Updated January 2013
A vaccine is a treatment that prevents us from getting a disease. It works by teaching our immune system how to protect itself against a disease-causing germ like a virus or bacteria.
Vaccines are one of the world’s most effective tools for preventing diseases. Serious illnesses like polio, smallpox, measles, and mumps have been nearly eliminated from many countries because of vaccines.
There are two types of vaccines being studied for HIV: preventive vaccines and therapeutic vaccines. Preventive vaccines are designed to keep people from being infected with HIV. Therapeutic vaccines would allow those already infected with HIV to control the virus without needing to take HIV drugs.
In a best-case situation, a preventive HIV vaccine would protect nearly everyone who receives it from being infected with HIV. But many scientists think that the first-generation HIV vaccines will provide more limited forms of protection, in which some, but not all of the people who receive the vaccine are protected against becoming infected.
It is good to remember that none of the vaccines that are currently available (e.g., those for measles, polio, chicken pox) are 100 percent protective in 100 percent of the people who receive them. Some vaccines work better in some people than in others; other vaccines only provide protection for a limited amount of time. Yet these vaccines have been very effective and are now considered ‘tried and true.’ Therefore, even a partially protective HIV vaccine could be a very important tool for slowing the spread of HIV. It would also help scientists develop more effective vaccines over time.
Right now, most of the potential vaccines that are being developed are designed to prevent HIV infection in HIV-negative people. However, there are also research studies testing vaccines in people living with HIV (HIV+). While these therapeutic vaccines will not cure HIV, they may help HIV+ people fight the virus. They would allow HIV+ people to control the virus while taking fewer or no HIV drugs.
No. Each vaccine being tested uses a slightly different design or strategy but none of them can actually cause HIV infection. This is because all the potential vaccines only use small, synthetic (human-made) pieces of HIV. It is important to know that, while HIV vaccines cannot cause infection, people who have been vaccinated against HIV and who do not have HIV infection may have antibodies for HIV in their bloodstream. Therefore, in order for people who have been vaccinated against HIV to have their HIV status properly tested, they must use viral tests rather than antibody tests. For more information, see our “What tests are available?” section in our What Is HIV? info sheet.
No. Today there are no effective HIV vaccines.
Yes. There are more than 35 clinical trials of vaccines going on in over 20 countries around the world.
Like all experimental medical treatments, potential HIV vaccines go through a series of safety tests—first in animals and then in small groups of people. These small studies help determine whether or not the vaccine causes any serious side effects. Only vaccines that appear to be completely safe are considered for studies in larger groups of people that test whether the vaccine works. HIV vaccines are not tested by exposing people to HIV on purpose.
Before a research study on the effectiveness of a preventive vaccine begins, scientists usually spend two or more years looking at communities where studies may take place. They gather many types of information, including how many people get HIV each year. The rate of new infections is called the incidence rate. If 100 HIV-negative people were followed for one year, and five of them got HIV by the end of the year, you would say that there was a five percent incidence rate in that group of people.
Once these numbers have been collected, people from the community are asked to enroll in the preventive vaccine study. People in the study are randomly assigned to receive either the vaccine or a placebo (an inactive substance). Neither the researchers nor the study participants know who has received the vaccine and who has received the placebo.
The people in the study are followed for a long time—usually two to three years. At the end of the study, the researchers look to see whether the incidence rate is lower in the group of people who were given the vaccine, as compared to the group of people who were given the placebo.
For example, if there was a two percent incidence rate in people who received the vaccine, and a five percent incidence rate in people who received the placebo, that might mean that the vaccine was protecting some people against HIV.
The search for an HIV vaccine has not been easy. A number of potential vaccines have been studied since the mid-1980s, but few have made it to Phase III trials. Phase III trials test a product’s effectiveness and safety in very large groups of people over several years. It is only after a vaccine successfully passes a Phase III trial that the US Food and Drug Administration (FDA) can approve it for public use. For more information about all phases of clinical trials, see our Understanding Clinical Trials info sheet.
There have been three large Phase III trials of preventive HIV vaccines. The first two involved a potential vaccine called AIDSVAX. They were completed in 2003 and did not show any evidence that the vaccine worked.
The third trial took place in Thailand and enrolled 16,000 people, making it the largest HIV vaccine study ever. It tested AIDSVAX with another vaccine called ALVAC. In 2009, after much debate over the results, researchers concluded that the vaccine only had a modest effect in preventing HIV infection.
There had been high hopes for a fourth trial called STEP, which was a smaller study of a vaccine manufactured by Merck. In 2007, the STEP study and another study of the same vaccine in South Africa were called off early due to results that showed the vaccine did not work.
In 2012, a therapeutic vaccine called Vacc-4x showed that it may be possible to teach the immune system to control HIV reproduction in some HIV+ people and reduce their viral load. This would reduce their need for HIV drugs and decrease their exposure to side effects from the drugs. Future testing of Vacc-4x includes: (1) combining it with Vacc-C5, which is designed to stimulate the production of antibodies that reduce HIV-associated immune hyperactivation (which leads to AIDS), and (2) re-vaccinating those who received Vacc-4x to see if a second vaccination can further reduce viral load.
Yes. Despite setbacks, the search for an HIV vaccine has not ended. The disappointing STEP study results and the controversy over the results of the Thai study caused a lot of debate among researchers and advocates about what to do next. However, research is still moving forward. The focus is on answering basic scientific questions that can help guide vaccine development, while continuing to learn valuable information from previous studies and mapping out future ones.
A number of potential vaccines remain in development and evidence from different studies suggests that an effective HIV vaccine is still possible.
The next potential vaccine was developed by the National Institutes of Health (NIH) Vaccine Research Center (VRC). An effectiveness study called PAVE 100 was scheduled to begin for this vaccine in 2007, but was put on hold when the STEP results were announced.
The trial has since been redesigned and renamed HVTN 505. It is a study looking at the safety and effectiveness of the VRC’s vaccine. HVTN 505 has enrolled 2,200 HIV-negative men who have sex with men; results are expected in 2013.
The honest answer is that we do not know. It takes several years to study whether a potential vaccine is safe and effective. Based on what is now in development and research studies, scientists believe it will be six to ten years before the first HIV vaccine is licensed for use. This first-generation vaccine is not likely to provide complete protection against HIV infection.
Although this sounds discouraging, it is important to remember that vaccine research takes a long time. It has taken decades, with more setbacks than advances, to discover other vaccines. Because effective vaccines have ended many epidemics in modern times, it is important to keep moving ahead with HIV vaccine research.
Yes. Vaccine trials provide a lot of information to people who are thinking about volunteering to be in the study and to people who decide to join the study. One of the key messages is that there is no way of knowing whether the vaccine is effective before the study ends. That makes it important for everyone who joins to continue protecting themselves by enjoying safer sex and using clean needles.
This message is repeated to participants every time they come for a study visit. By educating people in the study, it is possible that the research study reduces the participants’ risk for getting HIV. All studies also provide free male condoms and counsel participants about other methods like the female condom or safe injection practices.
Over 30 years into the epidemic, we still do not have ways to protect ourselves against HIV infection during sex that are private, woman-controlled, and independent of our partners’ agreement. There is an urgent need for prevention methods that women can choose without their partners’ knowledge or consent. An effective HIV vaccine would give women this option. A woman could decide to be vaccinated against HIV. Later on she might decide to talk about the decision with her partner—or she might not. The choice would be hers.
Women need to participate in large numbers in HIV vaccine studies in order to find an HIV vaccine that helps protect us. This is the only way that researchers will be able to find out whether a particular vaccine works equally well in women and men. In Africa, where women bear a larger burden of the HIV epidemic than men, only about one in five HIV vaccine trial participants is a woman. As a result, scientists are concerned that study results will point us toward vaccines that may only be effective in men.
An effective HIV vaccine could also someday be given to infants born to HIV+ women to help protect the infants from getting HIV through breast milk. This would be very useful in developing countries where feeding with formula is not possible for many HIV+ women.
Until there is an effective HIV vaccine, the best way to protect yourself and your loved ones from HIV is by practicing safer sex and not sharing needles.