Frequently Asked Questions

Health and Safety Questions About Trial HIV Vaccines

Can I get HIV/AIDS from a study vaccine?

The HIV vaccines tested in people who are not infected do not use weakened or dead versions of HIV, which is how some other vaccines are made. Instead, HIV vaccines are made using genes or proteins that look like those found in the real virus, but are made in a lab. They do not have all of the working parts of the real HIV virus that are needed to cause infection. The vaccines used in these research studies cannot give people HIV.

Will the vaccines being tested cause me to give HIV to someone else?

No. This vaccine is not made from live virus or HIV-infected cells. You cannot become infected with HIV from the study vaccine or give the virus to someone else as a result of getting the vaccine.

If I am in an HIV vaccine study, am I protected from HIV infection?

You should never assume that you are protected from HIV infection because of your participation in a vaccine study. You should continue to practice safer sex and limit yourself to single-use, non-shared needles to reduce your risk of exposure to HIV. We do not know if a study vaccine will protect you from HIV, and you may have gotten a placebo, not the vaccine itself. (A placebo is a shot that looks just like the vaccine but does not have vaccine in it. Participants won’t know whether they got a placebo or the vaccine until the end of the trial.) If you think you might be at risk for HIV infection, seek counseling to learn about ways you can protect yourself. If you decide to join a vaccine study, the clinic staff will talk with you to help you think about ways of reducing your risks, and to be sure you know all of your options for HIV prevention.

What side effects can I expect from the vaccines being tested?

HIV vaccine study participants typically report few side effects. However, just like most licensed and approved vaccines, the HIV vaccines used in research studies may cause side effects such as soreness and redness at the injection site, low-grade fever, and body aches. These side effects usually do not last long, and tend to go away on their own.

Before you join the study, a member of the study staff will describe to you all of the risks and side effects that we know about, and any others that might be possible. This is part of the informed consent process—learning about a research study and deciding if you want to join. Study staff are available to talk about side effects and can also answer any other questions you have. There may also be side effects we do not know about. During the study, you will always be able to contact someone at the study clinic if you are unsure whether you are having a reaction to the vaccine.

If I receive a study vaccination, will I test positive on an HIV test?

If you join an HIV vaccine research study and get the study HIV vaccine, you may test positive on a standard HIV test, even if you are not infected with HIV. That’s because vaccines can cause the body to produce antibodies, and standard HIV tests measure the body’s antibody response to HIV; they do not directly measure HIV itself. There are no known medical side effects associated with having antibodies from a vaccine.

If you are participating in an HIV vaccine study, you should only be tested for HIV at the study site or a lab the site referred you to. There, clinicians can run more sensitive tests that can tell if you are have actually contracted HIV outside the study, or if your body is just making antibodies in response to the vaccine. To learn more about vaccine-induced antibodies, visit

Are there other kinds of risks to participating in a vaccine study?

Some volunteers have reported being treated poorly when others learned about the volunteers’ participation in a study. Some people believe that a study participant must be infected with HIV if they are in an HIV study, but that is false; volunteers must be HIV-negative to participate in preventive HIV vaccine studies. (We are trying to find a preventive vaccine to prevent HIV infection.)

On rare occasions, volunteers have had trouble getting health insurance and/or traveling outside of the United States. However, study staff and NIAID staff will assist you if you experience trial-related discrimination. It is important to remember that no one other than the study site staff will know you are taking part in an HIV vaccine study unless you tell them.

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Questions About Preventive HIV Vaccine Clinical Trials

What is the time commitment for participating in a vaccine study?

Each study is different, but a typical study lasts 1 to 2 years and requires 10 to 20 clinic visits. Each visit usually takes between 30 minutes and 3 hours. In general, the first few visits are longer because you are learning about the study, going through the informed consent process, and having a physical exam and blood tests to see if you are eligible to join the study. Details about the study visits and what is involved are part of the informed consent process.

How will you know if a vaccine works?

Studies that test whether an experimental vaccine works are called efficacy studies. Not all vaccine studies are efficacy studies. Early vaccine studies test if the study vaccine is safe to give to people, and whether people are able to take the study vaccine without becoming too uncomfortable. Another important goal of early studies is to test if people’s immune systems respond to the study vaccines. Efficacy studies are done after these smaller, early studies show the vaccine is safe and the immune system reacts to it.

When you go through the informed consent process, you will find out if the study you want to join is an early study or an efficacy study. Even if it is an efficacy study, it may take several years before the results are known. Efficacy studies can last as long as 5 years.

Regardless of what the study is looking for (whether it is safety or efficacy), all HIV vaccine studies teach us something important and bring us closer to finding a vaccine that works.

If I decide to participate, can I change my mind later?

Yes, you can leave the study at any time without any negative consequences. You are encouraged to take your time in deciding whether to join a vaccine study, so that you are comfortable and fully informed before you sign up. You may want to speak with your doctor, family, and friends before you decide to join.

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FAQ Source Information

Ending AIDS — Is an HIV Vaccine Necessary? Anthony S. Fauci, M.D., and Hilary D. Marston, M.D., M.P.H.
N Engl J Med 2014; 370:495-498February 6, 2014DOI: 10.1056/NEJMp1313771

Interview with Dr. Anthony Fauci on the need for an HIV vaccine and the advances that will help fulfill that need.
Supplement to the N Engl J Med 2014; 370:495-498

Meet the people making a difference in HIV prevention research.