Too soon to view HIV vaccine as a solution

by Cesar Chelala

NEW YORK — The results of a new HIV vaccine trial in Thailand, although encouraging since they show a lowered rate of infection among those vaccinated, should be treated with cautious optimism.

The hope of a breakthrough is, nonetheless, excellent news, considering that every day 7,000 people worldwide are newly infected with HIV and that in 2007 over 2 million people died of AIDS according to UNAIDS (Joint United Nations Program on HIV/AIDS).

The trial of the new AIDS vaccine was carried out in parts of Thailand. The vaccine was given to 16,402 volunteers between 18 and 30 years old and deemed to be at average risk of HIV infection. The vaccine used was a combination of two vaccines that, when tried in isolation, had not affected infection rates. It was based on HIV strains that circulate commonly in Thailand.

The trial was carried out by the U.S. Army, the Thai Ministry of Public Health, the U.S. National Institute of Allergy and Infectious Diseases, and the patent-holders of the two key components of the vaccine, Sanofi- Pasteur and Global Solutions for Infectious Diseases.

Half of the volunteers received the vaccine, and the other half received a placebo. Participants in the study were tested for HIV infection every six months for three years. Both groups received counseling on how to prevent HIV infection, first at the beginning of the study and then every six months.

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 groups behind the study claim these results indicate a 31 percent 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, according to Dr. Jerome H. Kim of the U.S. 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 the data obtained are indeed important, it is still necessary to be cautious about the implications. For example, RV144, the vaccine tested in Thailand, was designed to combat the strain of HIV that is most common in Southeast Asia. Different strains circulate in the U.S., Africa and other countries, and there is no indication that the vaccine could function effectively 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 although it can be claimed that the difference between the vaccinated group and the placebo group is statistically significant, it is too small to suggest the vaccine could be considered for use in the immediate future.

What is important, though, is that this study shows a positive response on an issue that has offered little hope so far. If the positive results can be repeated or improved under different conditions, we can expect to conquer an infection of tremendous medical, human and economic cost to society.

Cesar Chelala, M.D., Ph.D., is an international public health consultant for several U.N. agencies.