VaxGen releases results of Thai Phase III trial

On 12 November the VaxGen company announced the results of the second Phase III trial of its vaccine candidate AIDSVAX, which was designed to protect HIV-negative people from HIV infection and disease. The company said that the vaccine offered no protection in a study of 2546 intravenous drug users (IDUs) in Thailand. A Phase III trial of a very similar version of AIDSVAX took place in 5417 homosexual men and high risk women from North America and Europe. Results from this trial were released earlier this year and also showed that the vaccine gave no overall protection.

Although the scientific results were negative there were positive lessons from the Thai trial. The vaccine was safe and did not cause any serious side effects. Importantly, volunteers did not report increased rates of high-risk behavior. One concern for AIDS vaccine trials is that volunteers might assume that they have received an effective vaccine and so increase high-risk behavior—even though during the trial they receive ongoing counseling that there is no way of knowing whether they have been given an effective vaccine and that they should not assume that they are protected from HIV infection. The Thai trial also showed that IDUs can be reliable participants in lengthy vaccine trials; more than 90 percent of the original participants completed the 3-year trial.

The November announcement of the Thai trial data did not mention VaxGen’s earlier claims of race- and gender-based effects. In February when the company announced the data from its first Phase III trial it claimed that there were signs of different levels of protection in non-white populations (AfricanAmericans, Hispanics, Asians and others) as compared to whites, and in women as compared to men. Since then, additional data analysis has not produced any evidence to support these claims.