Some patients report Covid rebound after taking Pfizer antiviral pills

MORE than 2.8 million courses of Pfizer’s Covid-19 oral antiviral treatment Paxlovid have been made available at pharmacies around the US, with the Biden administration working to improve access to the drug.

As Paxlovid has become more widely used, some patients have reported that Covid-19 symptoms recurred after completing treatment and experiencing improvement.

Dozens of individuals have reported rebounding Covid-19 symptoms on social media or to the US Food and Drug Administration (FDA) after taking Paxlovid, but Pfizer suggests the experience is rare.

Pfizer has said that from more than 300 000 patients it is monitoring who received the five-day treatment, around 1-in-3 000 – about 0.03% – reported a relapse after taking the pills.

That is a lower rate than Pfizer saw in its Paxlovid clinical trial, where about 2% of participants experienced a rebound in viral levels after completing treatment.

The Pfizer trial suggested relapses may be a broader Covid-19 trend as a similar number of those who had received a placebo also had a rebound in viral load levels. The cause is not yet known. Some doctors have suggested that because the drug attacks the virus so quickly, some patients’ immune responses to Covid-19 may be muted, allowing the virus to replicate again.

Others have said there may be a not yet identified common characteristic among those who suffer a rebound.

Pfizer chief development officer William Pao said it may be related to the virus itself, not Paxlovid, since the phenomenon was found among patients who got the drug and those who did not.

The FDA has also said it is unclear whether rebounds are related to Paxlovid. It said last week that there was no evidence of benefit for taking a second five-day course of the pills or for a 10-day course.

Pfizer has suggested otherwise. Chief executive Albert Bourla has said patients and doctors had told Pfizer a second five-day course of Paxlovid had cleared the virus. Mikael Dolsten, the company’s chief scientific officer, recently said some immunocompromised patients “may carry this virus for a very, very long time,” and may need to take multiple courses.