US President Joe Biden announced on Tuesday that all adults should be eligible for the Covid-19 vaccine by April 19, bringing forward his May 1 deadline for all states and territories.
"By no later than April 19, in every part of this country, every adult 18 or over will be eligible to be vaccinated," Mr Biden said.
He made his remarks after a visit to a vaccination site in Alexandria, Virginia, just a short drive from Washington, DC.
"No more confusing rules. No more confusing restrictions," Mr Biden said. "Every adult is eligible to get in line."
Eligibility varied by state or territory, and largely gave priority to elderly and vulnerable at-risk populations such as the immuno-compromised.
Essential workers were also among the first groups vaccinated.
The accelerated pace of eligibility comes as supplies of the three federally approved vaccines – those developed by Pfizer, Moderna and Johnson & Johnson – have increased.
Mr Biden has promised there will be enough vaccines for all US adults by the end of May.
He says 150 million shots have been given in his first 75 days, and 200 million will be given when he reaches the 100th day of his presidency.
It surpasses his initial goal of 100 million vaccinations in 100 days.
On Monday, the Centres for Disease Prevention and Control registered 62 million people who have been fully vaccinated, along with more than 106 million who have had at least one dose.
"We're the first country to vaccinate over 62 million people," Mr Biden said.
The country is averaging about 3 million immunisations daily.
On Saturday, April 3, a record 4.1 million vaccines were administered in 24 hours.
The US vaccination programme is accelerating while the country is recording 63,000 cases daily, along with the spread of variants that are more transmissible or can cause severe illness.
Mr Biden's decision to move up the eligibility deadline may be influenced by growing concern that a fourth surge in cases is taking hold.
"We're making incredible progress," he said. "There's a lot of good news but there's also some bad news. New variants of the virus are spreading and they're moving quickly."
The White House Covid-19 Task Force has continued to advise caution amid weeks of rising cases after a dramatic decrease that came after the worst surge in winter.
"We aren't at the finish line, we still have a lot of work to do," Mr Biden said. "We're still in a life-and-death race against this virus."
Scientists say the country may need about 80 per cent of the population to be inoculated for herd immunity to be reached.
"We're not even halfway through vaccinating 300 million Americans," Mr Biden said, referring to the country's population. "This is going to take time."
He still hopes to have most US adults immunised by July 4, the nation's Independence Day holiday.
