In a story certain to be covered with a certain amount of hyperbole (to be fair, often due to the editors and not the science reporters), the results of an unusual HIV study conducted in Thailand are appearing in the news this week.
HIV breakthrough as scientists discover new vaccine to prevent infection
Miracle Vaccines Cut HIV Risk
Before one gets too excited about the story, check out the invaluable ScienceInsider from the AAAS blog, for a more balanced account:
Massive AIDS Vaccine Study a "Modest" Success
A large clinical trial of an AIDS vaccine has, for the first time, yielded positive results. But researchers immediately questioned the relevance of the data, which indicated that the vaccine offered only modest protection against infection by HIV.
The controversial trial, conducted with more than 16,000 volunteers in Thailand over the past 6 years, tested the effectiveness of two AIDS vaccines used together as a one-two punch. Researchers randomly assigned an equal number of participants who were at average risk of becoming infected by HIV to receive either the two vaccines or a saline placebo. At the end of the study in June, 51 of the vaccinated people had become infected within 3 years of receiving their last shot, compared with 74 people in the placebo group. The p value, which indicates whether results are due to chance, was less than 0.039, just below the widely accepted but arbitrary "significance" cutoff of 0.05. Surprisingly, the vaccine did not appear to suppress levels of the virus in the 51 people who became infected. No serious adverse events were seen in either group.
Here's another important caveat: scientists aren't certain why it was successful. It doesn't do what is expected: reduce the virus levels, or alter the host immune system response. More from Reuters:
HOW DOES THE VACCINE WORK?
Researchers are not sure. AIDS experts have long agreed that any HIV vaccine would have to activate both arms of the immune system -- the antibodies that home in on invaders such as viruses to neutralize them, and the T-cells that recognize and destroy viruses.
This vaccine did not appear to generate either response, and yet prevented infection 30 percent of the time.
Even more confusing, among the 51 people who were vaccinated but were infected anyway, the virus replicated just as well as it did among unvaccinated HIV patients. Researchers would not have expected that -- they would have expected the vaccine to at least make the infection less serious, as influenza vaccines do, for example.
"Additional studies are clearly needed to understand how this vaccine regimen reduced the risk of HIV infection," said Dr. Jerome Kim of the Walter Reed Army Institute of Research in Maryland, who helped lead the study.
There is an excellent review of the topic by Donald McNeil in the NY times today.
A vaccine is not just around the corner, and no expert will say it is. In the ’80s, top officials embarrassed themselves by predicting one in five years. At the time, the epidemic had killed a few hundred gay American men, hemophiliacs, drug users and transfusion recipients. No one imagined its death march would entrain 25 million as it circled the globe.
Take the results with a grain of sea salt. We all want to see progress in the worldwide battle against HIV/AIDS, but don't jump to too many conclusions about this story. There's much more work to be done to decipher the results. As WebMD notes,
Perhaps more importantly, the study fell far short of its goal of reducing the risk of HIV infection by 50%.
The numbers tell the story (McNeil again):
Still, for vaccinologists, last week’s news was momentous — after 20 years of constant failure, a vaccine appeared to have, for the first time, offered some protection. And it was the largest-ever clinical trial of its type.
But only the numbers that could be wedged into headlines were big. "One Third Protected" was a common one.
In the data itself, the real margin of success was razor-thin: 23 Thais out of 16,395.
That is, three years after getting the vaccine or a placebo, 74 in the placebo arm of the trial became infected while only 51 in the vaccine arm did.
On the other hand, the idea that an AIDS vaccine of any kind might be possible is certainly news worth following up on. But my advice is stick to the science journals and blogs on this one, and don't assume it's a 'miracle' just yet.