by Bob Roehr
HIV vaccine research got a much-needed dose of encouraging news on Sept. 24 when results of a study conducted in Thailand were released. The study in more than 16,000 volunteers showed that those who received the vaccine were 31.2 percent less likely to become infected with HIV than those who received placebo shots (51 vs. 74 infections).
The $105 million study, which began enrolling participants in October 2003, combined two vaccines – ALVAC and AIDSVAX – that had shown no protection against infection in earlier individual trials. It consisted of four doses of the first vaccine and two doses of the second administered at fixed times over a six-month course. Participants were then monitored for three years.
Only the broad conclusion was released; more details will be presented at an HIV vaccine conference in Paris in late October.
“These new findings represent an important step forward in HIV vaccine research,” said Anthony S. Fauci, MD, director of the National Institute of Allergy and Infectious Diseases. It provided a large portion of the money for the study, which was conducted by the U.S. Army and Thai health officials.
While intriguing, the trial results may have raised more questions than they answered.
It is possible that the outcome was a statistical fluke. That is why science requires that findings be verified by one or more additional trials using similar methodologies.
Furthermore, researchers are puzzled as to why the vaccines that showed no protective effect when studied individually would create protection when they were combined.
Another major question is why the vaccine did not seem to affect the course of disease in those who become infected with HIV, which was the initial main goal of the Thai study. The viral load was about the same in both groups of participants who became infected.
A major research hypothesis has been that while it might not be possible to create a HIV vaccine that completely protects against becoming infected, it might be easier to create one that strengthens the immune system sufficiently to keep the infection from progressing to clinical disease. Ideally the body would be able to control the infection without using antiretroviral drugs.
Some of that immune-boosting effect was seen in the Merck vaccine trial that was stopped in the fall of 2007. The viral load of patients who became infected with HIV after receiving the vaccine was substantially lower than those who received placebo.
As Dr. Fauci said, “Additional research is needed to better understand how this vaccine regimen (in the Thai study) reduced the risk of HIV infection.”
Researchers will continue to study the trial participants, hoping to discover how the course of vaccination might have changed the participants’ immune response to better protect them against HIV infection.
This information then can be used to tweak the next generation of vaccines to produce even better immune protection.
The course of six vaccinations studied in this trial is so arduous and the protective effect is so low that no one envisions its widespread use as a tool of HIV prevention. There currently are no plans to seek FDA approval to sell the two products as a dual vaccine.