Joe Biden’s age, 79, automatically puts him at increased risk of complications from Covid, but infectious disease experts expect the president – who has received two Covid booster shots and who is otherwise in relatively good health – recovers quickly.

Biden tested positive for Covid on Thursday and has mild symptoms including fatigue, a runny nose and a dry cough, according to a letter from Dr. Kevin O’Connor, the president’s physician.

“He is a healthy 79-year-old man who was diagnosed quickly, has mild symptoms, is vaccinated and is on antiviral treatment. We all expect a good outcome,” said Dr Arturo Casadevall , professor of medicine at the Johns Hopkins School of Medicine.

White House Covid response coordinator Dr Ashish Jha told a briefing that the president is “feeling great”, has no fever and has been working all morning.

“We expect he will continue to have mild illness and will be monitored for symptoms,” he said.

Biden tested negative for Covid on Tuesday, so experts believe he is in the early stage of the disease.

“It was likely exposed over the weekend,” said Yale Medicine infectious disease specialist Dr. Scott Roberts. “Omicron’s median incubation period is three days, so my guess is that if it tested positive today, it was likely exposed on Sunday.”

The amount of virus in a person’s body, or viral load, is highest when symptoms begin, he said. So once Biden’s symptoms start to improve, he said, that will be a good indicator that he’s on the mend.

Covid may be more risky for people aged 50 and over for several reasons, including that older people are more likely to have underlying health conditions. Vaccine protection also tends to be less robust in older people because the immune system weakens with age. Doctors will likely check Biden’s blood oxygen levels several times a day to watch for signs of pneumonia.

“It’s one of the most important things to measure to make sure you don’t develop more serious disease in the lungs,” said Dr. William Schaffner, an infectious disease expert at Vanderbilt University Medical Center.

He said the president was unlikely to develop pneumonia because omicron tends to cause upper respiratory illness.

“The virus gets deep into your throat and causes inflammation in those local tissues,” Schaffner said. “This irritation causes coughing, runny nose, sore throat.”

“I wouldn’t be surprised if he’s hoarse for a few days,” he added.

What’s next for Biden

Biden takes Paxlovid, an antiviral treatment consisting of three pills taken twice a day for five days. Disease experts believe the drug works better the earlier it is given.

“His viral load is probably already down on the Paxlovid, and I suspect at this point he will likely continue to improve,” Roberts said.

A minority of people who take Paxlovid see symptoms rebound soon after completing treatment. They can test positive again, but experts said in these cases the disease tends to come back milder and people don’t usually develop new complications. Roberts said doctors should know if Biden experiences a Paxlovid rebound within a day or two of stopping the drug.

Jha said Biden is taking Eliquis, a blood thinner, and Crestor, a cholesterol-lowering drug, both of which must be stopped while on Paxlovid treatment. Paxlovid contains a drug called ritonavir, which slows the rate at which the body breaks down drugs. Statins like Crestor are processed by the liver, so a slower metabolism can cause the drug to build up in the body.

Experts have said there’s a chance Biden will develop long Covid — symptoms that last several months or more — but that risk is diminished by the fact that he’s vaccinated, double-boosted and taking an antiviral.

“I think once his period of isolation is over, is a good thing to look for is to bounce back and be interactive again? Or does it take him a little longer, as it does for some people? said Dr. Cameron Wolfe, infectious disease expert and associate professor of medicine at Duke University School of Medicine.

There is no evidence to suggest that the predominant variant in circulation – BA.5 – causes more severe disease than earlier variants. It is, however, much more contagious and better able to evade immune protection from vaccines or previous infections. Still, vaccines and treatments like Paxlovid continue to work well against it, experts said.

Should Biden start to feel sicker, other treatment options are available, including supplemental oxygen, steroids and the antiviral remdesivir. A monoclonal antibody, bebtelovimab, has also been shown to be effective against BA.5.

These defenses were not available the last time a president had Covid.

“Think about when President Trump got it,” Casadevall said. “He hadn’t been vaccinated, there was no Paxlovid at the time, and he ended up being hospitalized. In just two years we will have vaccines available and we will have antivirals available. I think that’s something to celebrate.