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HIV Vaccines

December 20, 2015

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How Are HIV Vaccines Tested?

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.

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 fewer people got HIV who were in the group of people given the vaccine, as compared to in the group of people given the placebo.

For example, if two out of 100 people who received the vaccine got HIV, and five out of 100 people who received the placebo got HIV, that might mean that the vaccine was protecting some people against HIV.

What Results Have Been Seen in HIV Vaccine Research?

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 can governmental agencies like the US Food and Drug Administration (FDA), European Medicines Agency (EMA), or Medicines and Healthcare products Regulatory Agency (MHRA in the UK) approve the vaccine for public use. For more information about all phases of clinical trials, see The Well Project's Understanding Clinical Trials.

Preventive Vaccine Research

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.

Another potential vaccine was developed by the National Institutes of Health (NIH) Vaccine Research Center (VRC). In 2013, a trial named HVTN 505, which tested the VRC's vaccine among over 2500 HIV-negative men, was stopped because the vaccine neither prevented HIV infection nor reduced viral load in those who became infected with HIV.

Therapeutic Vaccine Research

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 people living with HIV and reduce their viral load. Further testing has showed that Vacc-4x can help reduce the viral load in people living with HIV, but not enough to for them to stop taking their HIV drugs. A Phase I trial (first time in humans) of a therapeutic vaccine called Vacc-5C showed that Vacc-5C was safe and well tolerated, generated an immune response, and may improve some people's response to vaccination with Vacc-4x.

Is HIV Vaccine Research Going Forward?

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. In fact, scientists continue to discover new potential ways to stop HIV, including the finding of a vaccine that triggers the body to produce broadly neutralizing antibodies to HIV. Because HIV mutates, or changes, so quickly, it is important to trigger an immune response against several strains of HIV.

Broadly neutralizing antibodies are antibodies that are effective at neutralizing several strains of HIV. Because HIV mutates, or changes, so quickly, it is important for a potential vaccine to trigger an immune response against several strains of HIV. Scientists have discovered ways to make some of these broadly neutralizing antibodies in the lab. These pre-made antibodies can then be given to people directly in a process known as 'passive immunization' (active immunization refers to the natural process in which your body's immune system makes antibodies itself). Recent research in monkeys has shown that broadly neutralizing antibodies have the potential to protect against infection and to reduce the amount of HIV in the body of those already living with HIV.

How Long Will it Take to Find an HIV Vaccine That Works?

The honest answer is that we do not know. It takes several years to study whether a potential vaccine is safe and effective. 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.

Do Vaccine Trials Do Anything to Help Lower the Participant's Risk of Becoming Infected With HIV?

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.

Taking Care of Yourself

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 drug injection equipment.

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This article was provided by The Well Project. Visit The Well Project's Web site to learn more about their resources and initiatives for women living with HIV. The Well Project shares its content with to ensure all people have access to the highest quality treatment information available. The Well Project receives no advertising revenue from or the advertisers on this site. No advertiser on this site has any editorial input into The Well Project's content.

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