WASHINGTON — 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 occurred 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.