(NewsNation) — Dr. Anthony Fauci, President Joe Biden’s chief medical adviser, disclosed that he had a rebound of his COVID-19 symptoms after taking the drug Paxlovid.

Paxlovid is an antiviral therapy produced by Pfizer and the pill Biden took after initially testing positive for COVID-19.

Fauci said his symptoms after taking the drug were, in fact, worse than his original symptoms.

To date, similar cases of so-called “Paxlovid rebound” have been limited to small studies and anecdotes shared on social media.

Dr. Yalda Safai, global medical & health journalist, joined NewsNation’s “Rush Hour” to discuss the occurrences where patients, who initially feel better after taking the drug, have symptoms and sometimes even a positive test after finishing treatment.

“This drug is not meant for everybody up to this point,” Safai said. “The FDA gave authorization for it for a specific population.”

According to Safai, Paxlovid is authorized for those over the age of 65 and anybody over the age of 12, that has an underlying condition like cancer, obesity, respiratory problems and diabetes.

“About 89% of people who take this drug, it’s helped lessen the chance of progressing to a severe illness,” Safai said. “So it’s doing its job.”

Despite its effectiveness, the Centers for Disease Control and Prevention acknowledged a rebound of COVID-19 symptoms may happen. The agency issued an advisory in May that patients may again have symptoms and a positive test within two to eight days of finishing their Paxlovid series.

The CDC noted that “a brief return of symptoms may be part of the natural history of” coronavirus infection in some people, regardless of Paxlovid treatment and vaccination status.

“There is a chance of rebound COVID,” Safai said about taking Paxlovid. “But still, the benefits in this case outweigh the cost.”

Paxlovid became a popular treatment due to its effectiveness and its convenience — because it can be taken in pill form and can be taken at home.

The CDC added that Paxlovid “continues to be recommended for early-stage treatment of mild to moderate COVID-19 among persons at high risk for progression to severe disease.”

Fauci ultimately took a second round of Paxlovid, which the CDC has not determined to be necessary if patients experience a rebound of symptoms.

When rebound symptoms occur, the CDC recommends isolating again for at least five days.

“I think there is understandable confusion when people hear about people rebounding,” Fauci told the New York Times. “Don’t confuse that with the original purpose of what Paxlovid is meant for. It’s not meant to prevent you from rebounding. It’s meant to prevent you from being hospitalized. I’m 81 years old, I was at risk for hospitalization and I didn’t even come close to being sick enough to be hospitalized.”

Fauci said that his Paxlovid treatment is working and that his symptoms are improving.

Watch the full interview with Dr. Yalda Safai in the video player at the top of the page.

The Hill contributed to this report.