Paul Clasby, of Holliston, Mass., left, receives his second shot of Moderna COVID-19 vaccine from paramedic Jake Lees, of North Attleborough, Mass., right, at a mass vaccination clinic, Wednesday, May 19, 2021, at Gillette Stadium, in Foxborough, Mass. (Photo: AP)

Half of all US adults have now received full Covid-19 vaccines, the White House said Tuesday, marking another huge milestone in the fight against the pandemic.

"Now 50% of all American adults are fully vaccinated," tweeted Cyrus Shahpar, Covid-19 data director for the White House.

That means half the adult population has received either two doses of the Moderna or Pfizer/BioNTech vaccines, or one of the single-dose Johnson & Johnson.

More than half a million Americans have died from the coronavirus but the country is now a world leader in rolling out vaccinations.

The US has reached almost 50 percent of its total population of 332 million with at least one dose, but its vaccination campaign has been slowing in the face of hesitancy.

President Joe Biden has set a target of having 70 percent of adults vaccinated with at least one dose by July 4. The current figure is almost 62 percent.