US Vice President Kamala Harris on Saturday received a COVID-19 vaccine booster shot and urged Americans to follow suit.

"I got the booster shot, and I want to encourage everyone to do the same when you are eligible," Harris said after receiving her third dose of the Moderna vaccine at the White House.

"What we have said from the beginning: It's safe and free," she said.

Harris said that over 90 per cent of Americans in intensive care units or who have died of Covid were unvaccinated.

"So let's get vaccinated and we will get through the pandemic," she said.

Many Americans are still resisting vaccinations, with only 58 per cent of the population fully immunized. The United States has recorded over 745,000 deaths from COVID-19.

US health authorities have approved booster shots of the Moderna, Pfizer and Johnson & Johnson vaccines.

The boosters should be administered six months after the second dose to people aged 65 or older, as well as to people aged 18-64 who are either at high risk of severe Covid-19 or with frequent exposure to the virus due to the nature of their job.

57-year-old Harris had received her first two injections in December 2020 and January 2021, according to the White House. She is considered at risk of contracting Covid due to her official duties.

US President Joe Biden, 78, received his third dose of the vaccine in September.