Dr. Fauci testifies

From left, Dr. Anthony Fauci, director of the National Institute for Allergy and Infectious Diseases, CDC Director Dr. Robert Redfield, Adm. Brett Giroir, director of the U.S. coronavirus diagnostic testing and FDA Commissioner Stephen Hahn testify before the Senate Health, Education, Labor and Pensions Committee on Capitol Hill in Washington, D.C., on June 30, 2020.

 KEVIN DIETSCH / Pool / Abaca Press / TNS

If most of the population is vaccinated against COVID-19, then the coronavirus wouldn’t have enough new hosts and the pandemic would burn out. That transformational phenomenon is known as “herd immunity.”

But the United States, like so many other countries, has limited vaccine supplies, slower than expected distribution, and relentlessly rising case numbers.