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FDA says Paxlovid not linked to COVID rebound, authorizes bivalent shots for tots

San Francisco Chronicle 3/16/2023 Aidin Vaziri
That settles that: FDA says Paxlovid does not cause COVID-19 rebound. © Brontë Wittpenn/The Chronicle 2022

That settles that: FDA says Paxlovid does not cause COVID-19 rebound.

There is no clear association between Paxlovid and COVID-19 reinfections, Food and Drug Administration staff said in briefing documents released Tuesday.

In its analysis of the oral antiviral pill manufactured by Pfizer, the agency said the likelihood of a phenomenon known as “viral rebound” — symptoms and apparent infectiousness coming back after completing a five-day course of the drug — was roughly the same for people who took Paxlovid and those who did not. 

They added that reinfections are part of the natural course of the illness.

“Virologic and/or symptomatic rebound may occur as part of the natural progression and resolution of COVID-19 disease, irrespective of Paxlovid treatment,” the FDA wrote in documents released ahead of a Thursday meeting of its external advisers, who will vote on whether to give Paxlovid full approval for adult and pediatric patients at high risk of hospitalization or death.

About 10% to 16% of people infected with COVID-19 experienced symptom rebound, “with no evidence” the rate was higher in patients who received Paxlovid than among those who got a placebo. The strain of the virus did not make a difference in the results. 

Last year, doctors who prescribed Paxlovid told The Chronicle that rebounds appeared to be happening more in the real world than in Pfizer’s clinical trials -- which found that they occurred in 2% of participants who took the drug. But those reports were anecdotal and not analyzed in a large controlled study.

The association between Paxlovid and repeat infections gained additional attention after several high-profile people, including President Biden and former White House medical adviser Dr. Anthony Fauci, experienced rebound cases after completing a course of the antiviral.

Wednesday’s FDA report aimed to emphasize that there is no evidence to suggest that Paxlovid causes rebound infections and that the drug is living up to its promise of keeping people out of the hospital. In fact, the active ingredients, nirmatrelvir and ritonavir, work together to inhibit the replication of the SARS-CoV-2 virus in the body.

About 12 million courses of Paxlovid have been distributed to U.S. pharmacies since it was granted emergency use authorization in December 2021, according to federal data. About 8 million Americans have taken the drug. There are currently about 1.3 million doses available nationwide.

The use of Paxlovid was associated with a reduction of the risk of COVID-19 hospitalization or death by 44% among highly vaccinated Americans aged 50 and older, according to the results of a large study published in December in the Annals of Internal Medicine.

There is also preliminary evidence that Paxlovid may reduce the risk of ending up with long COVID after an initial infection.

Pfizer, which makes Paxlovid, said it is conducting two additional studies to better understand viral rebound.

In other news, the FDA on Wednesday also granted emergency use authorization to Pfizer’s bivalent booster shot for some children under 5 years old.  

Children 6 months through 4 years of age who were previously vaccinated with three doses of the company’s original formula vaccine more than two months ago are now eligible to receive a single booster dose of the omicron-targeted shot. 

“Today’s authorization provides parents and caregivers of children 6 months through 4 years of age who received the three-dose primary series with the monovalent Pfizer-BioNTech COVID-19 Vaccine an opportunity to update their children’s protection by receiving a booster dose with the Pfizer-BioNTech COVID-19 Vaccine, Bivalent,” Peter Marks, director of the FDA’s Center for Biologics Evaluation and Research, said in a statement. 

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