WASHINGTON (AP) — President Joe Biden laid out hopeful new steps Monday to expand coronavirus vaccinations but also echoed the stern warnings of a top public health official who told Americans she has a recurring feeling of “impending doom” that a fourth wave of the virus may be coming.

“This is deadly serious,” Biden said, urging governors to reinstate mask mandates and other restrictions that some states have been easing.

Biden announced that by April 19 at least 90% of the adult U.S. population would be eligible for vaccination — and would have access to a vaccination site within 5 miles of home. Quick vaccination would still depend on supply.

Biden had previously directed that all states make all adults eligible for vaccination by May 1, but many have moved to lift eligibility requirements sooner in anticipation of supply increases.

Meanwhile, the White House is moving to double the number of pharmacies participating in the federal retail pharmacy program — which has emerged as among the most efficient avenues for administering vaccines — and increase the number of doses for them to deliver. Retail pharmacies are located relatively close to most Americans and have experience delivering vaccines like flu shots.

Biden announced that the U.S. is expecting delivery of 33 million doses of COVID-19 vaccine this week — including 11 million of the single-dose Johnson & Johnson shot.

More than one in five adults and nearly 50% of senior American are fully vaccinated, according to data from the CDC. On Thursday, the U.S. set new single-day record for shots in arms: more than 3.2 million.

“Now is not the time to let down,” Biden said. “Now’s not the time to celebrate. It is time to do what we do best as a country: our duty, our jobs, take care of one another.”

“Fight to the finish,” he added. “Don’t let up now.”

The White House, meanwhile is ruling out the creation of a national “vaccine passport” for Americans to verify their immunization status, saying it is leaving it to the private sector to develop a system for people show they’ve been vaccinated. Some other countries are establishing national databases to allow vaccinated people to resume normal activities.

“We do know that there is a segment of the population that is concerned that the government will play too heavy-handed of a role in monitoring their vaccinations,” said White House COVID-19 adviser Andy Slavitt. He said officials are worried that “it would discourage people” from getting vaccinated if the federal government was involved.

The administration, instead, is developing guidelines for such passports, touching on privacy, accuracy and equity, but the White House has not said when those guidelines will be ready.

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