US President Joe Biden also announced on Wednesday that the country has hit 200 million Covid-19 shots, a target he had set out to meet by the end of April, Xinhua news agency reported.

Biden said the country is entering a new phase in its vaccination efforts as it starts to shift the focus from getting the vaccine to those most at risk to the general population.

"The time is now to open up a new phase of this historic vaccination effort," Biden said. "To put it simply, if you've been waiting for your turn, wait no longer. Now's the time for everyone over 16 years of age to get vaccinated."

About 215 million Covid-19 vaccine shots have been administered by Wednesday, while more than 277 million Covid-19 vaccine doses have been distributed across the country, CDC data showed.

Currently there are about 87 million Americans fully vaccinated, accounting for 26.4 per cent of the US population, according to CDC data.

About 134 million Americans received at lease one Covid-19 shot, accounting for 40.5 per cent of the population.

Among the fully vaccinated, 35 million are people 65 years of age or older, accounting for 65.6 per cent, CDC data showed.

The United States has been ramping up vaccine rollout since last December. There are three COVID-19 vaccines authorized for emergency use in the country.

The US Food and Drug Administration authorized the one developed by American drugmaker Pfizer in partnership with German company BioNTech, and another by American drugmaker Moderna, in December last year.

Johnson & Johnson's Covid-19 vaccine was approved for emergency use on February 27, but it was halted for use last week after rare blood clotting cases emerged in six recipients.

According to CDC data, currently a total of 113 million Pfizer/BioNTech doses and 94 million Moderna doses have been administered in the United States, while 7.9 million Johnson & Johnson shots have been administered before its pause.