The results of a new HIV vaccine trial in Thailand, although positive since it shows a lowered the rate of infection amongst those vaccinated, should be treated with cautious optimism. It is, nonetheless, excellent news particularly considering that every day 7,000 people worldwide are newly infected with HIV and that in 2007 over two million people died of AIDS according to UNAIDS (The Joint United Nations Programme on HIV/AIDS).

The new AIDS vaccine was tried in 16,000 volunteers aged between 18 and 30 in parts of Thailand and was carried out by the US Army, the Thai Ministry of Public Health, the US National Institute of Allergy and Infectious Diseases and the patent-holders of the two components of the vaccine, Sanofi-Pasteur and Global Solutions for Infectious Diseases.

The vaccine used in this trial was a combination of two vaccines that when tried singly had not cut infection rates. The vaccine combination was based on HIV strains that circulate normally in Thailand. Participants in the study were tested for HIV infection every six months for three years.

The study was carried out in 16,402 volunteers at average risk of HIV infection. Half of the volunteers received the vaccine combination and the other half received a placebo. Both groups received counseling on how to prevent becoming infected with HIV at the beginning of the study and every six months after the start of the study for a total of three and a half years.

Among the participants in the study, new infections occurred in 51 of the 8,197 people given the vaccine, and in 74 of the 8,198 among those who received the placebo. The results indicate that there was a 31% lower risk of infection among those who had received the vaccine.

Although the number of infections in each group under study is relatively small it is statistically significant, as indicated by Dr. Jerome H. Kim, who is the army’s HIV vaccine program. Dr. Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases, concurred on the importance of the results.

Although those obtained are indeed important results it is still necessary to be cautious about its implications. For example, the RV144, the vaccine tested in Thailand, was designed to combat the most common strain of the HIV circulating in Southeast Asia. Different strains circulate in the U.S., Africa and other countries and there is no indication yet that the vaccine could function in similar ways when confronted with different HIV strains.

In addition, the number of people involved in the study shows the need for larger, more expensive trials. And finally, although the difference among subjects who had received the vaccine and those who hadn’t is statistically significant, it is still relatively small to consider it for use in the immediate future.

hat is really important, however, is that this study shows a positive response on an issue that up until now had not offered any hopes for solution. If the positive results are shown to be constant and even increase under different conditions we can expect to conquer an infection of tremendous medical, human and economic costs to society.

Cesar Chelala, MD, PhD, is an international public health consultant for several UN agencies.