September 25, 2009
New York, N.Y. -- Yesterday it was reported that an HIV vaccine regimen led to a marginal but statistically significant degree of protection against acquisition of HIV infection. The only information provided by the trial sponsors in their press releases is that 74 out of 8,198 volunteers who received placebo immunizations became infected with HIV compared to 51 out of 8,197 volunteers who received a combination of two vaccines, ALVAC vCP1521 and AIDSVAX B/E. Seven of the original 16,402 volunteers were excluded from the efficacy analyses after it was found that they were HIV-infected at the time of receiving their first vaccination. The result equates to a protective efficacy of a little over 31%, but with a very wide "95% confidence interval" spanning from 1.1% to 52.1% (a confidence interval is a statistical method for conveying the degree of uncertainty associated with a result; if the lower bound of the confidence interval is less than 1, the result is not statistically significant). The vaccines had no effect on post-infection viral load levels among the recipients who became infected.
These results are very welcome given the many unwelcome surprises that have assailed the HIV vaccine field over the past few years. However, based on the limited amount of information that has been released, it appears that the statistical significance hangs on very few cases of HIV infection. TAG urges caution in interpreting the findings until more detailed information is available. In light of the potential importance of the results to efforts to prevent HIV infection, and the level of public interest, TAG is disappointed that the trial sponsors did not include more data with their news releases.
When the trial was launched, TAG stated our concern that the lack of data on the efficacy of ALVAC alone would preclude an understanding of whether the inclusion of AIDSVAX added to, or subtracted from, any potential benefit (Science 305;5681:180). Now that there is an indication of possible efficacy, this issue looms large. Many people worked diligently and in good faith on this trial and it is disheartening that such a huge undertaking is still unable to provide definitive answers as to the efficacy of the candidates studied. Instead, if the results hold up to scrutiny, more trials will be required to try and understand what happened.
TAG will provide additional information and commentary on the trial results when the details become available.