Plans for a large-scale trial of a potential AIDS vaccine are being dropped in favor of a smaller, more focused study, the National Institutes of Health said Thursday.

The trial of the vaccine, developed by the Vaccine Research Center at the National Institute of Allergy and Infectious Disease, had been planned to include 2,400 men in the United States in a study called PAVE 100.

However, the agency said that it decided that the vaccine did not warrant a trial of this size and scope. Instead NIAID said it will plan a smaller, more focused clinical trial designed to see whether the product has a significant effect on the amount of virus in a person's blood.

If an effect is found, then additional studies, or an expansion of the study could be carried out.

NIAID said it acted after reviewing the results of the STEP trial, a study of another vaccine that was halted last fall after reports of an increased number of infections among volunteers taking part in the test.

The agency said it still considers its vaccine scientifically intriguing and sufficiently different from other vaccines to proceed with the smaller trial.

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On the Net:

National Institute of Allergy and Infectious Disease: http://www.niaid.nih.gov