The US will have enough coronavirus vaccines for every adult by the end of May, President Joe Biden has said.
This will be two months earlier than previously expected, but Mr Biden said the vaccination drive must be extended, too, and people convinced to take it.
And he warned people to “stay vigilant” because “this fight is far from over”, with new variants a major concern.
His caution is at odds with some states, which are relaxing restrictions in order to boost their economies.
Although there has been a sharp fall in cases since the start of the year, in some areas that drop has been levelling off, fuelling fears of another wave.
The US has recorded 28.7 million infections and 516,000 deaths related to Covid-19 since the pandemic began, according to Johns Hopkins University research.
More than 76 million vaccination doses have been administered – covering 15.3% of the population and the US remains on track to meet Mr Biden’s pledge of delivering 100 million Covid-19 vaccine doses in his first 100 days in office.
What was in Mr Biden’s latest announcement?
The president said that drug manufacturer Merck – which this year discontinued work on its own vaccine – would now be helping Johnson & Johnson to produce its newly approved one-shot drug.
“We’re now on track to have enough vaccine supply for every adult in America by the end of May,” he said, adding it was “the type of collaboration between companies we saw in World War Two”.
But the president acknowledged that supply was only one issue, with the nation needing to extend its vaccination drive and convince people to take the shots.
“We need vaccinators, people who put the shots in people’s arms, millions of Americans’ arms,” he said.
“Great news, but stay vigilant,” Mr Biden said. “It’s not over yet.”
Another key announcement was the pledge to give every teacher at least one shot by the end of March, and speed up the reopening of schools.
But on a general reopening, he was more cautious, saying he was unsure when a return to normal would be possible, although he did then say before “this time next year”.