Biden, CDC director warn of virus rebound if nation lets up

FILE - In this Feb. 11, 2021, file photo, registered nurse Marife Edquilang, left, administers a dose of Pfizer COVID-19 vaccine to Anthony Monroe during a vaccination drive at Texas Southern University in Houston. At least 11 states opened vaccine eligibility to all adults this week in a major expansion of COVID-19 shots for tens of millions of Americans amid a worrisome increase in virus cases and concerns about supply and demand for the vaccines. States opening eligibility to anyone ages 16 and older on Monday included Texas, Oklahoma, Louisiana, Ohio and Kansas. (Brett Coomer/Houston Chronicle via AP)

Chicago area residents head into a walk-in mass vaccination site Monday, March 29, 2021, across the street from the United Center, home to the Chicago Bulls and Blackhawks in Chicago. At least 11 states opened vaccine eligibility to all adults this week in a major expansion of COVID-19 shots for tens of millions of Americans amid a worrisome increase in virus cases and concerns about supply and demand for the vaccines. In Chicago, the vaccine will not be available to everyone until at least May 1 because the city does not have enough shots on hand. (AP Photo/Charles Rex Arbogast)

FILE - In this March 3, 2021, file photo, licensed vocational nurse Jelisa Stewart prepares a dose of the Moderna COVID-19 vaccine for farmworkers at a County of Santa Clara mobile vaccination clinic at Monterey Mushrooms during the coronavirus pandemic in Morgan Hill, Calif. In California, mobile clinics are helping to vaccinate farmworkers who may not have transportation to larger vaccination sites or who cannot navigate the state’s online signup portal. (AP Photo/Jeff Chiu, File)

President Joe Biden speaks during an event on COVID-19 vaccinations and the response to the pandemic, in the South Court Auditorium on the White House campus, Monday, March 29, 2021, in Washington. (AP Photo/Evan Vucci)

People wearing face masks as a precaution against the coronavirus wait in line to receive COVID-19 vaccines at a site in Philadelphia, Monday, March 29, 2021. (AP Photo/Matt Rourke)

President Joe Biden speaks during an event on COVID-19 vaccinations, in the South Court Auditorium on the White House campus, Monday, March 29, 2021, in Washington, as Vice President Kamala Harris listens. (AP Photo/Evan Vucci)

In this March 19, 2021, photo, Dr. Rochelle Walensky, director of the Centers for Disease Control and Prevention, leads President Joe Biden into the room for a COVID-19 briefing at the headquarters for the CDC Atlanta. Walensky is making an impassioned plea to Americans not to let their guard down in the fight against COVID-19. She warned on March 29 of a potential “fourth wave” of the virus. (AP Photo/Patrick Semansky)

Dr. Rochelle Walensky, director of the Centers for Disease Control and Prevention testifies during a Senate Health, Education, Labor and Pensions Committee hearing on the federal coronavirus response on Capitol Hill in Washington, Thursday, March 18, 2021. (AP Photo/Susan Walsh, Pool)

Chicago area residents pass between a drive-through and walk-in mass vaccination site Monday across the street from the United Center, home to the Chicago Bulls and Blackhawks in Chicago. At least 11 states opened vaccine eligibility to all adults this week in a major expansion of COVID-19 shots for tens of millions of Americans amid a worrisome increase in virus cases and concerns about supply and demand for the vaccines. In Chicago, the vaccine will not be available to everyone until at least May 1 because the city does not have enough shots on hand. (AP Photo/Charles Rex Arbogast)

WASHINGTON — President Joe Biden and a top health official warned Monday that too many Americans are declaring virus victory too quickly, appealing for mask requirements and other restrictions to be maintained or restored to stave off a “fourth surge” of COVID-19. The head of the CDC said she had a feeling of “impending doom” if people keep easing off.