Plans for human trial of H.I.V. vaccine canceled

Plans for a large human trial of a vaccine against the AIDS virus in the United States were canceled on Thursday because federal health officials said the vaccine was unlikely to prove effective and might increase the risk of H.I.V. infection among volunteers.
The decision is another major setback in efforts to develop an H.I.V. vaccine, which health officials contend would be their best weapon to control the AIDS pandemic. Several other H.I.V. vaccines are in various stages of testing among people in many countries.

Scientists have been trying for more than 25 years to make an effective H.I.V. vaccine. They say that getting one to market — if one is ever developed — is years off.

After a meeting sponsored by the National Institute of Allergy and Infectious Diseases in March, many AIDS experts said researchers needed to go back to the drawing board before they could develop an effective vaccine.

The trial canceled on Thursday was supposed to have begun enrolling 8,500 volunteers last October to receive a vaccine developed by the infectious diseases agency. The study is known as PAVE, for Partnership for AIDS Vaccine Evaluation. PAVE is a consortium of United States government agencies and government-financed organizations involved in developing and evaluating experimental H.I.V. vaccines. Its goal is to develop an effective vaccine that no pharmaceutical company or institution is likely to accomplish on its own.

But the PAVE trial was postponed after a test of a similar, much-heralded vaccine made by Merck failed in its two main objectives: to prevent infection and to lower the amount of H.I.V. in the blood among those who did become infected.

Also, the findings among the 3,000 participants in nine countries in which the Merck vaccine was tested suggested it might have increased the risk of becoming infected with H.I.V.

After a safety monitoring committee detected the problems with the Merck vaccine in September, the company stopped its study immediately.

Scientists have found no obvious explanation for the failure of the Merck vaccine, which had been considered the most promising candidate for an H.I.V. vaccine. The infectious diseases agency helped pay for the vaccine trials