【单选题】

Scientists said Thursday that a newAIDS vaccine, the first ever declared to protect a significant minority of humans against the disease, would be studied to answer two fundamental questions: why it worked in some people but not in others, and why those infected despite vaccination got no benefit at all.

The vaccine—known as RV 144, a combination of two genetically engineered vaccines, neither of which had worked before in humanslwas declared a qualified success after a six-year clinical trial on more than 16,000 volunteers in ThailanD、Those who were vaccinated became infected at a rate nearly one-third lower than the others, the sponsors said Thursday morning.
"I don’t want to use a word like ’breakthrough,’ but I don’t think there’s any doubt that this is a very important result," saidDr.Anthony S. Fauci, the director of the National Institute ofAllergy and InfectiousDiseases, which is one of the trial’s backers. "For more than 20 years now, vaccine trials have essentially been failures,"Dr. Fauci saiD、"Now it’s like we were groping down an unlit path, and a door has been openeD、We can start asking some very important questions."
It will still, however, take years of work before a vaccine that could end the epidemic, which has killed about 25 million people, can even be contemplateD、"We often talk about whether a vaccine is even possible," said Mitchell Warren, the executive director of theAIDS VaccineAdvocacyCoalition, orAVAC、"This is not the vaccine that ends the epidemic and says, ’O.K., let’s move on to something else.’But it’s a fabulous new step that takes us in a new direction."
In which direction is still unknown. No one—including the researchers from the United StatesArmy, the National Institutes of Health, the Thai Ministry of Public Health and two vaccine companies that tested the vaccine—knows why the vaccine gave even its weak indicator of success.
Experts generally disdain vaccines that do not protect at least 70 to 80 percent of those getting them.And this vaccine did not lower the viral loads of people who were vaccinated but caught the virus anyway, which was baffling because even mismatched vaccines usually do that. Simply repeating the trial to confirm the results would be pointless, experts agreeD、The trial, the largestAIDS vaccine trial in history, cost $105 million and followed 16,402 Thai volunteers. The men and women ages 18 to 30 were recruited from two provinces southeast of the capital,Bangkok, from the general population rather than from high-risk groups like drug injectors or sex workers. Half got six doses of two different vaccines; half were given placebos. For ethical reasons, all were offered condoms, taught how to avoid infection and promised lifelong antiretroviral treatment if they gotAIDS. They were then regularly tested for three years; 74 of those who got placebos became infected, but only 51 of those who got the vaccines diD、
Although the difference was a mere 23 people,Col. Jerome H. Kim, a physician and the manager of theAnny’s H.I.V. vaccine program, said it was statistically significant and meant that the vaccine was 31.2 percent effective. The results were surprising because both vaccines, one from the French company Sanofi-Aventis and one developed by Genentech but now licensed to Global Solutions for InfectiousDiseases, a nonprofit health group, had failed when used individually. "This came out of the blue," saidChris Viehbacher, Sanofi’s chief executive.Even 31 percent protection "was at least twice as good as our own internal experts were predicting," he addeD、In 2004, there was so much skepticism about the trial just after it began that 22 topAIDS researchers published an editorial in Science magazine suggesting that it was a waste of money.
One conclusion from the surprising result, saidAlanBernstein, head of the Global HIV VaccineEnterprise, an alliance of organizations pursuing a vaccine, "is