COVID rebound after Pfizer treatment likely due to robust immune response, study finds

By Leroy Leo and Julie Steenhuysen

(Reuters) – A rebound of COVID-19 symptoms in some patients after taking Pfizer’s antiviral drug Paxlovid may be linked to a robust immune response rather than a weak one, U.S. government researchers reported on Thursday.

They concluded that taking longer treatment – beyond the recommended five days – was not necessary to reduce the risk of recurrence of symptoms, as some have suggested, based on intensive investigation. on rebound in eight patients from the National Institutes of Health’s. Clinical Center.

All patients in the study had developed robust immune responses, but researchers found higher levels of antibodies in patients who rebounded.

The team said their data runs counter to the hypothesis that impaired immune responses are the reason symptoms return in some patients.

“Our results suggest that a more robust immune response rather than uncontrolled viral replication characterizes these clinical rebounds,” the team wrote.

The study, published in the journal Clinical Infectious Diseases, follows numerous reports from individuals who took Paxlovid as recommended within five days of infection and saw a return of symptoms after completing the five-day course. .

President Joe Biden and National Institute of Allergy and Infectious Diseases Director Dr. Anthony Fauci both experienced a COVID rebound after taking the drug.

The cases raised concerns that Pfizer’s two-drug antiviral treatment could interfere with the development of a long-lasting immune response.

The study involved six people whose COVID symptoms returned after taking Paxlovid, and two with rebound symptoms after apparent recovery who did not take the pills. Their responses were compared to a group of six people who had COVID but did not experience a rebound. All of the volunteers had been vaccinated and boosted and all were infected with some version of the Omicron variant of the virus.

The blood of the study volunteers was intensively surveyed to assess their immune response during the acute infection phase and the rebound phase.

All rebound patients had experienced significant improvement in their symptoms prior to their rebound. Of those who rebounded from Paxlovid, four had milder symptoms than when they were initially infected, one had the same level of severity, and one reported more severe symptoms.

None of the rebound patients required further treatment or hospitalization.

Rebound symptoms may be partially driven by a robust immune response to residual virus in the airways, the study authors suggested. They concluded that the drug does not hamper the immune response in some individuals, as some had feared.

Larger, more detailed studies are needed to better understand COVID symptom rebound, the research team said, adding that current data supports the need to isolate such patients.

The researchers also suggested that there is still a need to evaluate longer courses of Paxlovid in immunocompromised people where the immune response may be ineffective.

(Reporting by Leroy Leo in Bengaluru and Julie Steenhuysen in Chicago; Editing by Bill Berkrot)

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