US President Joe Biden on Thursday increased his government's Covid-19 vaccination goal to 200 million shots in his first 100 days in office.
"Today, I'm setting a second goal," Mr Biden said in the first press conference of his presidency.
"And that is we will, by my 100th day in office, have administered 200 million shots in people's arms."
The initial aim was for 100 million vaccinations in the first 100 days and his government met that goal weeks early.
The target was achieved in 58 days, meaning the next 100 million will have to be administered in six weeks.
"I know it's ambitious, twice our original goal, but no other country has come close. I believe we can do it," Mr Biden said.
He also said he was considering running for re-election in 2024.
"My answer is yes, I plan to run for re-election. That’s my expectation," Mr Biden said.
But he said had “never been able to plan four or three and half years ahead for certain”.
"I have no idea if there will be a Republican Party,” Mr Biden quipped.
Mr Biden also addressed the issue of migrants, including many unaccompanied minors, from Central America and elsewhere massing on the Mexican border, seeking asylum in the US.
More than 100,000 were received by the US Border Patrol in February, the most in about a year.
"There is a significant increase in the number of people coming to the border in the winter months of January, February, March. It happens every year," Mr Biden said.
He said migrants would be turned away but the US would allow unaccompanied children into the country.
"We are sending back the vast majority of the families that are coming," Mr Biden said. "They should all be going back.
"The idea that I'm going to say, which I would never do, if an unaccompanied child ends up at the border, we're going to let them starve to death and stay on the other side – no previous administration did that either, except [Donald] Trump.
"I'm not going to do it."
"I make no apologies for ending programmes that did not exist before Trump became president, that have an incredibly negative impact on the law, international law, as well as on human dignity."
On Wednesday, he appointed Vice President Kamala Harris to lead diplomacy with countries from which the migrants are coming: El Salvador, Guatemala, Honduras and Mexico.
He announced a plan with the Defence Department to add 5,000 beds at Fort Bliss in Texas for detainment on the border.
Mr Biden faced criticism for not holding a media conference earlier in his presidency, claiming he had not met goals for transparency.
Mr Trump held several earlier in his term, albeit free-wheeling and with attacks on media.
Mr Biden pledged that the US would have enough coronavirus vaccine supplies for all adults by the end of May, with the goal of returning "closer to normal" by July 4, Independence Day.
About 14 per cent of adults in the US are fully vaccinated and more than 25 per cent have had at least one dose, health authorities say.
The Centres for Disease Control and Prevention says the country has administered 130 million Covid-19 shots since the Pfizer-BioNTech and Moderna vaccines were approved in mid-December.
The US has also approved and administered the single-dose vaccine by Johnson & Johnson.
"I've been so impressed by the pace of vaccination," agency director Dr Rochelle Walensky said on Wednesday.
"So many Americans have embraced vaccination and have chipped in with their families and communities to help others get vaccinated.
"We are now vaccinating between 16 [million] and 20 million people a week, and this means that we are closer to resuming activities we love to do with those we care about the most."
States and local regions have their own eligibility requirements for vaccinations, with priority for inoculating the elderly, vulnerable people and essential workers.
Mr Biden has ordered states to open eligibility to all adults by May 1.
At least five states have met that goal already, with more than a dozen having plans to open eligibility in April. Others are weeks away.
Scientists and public health officials have suggested that the US would need at least 80 per cent of the population to be inoculated for herd immunity.
Some also advise that the threat of variants might increase that amount.
The US has had more than 545,000 deaths from Covid-19 and recorded more than 30 million cases.
Infections, hospital admissions and deaths have been on the decline since a peak in December and January, with new daily cases now about 55,000.
"I continue to be worried about the latest data and the apparent stall we are seeing in the trajectory of the pandemic," Dr Walensky said.
"CDC is watching these numbers very closely."