(CNN) — President Joe Biden’s symptoms “continue to improve” after being diagnosed Thursday with COVID-19, the President’s physician said in a Saturday letter.

“His primary symptoms, though less troublesome, now include sore throat, rhinorrhea, loose cough and body aches,” Dr. Kevin O’Connor wrote. “His voice remains deep. His pulse, blood pressure, respiratory rate and temperature remain entirely normal. His oxygen saturation continues to be excellent on room air. His lungs remain clear.”

Biden completed his second full day of the Paxlovid on Friday night, and will continue to receive the antiviral drug, O’Connor said.

O’Connor wrote Biden’s “causative agent” is “most likely” the BA.5 COVID-19 variant, which he notes “is responsible for 75-80% of infections in the United States at this time.”

Biden will “continue to isolate in accordance with Centers for Disease Control and Prevention (CDC) recommendations,” O’Connor said, and being treated with oral hydration, Tylenol and low dose aspirin as an alternative type of blood thinner.

O’Connor said Biden, who had asthma when he was younger, will also continue to be treated with his albuterol inhaler “as needed,” which he has used a few times since testing positive.

White House chief of staff Ron Klain said later Saturday during brief remarks Biden was feeling “pretty well.” Biden has been participating in “virtual conference call meetings,” Klain said, adding, “He’s been on the phone.”

Klain did not respond when asked by CNN whether O’Connor would be speaking to reporters about the President’s condition in the coming days.

Dr. Anthony Fauci, the director of the National Institute of Allergy and Infectious Diseases, told CNN’s Amara Walker on Saturday morning, “We have a reason to believe that (Biden) will do very well.”

While he hadn’t spoken directly to the President, Fauci said he’s been in “very close contact” with O’Connor following Biden’s positive test result this week.

Fauci said Biden “has no trouble breathing at all right now” and using an inhaler is what Biden “does regularly, when he gets an upper respiratory infection.”

At 79 years old, Biden is at an increased risk for a more severe case of COVID-19 due to his age, but he’s fully vaccinated and twice boosted — which the CDC says reduces risk of hospitalization and death for older adults.

O’Connor has been providing written updates about Biden’s illness and health status but has yet to publicly answer questions about it.

The White House medical unit will continue monitoring Biden “closely,” O’Connor said.

First lady Jill Biden, who is a close contact to the President, tested negative for Covid-19 on Saturday, her spokesperson Michael LaRosa said. She is not experiencing any COVID-19 symptoms and remains at their home in Wilmington, Delaware.

Thursday marked “Day 0” of the President’s COVID-19 timeline, meaning he would be in isolation until at least Tuesday in accordance to the CDC’s guidelines.

But Fauci confirmed to CNN Saturday Biden would be leaving isolation once he tests negative for COVID-19, straying from CDC guidance.

“You have to really go by the circumstances that you’re in,” Fauci said. “The President is in a position to be able to test every day and wait till he becomes negative before he goes back. But that doesn’t mean that everyone has to do that.”

This story has been updated with additional information.

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