SEATTLE, July 19 — The Bill and Melinda Gates Foundation awarded more than a quarter of a billion dollars today to researchers in 19 countries to speed the lagging development of an H.I.V. vaccine.

The grants are the largest private investment in making such a vaccine, the foundation said. They represent a significant shift in emphasis, to large-scale collaborative projects instead of small teams of researchers working independently.

The money will be given over five years to 16 scientific teams, including two New York groups. The scientists applied for the grants before Warren E. Buffett announced last month that he was giving $31 billion to the Gates Foundation.

The Gates Foundation has made development of an effective vaccine against H.I.V., the virus that causes AIDS, a major goal, and the new grants bring to $528 million the foundation’s investment for this purpose. By contrast, the National Institutes of Health has spent $3.4 billion since the 1980’s to develop a vaccine.