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A rebound of symptoms after taking a course of the COVID-19 antiviral pill Paxlovid may be the result of a robust immune response, not a weak one, according to a small study from the National Institutes of Health.

Investigators examined clinical outcomes data and lab tests from eight patients involved in a larger clinical trial who experienced a recurrence of COVID-19 symptoms and/or a new positive viral test after having tested negative. They found no evidence to suggest that these patients were infected with a SARS-CoV-2 that was resistant to Paxlovid. There was also no evidence of delayed development of antibodies. 

In fact, the rebound patients had a more robust immune response when compared to patients who had early acute COVID-19 and did not experience rebound, the researchers reported.

The results also support previous evidence that patients experiencing rebound who are symptomatic should isolate to keep from spreading the virus. Viral cultures detected infectious SARS-CoV-2 in one out of the eight rebound participants.

All participants were previously vaccinated and boosted against COVID-19. None had severe disease or required hospitalization during either acute infection or rebound.

The study was published in Clinical Infectious Diseases.

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