Yesterday, at a scientific meeting in Seattle, researchers announced that Merck’s AIDS vaccine is susceptible to increase the risk to becoming H.I.V.-infected. In September, Merck stopped the vaccine trial because it failed to prevent infection and also to lower the amount of H.I.V. in the infected participants, the two main objectives of the research.

Merck’s vaccine was being tested among 3,000 volunteers at high risk of developing AIDS in nine countries, including the United States. The risk increased wider in the vaccinated group than in placebo group. Also male participants were at higher risk than females.

This trial was considered one of the most promising experimental AIDS vaccines. Scientists consider that this trial should be analyzed and reviewed in order to verify failure hypothesis.

The AIDS Vaccine Advocacy Coalition said that this study new data brought “more question than answers for the field of AIDS vaccine,” and therefore AIDS scientists should not begin testing other vaccines until definitive drawn conclusions from Merck’s vaccine thorough analysis.

Merck’s vaccine used the latest technology, namely a modified virus, called adenovirus type 5, as a vector to deliver three synthetic H.I.V. genes. The researchers said that this vaccine itself cannot cause AIDS, but in this trial, it might have activated the immune system to be more susceptible to H.I.V. infection when exposed to AIDS virus. This may lead to a hypothesis that maybe other ingredients than adenoviruses are necessary in constructing an AIDS vaccine. For that further research is needed.