Researchers Defend HIV Vaccine Study As Full Results Show More Modest Benefit In Some Groups

Main Category: HIV / AIDS
Also Included In: Immune System / Vaccines;  Clinical Trials / Drug Trials
Article Date: 22 Oct 2009 - 5:00 PDT

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Full results published on Tuesday in the New England Journal of Medicine from an HIV vaccine trial in Thailand hold up to scrutiny, researchers involved in the trial say, Reuters reports (Fox, Reuters, 10/20). According to results reported last month, the experimental vaccine prevented about 31% of new HIV cases among 16,000 participants in Thailand over three years -- a result that was considered "modest but statistically significant," according to the Wall Street Journal (Naik, Wall Street Journal, 10/21). The vaccine used in the trial is a combination of Sanofi-Pasteur's ALVAC canary pox/HIV vaccine and AIDSVAX, now owned by Global Solutions for Infectious Diseases (AP/New York Times, 10/20).

The research team used three different statistical analyses but had provided results from only one in their initial report, prompting criticism that they oversold their findings (McNeil, New York Times, 10/21). The two additional analyses published on Tuesday indicate that the vaccine is beneficial but might not provide definitive protection against HIV, according to the AP/New York Times (AP/New York Times, 10/20). At issue was the type of statistical method used to analyze the data, Reuters reports (Reuters, 10/20). According to the newly released analyses, the vaccine was 26% effective, with a 16% probability that the results were due to chance. Clinical trials typically have a limit of a 5% probability that the results are due to chance, according to the New York Times (New York Times, 10/21).

In one analysis, 12,452 participants who received all six doses on schedule, 86 contracted HIV. Thirty-six of those new infections occurred in the vaccine group and 50 occurred in the placebo group. Although not statistically significant, researchers said that the vaccine appeared more effective among low- to moderate-risk groups, compared with high-risk groups such as injection-drug users or people who visit commercial sex workers (AP/New York Times, 10/20).

Although the full results show the vaccine's protection "is turning out to be even more modest than originally advertised," many HIV/AIDS researchers "say the findings are still important," according to the Washington Post (Brown, Washington Post, 10/21). "The bottom line is that those results are real," Alan Bernstein, executive director of the Global HIV Vaccine Enterprise, said (AP/New York Times, 10/20). In an accompanying NEJM commentary, Raphael Dolin of Beth Israel Deaconess Medical Center and Harvard Medical School said that study was meticulously designed and conducted. "Although the merits of each type of analysis can be debated, all three yielded a possible, albeit modest, effect of the vaccine in preventing HIV infection," he said.

Jerome Kim, a U.S. Army colonel at the Walter Reed Army Institute of Research and one of the trial's leaders, defended his study's results and methodology, noting that the research passed a peer review by independent reviewers at NEJM. He cautioned that the study's findings are modest and difficult to interpret. The vaccine is far from ready for use by the general public and might not be effective for use in African countries, which have some of the highest HIV/AIDS prevalence rates worldwide. The team still needs to study how long the protection lasts and how much each of the two vaccines used in the study contributed to protection against HIV (Reuters, 10/20).

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