WASHINGTON (AP) — President Joe Biden said the U.S. expects to take delivery of enough coronavirus vaccine for all adults by the end of May — two months earlier than anticipated — and he pushed states to get at least one shot into the arms of teachers by the end of March to hasten school reopenings.

Biden also announced Tuesday that drugmaker Merck will help produce rival Johnson & Johnson’s newly approved one-shot vaccine, likening the partnership between the two drug companies to the spirit of national cooperation during World War II.

Despite the stepped-up pace of vaccine production, the work of inoculating Americans could extend well into the summer, officials said, depending both on the government’s capacity to deliver doses and Americans’ willingness to roll up their sleeves.

Biden’s announcements quickly raised expectations for when the nation could safely emerge from the pandemic, but even as he expressed optimism, Biden quickly tempered the outlook.

“I’ve been cautioned not to give an answer to that because we don’t know for sure,” Biden said, before saying his hope for a return to normal was sometime before “this time next year.”

As Biden spoke, states across the country were moving to relax virus-related restrictions. This despite the objections of the White House and the nation's top infectious disease expert, Dr. Anthony Fauci, who have warned against any relaxation of virus protocols until more Americans are vaccinated.

In Texas, GOP Gov. Greg Abbott moved to lift his state’s mask-wearing mandate and a host of other limitations. Michigan’s Democratic Gov. Gretchen Whitmer eased capacity limits on restaurants and both public and residential gatherings.

Fauci has previously said the nation must achieve a vaccination rate of about 80% to reach “herd immunity." Only about 8% of the population has been fully vaccinated, according to the Centers for Disease Control and Prevention, though the pace of vaccination has been increasing.

The Biden administration has told governors to make preparations to administer even more doses in the coming weeks. More shots are also headed toward the federally backed program to administer doses in retail pharmacies, which federal officials believe can double or triple their pace of vaccination.

More than 800,000 doses of the J&J vaccine will be distributed this week to pharmacies, on top of the 2.4 million they are now getting from Pfizer and Moderna.

Those pharmacies will be key in getting the vaccines into the arms of teachers — particularly in the roughly 20 states where they have not been prioritized for shots. The aim is to help reopen schools to better educate students who have been at risk of falling behind during the pandemic and reduce the burden on parents who have had to choose between child care and a job.

"Let’s treat in-person learning as the essential service that it is," Biden said. Teachers will be able to sign up directly through participating retail pharmacies, the administration said.

White House press secretary Jen Psaki also announced Tuesday that the federal government was increasing supply of the Moderna and Pfizer vaccines to states next week to 15.2 million doses per week, up from 14.5 million previously. States will also receive 2.8 million doses of the J&J shot this week.

On a call with governors Tuesday, White House coronavirus coordinator Jeff Zients said states should prepare to administer 16 million to 17 million total weekly doses of Pfizer and Moderna vaccines by the end of March, climbing to 17 million to 18 million weekly by early April. The supply of J&J doses to states, expected to dip after the initial shipment this week, will climb to 4 million to 6 million weekly doses by the end of March and 5 million to 6 million doses weekly through the end of April.

Officials have said J&J faced unexpected production issues with its vaccine and produced only 3.9 million doses before being cleared for use on Saturday. J&J Vice President Richard Nettles told lawmakers on Capitol Hill last week that the company had faced “significant challenges” because of its “highly complex” manufacturing process.

Before the approval of the J&J shot, Biden had suggested that it would take until the end of July to have enough vaccine for every adult in the U.S.

Psaki said an "across-the-administration effort” was required to get the two historic rivals to work together on the vaccines, even though conversations between J&J and Merck have been going on for months.

“There’s a difference between conversations and it moving forward,” she said.

White House adviser Andy Slavitt said Wednesday that Biden was preparing for all contingencies to speed the vaccine supply, and that the new May timeframe was achievable.

“We are not in the habit of overpromising," he said.

The White House said Merck would devote two plants to the production process. One would make the vaccine and the other would handle inserting the vaccine into vials and ensuring strict quality controls. Psaki said the Biden administration was using its powers under the Defense Production Act to help Merck retool to work on the production.

The White House said the first doses produced with Merck's assistance would be available beginning in May. Federal officials have cautioned that setting up the highly specialized manufacturing lines to produce vaccines would take months.

Compared with the two-dose versions produced by Moderna and Pfizer, the J&J vaccine is less resource-intensive to distribute and administer, making it critical for U.S. plans to spread vaccinations around the world — but only once Americans are inoculated. The J&J vaccine can be stored for months at refrigerated temperatures, rather than frozen.

J&J has set up a global production network that includes brewing bulk vaccine at its Janssen facility in the Netherlands, and with a company in the U.S., Emergent BioSolutions, and another in India, Biological E. Ltd. Other contract manufacturers are lined up to help with later steps, including putting the vaccine into vials, in the U.S., Italy, Spain and South Africa.

In the scramble to create COVID-19 vaccines, the three Western drugmakers who’ve dominated the vaccine industry for decades — Merck & Co., Sanofi and GlaxoSmithKline — surprisingly all fell short. Merck halted its own plans to develop a coronavirus vaccine earlier this year, finding that its candidates were generating an inferior immune system response compared with other vaccines. It said it would instead focus its work on developing treatments for COVID-19.

Now, with a global clamor for more vaccine doses, those heavyweights are helping manufacture doses for less-experienced rivals whose vaccines won the first emergency authorizations from regulators.

Merck has since said it was in talks to help other drug companies with vaccine production, but wouldn’t say Tuesday whether other deals are imminent.

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Johnson reported from Fairless Hills, Pennsylvania. Lemire reported from New York. Lauran Neergaard in Washington and Rachel La Corte in Olympia, Washington, contributed to this report.