President Joe Biden tested positive for COVID-19 on Thursday, is experiencing mild symptoms and has begun taking Paxlovid, an antiviral pill treatment.

A look at what we know about the president and his coronavirus infection:

HOW’S HE FEELING?

Biden is reporting a runny nose, fatigue and an occasional dry cough, according to a memo from Dr. Kevin O’Connor, the president’s doctor. Biden felt tired Wednesday evening and didn’t sleep well, White House COVID-19 coordinator Dr. Ashish Jha said at a press briefing. Biden tweeted Thursday: “Folks, I’m doing great. Thanks for your concern.”

WHAT KIND OF TEST DID HE USE?

Biden is routinely screened for coronavirus. His infection was detected first with an antigen test, the same type that many Americans use at home. It was then confirmed with a PCR test, the president’s doctor said. The president’s last previous test for COVID-19 was Tuesday, when he had a negative test result.

IS HE VACCINATED?

Yes. The president is fully vaccinated and twice boosted. Biden got two doses of the Pfizer vaccine shortly before taking office, a first booster shot in September and an additional dose March 30.

IS HE GETTING TREATMENT?

Biden is taking Paxlovid, which was authorized in the U.S. late last year. In older people and other high-risk patients, the drug was shown to reduce the chances of hospitalization or death from COVID-19. The pills work best if taken within five days of the start of symptoms. The president’s doctor said Biden’s vaccination status and early treatment with Paxlovid should keep him out of danger. Biden has temporarily stopped taking a blood thinner and a cholesterol drug as recommended for patients on Paxlovid.

WHAT’S THE ISOLATION PLAN?

Biden will work in isolation for at least five days and until he tests negative, the White House said. Once he tests negative, he will return to in-person work. The White House said it will provide a daily update on the president’s status.

HOW DOES THE VIRUS AFFECT OLDER PEOPLE?

At age 79, Biden is in a high-risk group for severe illness. About 8 in 10 COVID-19 deaths occur in people over age 65, with risk increasing with age. Also among the most vulnerable are those with other health issues such as diabetes and heart conditions.

DID HE GET THE BA.5 VARIANT?

It’s unclear which variant Biden has contracted, though a sample has been sent for genetic sequencing to determine that. The dominant virus variant in the U.S. is the omicron mutant BA.5, which is also prominent worldwide. The variant accounted for three-quarters of new infections reported in the U.S. last week. It’s also been gaining ground globally, making up more than half of sequenced omicron cases. Experts say BA.5 is one of the most transmissible variants yet but they haven’t seen an increase in severity compared with previous omicron variants.

WHERE DID HE CATCH IT?

That’s unclear. Symptoms can start two days to two weeks after exposure to the virus. Biden has kept a busy travel schedule lately. During his recent Middle East trip, the president was seen fist-bumping, handshaking and even occasionally hugging. He returned to Washington late Saturday and kept a low profile for the next three days, leaving briefly to attend church and for a Tuesday appearance outside the White House with Ukraine’s first lady. He traveled to Massachusetts on Wednesday to announce modest new steps to combat climate change.

WHAT ABOUT JILL BIDEN?

The first lady said Thursday that she tested negative earlier in the day. She will follow CDC guidance on masking and distancing during scheduled visits to Michigan and Georgia on Thursday, said Michael LaRosa, her spokesperson.

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AP Medical Writer Laura Ungar contributed.

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The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute’s Department of Science Education. The AP is solely responsible for all content.