Volunteers in AIDS vaccine trial may be at greater risk of infection

Nov 14 2007

Following the aborting of two international trials of an experimental AIDS vaccine, thousands of volunteers have been told the vaccine may have actually raised their risk of infection.

The trials which were conducted in the United States, Peru, Brazil, Dominican Republic, Haiti, Jamaica, Australia and South Africa, were halted in September after it became clear the vaccine did not prevent infection with the AIDS virus.

It was earlier this month that the researchers revealed there were some worrying indications that the vaccine somehow raised the risk of infection, although they insist the vaccine itself could not cause HIV infection.

Drug company Merck and the research team say they will now "unblind" the study so that all the participants can find out who received the active shot and who received a dummy injection.

The volunteers have already been informed and counselled that they could be at higher risk of HIV, a fatal and incurable virus that causes AIDS and have been encouraged to continue to return to their study sites regularly for ongoing risk reduction counseling and tests.

In order to test vaccines and new drugs, researchers always try to conduct what are called placebo-controlled, double-blinded trials which means in effect that neither the researchers nor the volunteers know who gets a placebo and who gets an active ingredient; this ensures there is no bias in determining the outcomes.

The vaccine researchers are now concerned about the future of their field as well as their volunteers.

The research team from Merck which makes the vaccine, and the National Institute of Allergy and Infectious Diseases believe a type of common cold virus used as the basis of the vaccine may somehow have made their volunteers more susceptible to HIV and still trying to work out how that has happened.

Out of 1,500 people vaccinated, 82 became infected with the AIDS virus, of these, 49 got the vaccine and 33 got a placebo shot; only one woman in the trial became infected with HIV.

The rest were men having sex with other men, and it seems it is the men who initially had the highest immune response to the adenovirus 5 common cold bug used to make the vaccine who were the most likely to become infected with the AIDS virus.

The infected men were also less likely to have been circumcised and may have engaged in more risky behaviour.

So whether the vaccine did actually do something remains a mystery and even vaccine advocates are calling it a setback.

AIDS has already killed 25 million people and affects 40 million more.