An announcement, by researchers from the US Army and Thailand, at a recent press conference of the first positive results from an HIV vaccine trial was met with media fanfare but cautious optimism from scientists.

The RV 144 vaccine, which combines two vaccines (ALVAC and AIDSVAX) that alone were unsuccessful in previous clinical trials, showed moderate success at preventing HIV infection. Seventy-four of the 8,198 people who received the placebo became infected with HIV, compared with 51 of the 8,197 vaccinated individuals: a statistically significant 31% protection efficacy ( Nature News , 24 Sep 2009).

This finding “is certainly an encouraging advance for the HIV vaccine field”, said Dr Anthony Fauci, Director of the US National Institute of Allergy and Infectious Diseases, which is one of the trial's backers ( BBC News , 24 Sep 2009).

However, reports published online by Science (5 Oct 2009) and in The Wall Street Journal (12 Oct 2009) have questioned the findings. A second analysis of the trial data, which excludes participants in both groups that did not strictly adhere to the trial design and was not disclosed at the press conference, has been revealed by anonymous researchers who were given confidential briefings on the data; it suggests that the vaccine might be only 26% effective, which is not statistically significant.

According to Dr. Fauci, including both results “would have confused everybody” and the first analysis is “the gold standard” ( The New York Times , 11 Oct 2009).

The full results are due to be presented at the AIDS Vaccine 2009 conference in Paris on 20 October, and according to Colonel Jerome Kim, a researcher with the US Army who helped run the study, “everyone should wait until the data are out.” ( Science , 5 Oct 2009.)