Former US President Barack Obama says he had tested positive for the coronavirus, though he's feeling relatively healthy and his wife, Michelle, tested negative.

"I've had a scratchy throat for a couple days, but am feeling fine otherwise," Obama said on Twitter. "Michelle and I are grateful to be vaccinated and boosted."

Obama encouraged more Americans to get vaccinated against the coronavirus, despite the declining infection rate in the US. There were roughly 35,000 infections on average over the past week, down sharply from mid-January when that average was closer to 800,000.

The Centers for Disease Control and Prevention (CDC) reports that 75.2 per cent of US adults are fully vaccinated and 47.7 per cent of the fully vaccinated have received a booster shot. The CDC relaxed its guidelines for indoor masking in late February, taking a more holistic approach that meant the vast majority of Americans live in areas without the recommendation for indoor masking in public.

According to the Reuters' Covid-19 tracker, Covid-19 infections are decreasing in the US, with 49,611 new infections reported on average each day.

There have been 993,749 deaths from Covid 19 in the US since the pandemic began. At least 55,926,001 have recovered from the disease.