Reports for NATAP

AIDS Vaccine 2001 Conference

September 6, 2001 Philadelphia, PA

Partially effective vaccine could slow HIV spread

PHILADELPHIA, Sep 10 (Reuters Health) - A preventive AIDS vaccine that is less than 100% effective could still help to control the epidemic, Dr. Ronald Gray of Johns Hopkins University and colleagues estimate.

Using data obtained from the Rakai Project studies in Uganda, Gray's group developed a model to look at how a protective or therapeutic vaccine would affect the spread of HIV. Gray reported the results here Saturday at the first international scientific meeting on AIDS vaccines--AIDS Vaccine 2001.

In the calculations, Gray used the basic reproductive number (Ro<1.0), which he defined as how low you must reduce transmission to ensure that an infected individual does not transmit the virus. At a Ro of less than 1.0, the epidemic would not be self-sustaining and the number of people infected with HIV would begin to drop.

The data used in the calculations included transmission probability per sex act, obtained from the Rakai cohort and published in The Lancet earlier this year.

Gray's team estimated that a vaccine with a 50% efficacy, combined with near complete coverage, would reduce transmission to Ro<1.0. A scenario of lower coverage (about 50%) could still achieve a Ro<1.0 with a vaccine with a 75% efficacy.

In addition, "we get more bang for our buck if we combine preventive vaccines with antiretroviral therapy," Gray told conference participants. "We can achieve lower incidence at much lower coverage.

"If we have a vaccine that reduces the viral load in the HIV-positive person, we would actually have the biggest impact," he continued. "If we had a vaccine that we could give to both negative and positive individuals, we would alleviate the need to do follow-up counseling."

Gray cautioned that "disinhibition" among participants in a vaccine program could be a big problem and "could totally offset any public health effects of a vaccine."

For example, it has been documented that since the advent of highly active antiretroviral therapy, the cocktail of potent drugs that has extended the lives of people with HIV, high-risk behaviors among men who have sex with men began to rise in the US after a prolonged period of steady decline.

The website for the Vaccine Conference is:
http://www.AIDSvaccine2001.org