Plans for a large human trial of a promising government-developed HIV vaccine in the United States were canceled Thursday because a top federal official said scientists realized they did not know enough about how HIV vaccines and the immune system interact.
The decision is a major setback in an effort to develop an HIV vaccine that began 24 years ago when government health officials promised a marketed vaccine by 1987. Health officials have long contended that a vaccine would be their best weapon to control the AIDS pandemic.
A number of other HIV vaccines are in various stages of testing around the world. But there were high hopes for the government's trial because the potential vaccine was among a new class that seeks to stimulate the immune system in a different way.
The official who canceled the government trial, Dr. Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases, said it was becoming clearer that more fundamental research and animal testing would be needed before an HIV vaccine was ever marketed.
The government vaccine — known as PAVE, for Partnership for AIDS Vaccine Evaluation — was similar to a much-heralded vaccine that failed last year. That vaccine was developed by Merck, and Fauci's agency helped pay for the Merck trials.
Fauci said he reached his decision to cancel the coming trial after meeting with scientists to try to understand why the Merck vaccine had failed. He said he had concluded that scientists must go a step at a time because they did not yet know fundamental facts like which immune reactions are the most important in preventing the infection.
Dr. Alan Bernstein, executive director of the Global HIV Vaccine Enterprise, said that his organization supported Fauci's decision and that there was an "urgent need for a diversity of new approaches to HIV vaccine design."