Former U.S. President Barack Obama said Sunday he had tested positive for the novel coronavirus but did not have serious symptoms, apparently because of vaccination.

"I just tested positive for COVID. I've had a scratchy throat for a couple days, but am feeling fine otherwise," the 60-year-old tweeted, adding his wife Michelle Obama had tested negative.

"Michelle and I are grateful to be vaccinated and boosted," said Obama, the first black president of the United States. "It's a reminder to get vaccinated if you haven't already, even as cases go down."

The most recent coronavirus surge triggered by the highly contagious Omicron variant is receding in the United States. Still, around 35,000 cases per day on average have been reported over the past seven days, according to data from the Centers for Disease Control and Prevention.

In the United States, 75.2 percent of adults have been fully vaccinated and 47.7 percent of them have received booster shots for further protection.