Half of adult Americans have now been fully vaccinated against Covid-19, the Biden administration said on Tuesday.
Joe Biden previously set a goal of having 70% of adults with at least one dose by 4 July. Vaccine hesitancy or resistance remains a problem, particularly among Republicans, with the rate of shots administered slowing.
Elsewhere on Tuesday, Moderna enhanced prospects of more vaccinations for younger Americans when it said its Covid-19 shot strongly protects children as young as 12.
Earlier this month, the US and Canada authorized a vaccine by Pfizer and BioNTech for use starting at age 12.
Releasing preliminary findings based on testing on more than 3,700 young people aged 12 to 17 in the US, Moderna said there were no Covid-19 diagnoses in children who were given two doses of its vaccine and four cases among those given dummy shots.
The Cambridge, Massachusetts company said the vaccine appeared 93% effective two weeks after the first dose.
The company also said its vaccine triggered the same signs of immune protection in children as it does in adults – and the same mild and temporary side-effects.
Officials said they intended to submit the data to the Food and Drug Administration and other global regulators early next month.
The White House has ramped up vaccine distribution as coronavirus cases and deaths have fallen. There are three vaccines in use and the US has increased the number of shots it is exporting.
In a statement issued as the Biden administration announced that 50% of US adults were not fully vaccinated, Donald Trump sought credit for progress against the pandemic, hailing “the record-breaking development of the vaccine and its early purchase and distribution by the Trump administration”.
Trump called Operation Warp Speed, an administration initiative which worked on vaccine development, “one of the greatest miracles of the ages”.
He also thanked members of his administration “who pushed so hard for a vaccine and got it done in less than nine months when everybody was saying it would take at least [three to five] years, and probably not happen”.