Dr. Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases, is promoting an ambitious and expensive plan to prepare for such nightmare scenarios. It would cost “a few billion dollars” a year, take five years for the first crop of results and engage a huge cadre of scientists, he said.

The idea is to make “prototype” vaccines to protect against viruses from about 20 families that might spark a new pandemic. Using research tools that proved successful for Covid-19, researchers would uncover the molecular structure of each virus, learn where antibodies must strike it, and how to prod the body into making exactly those antibodies.

“If we get the funding, which I believe we will, it likely will start in 2022,” Dr. Fauci said, adding that he has been promoting the idea “in discussions with the White House and others.”