President-elect Joe Biden has picked a former Food and Drug commissioner to lead vaccine science in his drive to put 100 million shots into the arms of Americans in his administration's first 100 days and stem the COVID-19 pandemic.

Dr. David Kessler, who will have the title of chief science officer of COVID response, headed the Food and Drug Administration in the 1990s under presidents of both political parties. He has been acting as a top pandemic adviser to Biden and his appointment was announced Friday by the presidential transition office.

Kessler will work out of the federal Department of Health and Human Services, assuming responsibility for the scientific side of Operation Warp Speed, an effort launched under the Trump administration to rapidly develop vaccines and treatments. The drive has already produced two highly effective vaccines, and more are on the way.

Nonetheless, the nation's vaccination campaign has gotten off to a slow start, and most of the vaccine being delivered to states by the federal government is not being used right away.

A person advising the Biden transition team said Kessler will take on the role now being carried out by Dr. Moncef Slaoui, a prominent vaccine scientist and innovator who has been serving as chief advisor to Operation Warp Speed. Several vaccine candidates in the pipeline are in final clinical trials, and one company is expected to soon apply for FDA emergency approval for its formulation. The person spoke on condition of anonymity to discuss internal deliberations.

Kessler will coordinate vaccine review and approval, as well as the logistics of manufacturing millions more doses. Experts say the U.S. will need to vaccinate upwards of 250 million people to approach the goal of “herd immunity," where there is widespread resistance to virus allowing for a return to normal life. So far fewer than 12 million doses have been administered.