Fully vaccinated people can safely engage in outdoor activities like walking and hiking without wearing masks but should continue to use face-coverings in public spaces where they are required, US health regulators and President Joe Biden said on Tuesday, while urging those who have not to get the shot.

The updated health advice comes as more than half of all adults in the United States have now received at least one dose of Covid-19 vaccine, according to the US Centers for Disease Control and Prevention (CDC).

Biden said the new advice was a result of steps the country had taken to fight the coronavirus.

"We’ve made stunning progress because of all of you," Biden said, adding that Covid-19 cases are "down dramatically." Deaths among senior citizens have dropped by 80% as vaccinations have increased, he said.

"If you're vaccinated, you can do more things, more safely, both outdoors as well as indoors," Biden said, while adding that masks should still be worn in big crowds and at stadium events.

Wearing face masks has been considered by experts one of the most effective ways of controlling virus transmission. With most Covid-19 transmission occurring indoors, and vaccinations on the rise, the use of masks outdoors has been under public debate for weeks in the United States as Americans look to enjoy the benefits of being fully vaccinated.

The CDC called the new guidelines a "first step" in helping fully vaccinated Americans resume activities they had stopped because of the pandemic.

New Covid-19 cases dropped 16% in the last week as the United States surpassed 140 million people having received at least one shot of authorized vaccines from Pfizer/BioNTech, Moderna or Johnson & Johnson's one-dose vaccine.

Just over 29% of the US population is fully vaccinated, the CDC reported, and 43% have had one dose of the two-shot vaccines.

Last week’s figures were the biggest percentage drop in weekly new cases since February, according to a Reuters analysis of state and county data.

The White House is trying to overcome vaccine hesitancy, and Biden offered the new mask guidelines as another reason to get the jab on Tuesday.

"So, for those who haven't gotten their vaccination, especially if you're younger or thinking you don't need it, this is another great reason to go get vaccinated," Biden said.

Small outdoor gatherings

The CDC said fully-vaccinated Americans can safely dine outdoors with friends from multiple households at restaurants and attend small outdoor gatherings with a mixture of fully vaccinated and unvaccinated people.

CDC continues to recommend masking for crowded outdoor events such as parades and sporting events and indoor visits to the hair salon, shopping malls, movie theaters and houses of worship.

The agency classified activities as "red," "yellow" and "green" based on level of safety for unvaccinated people.

It said unvaccinated people can also walk and run unmasked with household members outdoors safely and attend small outdoor gatherings with fully vaccinated family and friends.

Data on whether vaccinated people can spread infection to those who did not receive their shots is limited and the CDC warned that people should evaluate risk to friends and family before going out without masks.

This is an update to the CDC’s guidance, which in March said people who have been fully vaccinated against Covid-19 can meet without masks indoors in small groups with others who also have been inoculated.