the potential benefits and risks of taking the drug.

Investigational HIV drugs are studied in a series of medical research studies called clinical trials. Once an investigational HIV drug has been proven safe and effective in a clinical trial, drug sponsors formally propose the FDA approve it as a new medicine for sale and marketing in the U.S. by submitting a New Drug Application. After reviewing the clinical trials, the FDA may approve the drug for general use or sale in the United States.

What types of investigational HIV drugs are being studied?

Since the first antiretroviral drug was described, HIV treatment has come a long way. Today, there are over 40 FDA-approved drugs to treat HIV. Most people with HIV can live a normal life span by taking a combination of two or more HIV drugs. However, some people find it hard to remember to take their prescribed HIV medicine every day, especially if they have substance use or mental health disorders. Others develop drug-resistant strains of HIV, which means that the virus mutates so that the medications they take are no longer effective. Many times, these two factors go together: forgetting to take HIV medicines allows HIV to multiply, which increases the risk of drug resistance and, therefore, HIV treatment failure.

To fill these gaps in treatment, researchers are investigating:

• New and better HIV drugs for the treatment of heavily treatment-experienced adults with multi-drug resistant HIV infections.
• Improvement and wider availability of long-acting antiretroviral therapy, the latest innovation in HIV treatment medication (usually requiring two injections every 1 or 2 months, instead of pills every day).
• Development of new formulations of long-acting antiretroviral therapy with an autoinjector device that makes it easy and safe for patients to inject the drug themselves at home, most likely under the skin. Researchers hope that this method will increase privacy and medication adherence.
• Development of new versions of long-acting antiretroviral drugs as an “ultra-long-acting treatment and prevention” that could be injected every four months, and ultimately every six months by the end of the decade.

HIV researchers are also studying investigational vaccines to prevent HIV and treat HIV. The goal of a preventive HIV vaccine is to prevent HIV in people who do not have HIV but who may be exposed to the virus. A safe and effective HIV treatment vaccine (also called a therapeutic HIV vaccine) could prevent HIV from advancing to acquired immunodeficiency syndrome (AIDS), replace the daily use of HIV medicines, and help prevent HIV transmission. 

To learn more, read the HIVinfo What is a Preventive HIV Vaccine? and What is a Therapeutic HIV Vaccine? fact sheets.

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 evaluate the drug’s safety and to identify side effects. 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 determine the drug’s effectiveness 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. (However, some drugs go through the FDA’s accelerated approval process and are approved before a Phase 3 clinical trial is complete.)

• 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.

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 a study 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].
• You can also join ResearchMatch, which is a free, secure online tool that makes it easier for the public to become involved in clinical trials. 

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”). Expanded access allows for the use of an investigational drug outside of a clinical trial to treat a person who has a serious or immediate 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 may qualify to take part in an expanded access program.

Is it safe to use an investigational HIV drug?

One goal of HIV research is to identify safer, more effective HIV medicines. Researchers try to make clinical trials as safe as possible. However, taking an investigational HIV drug can involve both benefits and risks. Risks may include unexpected side effects from the drug, which can be unpleasant, serious, or even life-threatening.

The benefits and possible risks of participating in a clinical trial or an expanded access program are explained to people before they decide whether to participate through a process called “informed consent.” The informed consent process involves disclosing to potential research participants all the information needed to make an informed decision about whether to participate in the clinical trial.

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:

• 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.