What is Paxlovid, the antiviral COVID treatment Biden took before his ‘rebound’ infection?

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President Biden tested negative for COVID-19 on Saturday, a day after he tested positive for the virus on what was the seventh day of his “rebound” infection. While the White House physician Kevin O’Connor said Biden “continues to feel very well," he is quarantining until he tests negative for a second time, out of an "abundance of caution."

The president first tested positive for COVID on July 21 and experienced mild symptoms. He took the five-day course of Pfizer’s antiviral drug Paxlovid and soon tested negative for the virus, clearing him to leave isolation. But around three days later, he tested positive once again.

Doctors say Biden is suffering a so-called “rebound” infection that is seen in a small percentage of people who take Paxlovid to treat COVID. The drug was authorized by the Food and Drug Administration in December.

What is Paxlovid?

According to the FDA, Paxlovid is an antiviral medication used to treat mild to moderate COVID-19 in adults and children ages 12 and older who weigh at least 88 pounds. Paxlovid is administered in three tablets, consisting of two medicines: two tablets of nirmatrelvir and one ritonavir tablet. The tablets are “taken together orally twice daily for five days, for a total of 30 tablets.”

A doctor holds up a package of the antiviral drug Paxlovid
A doctor holds up a package of the antiviral drug Paxlovid, which President Biden took for treatment after testing positive for COVID-19 last month. (Jennifer Lorenzini/Reuters)

O’Connor said in a memo this week that Biden’s cough was “almost completely resolved,” and that he continued to feel very well despite his rebound COVID-19 infection.

Why did the rebound occur?

In a series of tweets last week, White House COVID-19 coordinator Dr. Ashish Jha said “treatments like Paxlovid are designed to prevent serious illness. And they are doing that. Very well.”

He goes on to explain that in a Paxlovid rebound, “You get infected – get better (symptoms get better, antigen test negative) – then get worse. Could be new symptoms. Or it could be testing positive again – as the President has done.”

How often does rebound happen?

Jha said that according to data his team has been tracking from health systems, Paxlovid rebounds range “from 0.5% to 10%.”

The White House coordinator said it’s “important” to pay attention to rebound cases, “because when you rebound, you can potentially be contagious.” He added, however, that rebounding Paxlovid cases do “not seem to lead to serious illness (i.e. hospitalization, etc.), and that's key.”

President Biden speaks at a podium outside the White House.
President Biden speaking from a safe distance at the White House on Friday. (Evan Vucci/Pool/Reuters)

Dr. Anthony Fauci, the nation’s top infectious disease expert, said on MSNBC last week, "When you look at the studies, [rebound] generally does not occur very often.”

Fauci said that when he tested positive for the virus in June, he also experienced a COVID rebound after taking Paxlovid, with symptoms like a sore throat, runny nose and fever.

What are Biden’s rebound symptoms?

When he first tested positive during his rebound, Biden experienced no new symptoms, according to White House officials, who said he “tested positive on a routine test.”

This week, O’Connor said Biden was “still experiencing an occasional cough,” but on Friday, it was nearly gone. By Saturday, Biden tested negative for COVID.

Biden’s “temperature, pulse, blood pressure, respiratory rate and oxygen saturation remain entirely normal,” the White House physician said. “His lungs remain clear.”

In his Twitter thread, Jha said that because Biden is president, he is continuing to be tested after recovery, which Jha called “unusual” and “not what most Americans do.”

“We don’t know how often that happens," for people who both do and do not take Paxlovid, he said, and become "positive again after testing negative. Because we don’t have a lot of people testing after recovery. But we know from the clinical trials it happens.”

Who is eligible for Paxlovid, and should you take it?

Dr. Ghazala Sharieff, chief medical officer of acute care at Scripps Health, said not everyone who tests positive for COVID will be prescribed Paxlovid. Those who are eligible must test positive and have experienced symptoms within five days or less, and also be at higher risk for developing severe COVID symptoms.

Jha said that people at higher risk, for example those over 50 years old or who have chronic diseases, should get Paxlovid, because “it’ll dramatically reduce your risk of getting hospitalized or dying.”

Jha said the “bottom line” is that “Paxlovid is saving lives. Therapeutics are an essential part of fighting this pandemic. And way too many Americans are still dying of COVID. And when it comes to treatments like Paxlovid and monoclonals, we need to be using more of it, not less.”