Don't quit on an AIDS vaccine

Because hope is a treasure, a lot of people felt robbed by last week's surprising announcement that the trial of an experimental AIDS vaccine developed by Merck & Co. had been cut short. Many had hoped Merck's candidate would be the first to prove at least partly effective. That it didn't was disappointing. What would be worse is if we allow this news to slow progress toward developing a vaccine, which remains our best hope of reversing the epidemic. Now is precisely the time to do more.

The arithmetic hasn't changed. About 39 million people are HIV infected; 3 million die annually of AIDS. Life-prolonging treatments for AIDS have improved and have become more available and affordable even in poorer countries. But the epidemic outpaces these strides. For every person who began antiretroviral treatment last year, another six became HIV infected. What's more, these drugs are not cures, nor are they, because of resistance and toxicity problems, a lifelong solution for sufferers.

Skeptics now will argue even more loudly that it's impossible to create a vaccine against AIDS. I disagree. Research suggests that the human immune system is better at fighting HIV than we'd originally thought. Most people suppress the virus for many years before developing AIDS. A small number never contract the virus despite repeated exposure. Others are infected but haven't developed AIDS. If we can figure out the mechanism that makes this so, we'll have clues about how to engineer a vaccine -- how to equip the immune system for a fight against HIV before it gets exposed.

One encouraging sign: There are already vaccines against HIV's cousin, simian immunodeficiency virus, or SIV, that are highly effective in nonhuman primates. True, there are safety concerns that make a similarly designed HIV vaccine for people problematic. But if we could figure out why SIV vaccines work, we likely could reproduce their effect in people through safer means.

In science, failure is a teacher. The precise lessons of the Merck results will take time to decipher. But the called-off trial is far from the end of the line. Another 30 or so vaccine candidates are in various stages of testing. Perhaps more important, scientists already are devising alternative approaches, such as activating the antibody arm of the immune system rather than the T-cell arm, which was the basis of Merck's candidate and almost all the others.