(NewsNation) — President Joe Biden tested positive for COVID-19, the White House announced Thursday morning.

Biden, 79, is fully vaccinated, twice boosted and experiencing very mild symptoms, press secretary Karine Jean-Pierre said in a statement. A letter from Biden’s doctor, Kevin C. O’Connor, said Biden has a runny nose and fatigue with an occasional dry cough that started Wednesday evening.

“Folks, I’m doing great. Thanks for your concern,” Biden tweeted Thursday. “Keeping busy!”

There seemed to be a lack of clarity, however, on when Biden’s symptoms started. O’Connor’s letter indicated all of Biden’s symptoms began Wednesday night, but Jean-Pierre and White House COVID-19 coordinator Dr. Ashish Jha said the president’s only symptom Wednesday night was fatigue.

Jha said to his knowledge Biden experienced fatigue on Wednesday night, accompanied by a restless night of sleep. He said Biden woke up Thursday morning and upon speaking to his doctor, also said he was experiencing a runny nose and dry cough.

“I think he became aware of his symptoms this morning,” Jha said. He went on to further lament he could not say “exactly when” Biden began to feel symptoms.

Jean-Pierre said it was her understanding Biden felt “totally normal” Tuesday and Wednesday, before feeling fatigued Wednesday evening.

CDC guidance calls for anyone experiencing COVID-19 symptoms to begin isolating, even before they have tested positive for the virus.

In a video posted on social media titled “An update from me,” the president said,” I’m doing well, getting a lot of work done. Going to continue to get it done. And in the meantime, thanks for your concern. And keep the faith. It’s going to be okay.”

Vice President Kamala Harris, who was with the president on Tuesday, tested negative for COVID-19. Her schedule will continue as planned.

Biden has begun taking the leading COVID-9 pill Paxlovid, an antiviral drug designed to reduce the severity of the disease, Jean-Pierre said. Paxlovid, which is produced by Pfizer, has been proven to bring about a 90% reduction in hospitalizations and deaths among patients most likely to get severe symptoms.

As of now, the president will isolate at the White House for at least five days and continue his duties from there.

“He has been in contact with members of the White House staff by phone this morning, and will participate in his planned meetings at the White House this morning via phone and Zoom from the residence,” Jean-Pierre said.

Biden will continue isolating until he tests negative.

Dr. Timothy Quinn, Medical Director at Quinn Healthcare, spoke to NewsNation’s “Rush Hour” about the president’s diagnosis. Dr. Quinn explained what President Biden’s doctor will be looking for as he treats the virus.

“Right now, it seems like the treatment is right on course. He’s receiving the new antiviral that’s specific for coronavirus, and it’s very effective. Mainly his physician will be looking out for symptoms. So far, his symptoms are very mild, which is a good sign. But because of his advanced age of 79, he will be watched a little more closely than maybe someone that’s a little bit younger. The fact that he’s been vaccinated and boosted is definitely in his favor,” Dr. Quinn explained.

The White House plans to provide a daily update on the president’s status, and will inform close contacts of the president about his diagnosis, including members of Congress and the press.

Up to this point, Biden has been able to avoid getting the virus, even as waves of it swept through Washington’s political class, including Harris, Cabinet members, White House staffers and lawmakers. Other world leaders have gotten the coronavirus as well, including British Prime Minister Boris Johnson and French President Emmanuel Macron.

Former U.S. President Donald Trump contracted the virus in October 2020, albeit in a far different time when vaccines were not available and treatment options were limited.

Biden has increasingly demonstrated in recent months a willingness to travel and participate in larger, indoor events where people are not wearing masks, even though these are riskier activities for contracting the virus.

In an April 30 speech to more than 2,600 attendees at the White House Correspondents’ Association dinner, Biden acknowledged the risks of going to large events, but said it was worthwhile to attend.

“I know there are questions about whether we should gather here tonight because of COVID,” he said. “Well, we’re here to show the country that we’re getting through this pandemic.”

White House officials said Biden was intent on showing he can fulfill his presidential responsibilities without fear of the virus, believing he was well protected against severe outcomes.

“His doctors are comfortable that he could continue to carry out his duties because of all these steps and precautions and protections he’s taken,” former press secretary Jen Psaki said on April 8.

After more than two years and over a million deaths in the U.S., the virus is still killing an average of 353 people a day in the U.S., according to the Centers for Disease Control and Prevention. Those who are unvaccinated are at far greater risk, the CDC said, and are two times more likely to test positive and nine times more likely to die from the virus than those who received at least a primary dose of the vaccine.

In recent weeks, U.S. officials have called for the public to exercise caution over the coronavirus as the BA.5 variant emerges.

“We should not let it disrupt our lives,” Dr. Anthony Fauci, the nation’s top infectious disease expert said July 12, “but we cannot deny that it is a reality that we need to deal with.”

First lady Jill Biden, who is in Detroit, tested negative for COVID, saying in a tweet that the president is feeling fine.

This story is developing and will be updated.

The Associated Press contributed to this report.