While Pfizer’s antiviral breakthrough pills are highly useful in keeping people with Covid out of the hospital, there are mounting reports that patients treated with Paxlovid for the coronavirus may experience a second bout shortly after recovery.

So far, there are few case reports about the rebound effect of the Pfizer drug, but the situation lights up a warning sign and points to the need for new research and analysis on the medication against covid-19. Eventually, the medication protocol, such as days of use, may be revised for some patients.

With mostly just anecdotal reports coming out, questions remain as to whether people whose Covid symptoms return shortly after they take Paxlovid are contagious and should keep isolating to avoid passing the virus to others.

Those who do encounter the second round of symptoms may be concerned about whether or not they should seek further treatment due to the abrupt change.

When the FDA issued emergency authorization for those at high risk of severe Covid in December, Paxlovid was prescribed. In a clinical experiment, a five-day course of prescription medicines lowered the chance of hospitalization or death by 88 percent. Since Paxlovid was approved, the federal government has supplied over 1.7 million courses to the states, fully covering the treatment. The White House announced on Monday that it will expand the number of locations where Paxlovid is available, citing the fact that many of the dosages have gone unused.

“There’s still so much we don’t know about Covid-19 and the best way to treat it,” says Dr. H. Clifford Lane, deputy director for clinical research and special projects at the National Institute for Allergy and Infectious Diseases. “These anecdotes give us reason to re-examine duration of therapy, approaches to therapy, other laboratory tests we might use to predict who could benefit from longer courses of treatment.”

Report on the rebound effect of Paxlovid

Published on the Research Square platform, a preprint — a non-peer-reviewed study — brought a case report on the rebound effect of the drug Paxlovid. The research was led by physician Michael Charness, chief of staff at the VA Boston Healthcare System, USA.

“Our findings suggest that viral replication and symptoms of covid-19 may return after very early treatment with NM/R [the drug, composed of the combination of nirmatrelvir and ritonavir] before natural immunity is sufficient to completely eliminate SARS- CoV-2”, say the study authors.

According to the doctors responsible for the case, a 71-year-old patient was “cured” of covid-19, after treatment with the drug Paxlovid. The individual is asthmatic – a condition that can facilitate the evolution of the disease to the severe form – and had already received the booster of the vaccine against covid-19.

Pfizer medication was started within the first few days of diagnosis and the patient reports that the symptoms have passed. However, “on day 9, still in isolation, he developed typical cold symptoms with rhinorrhea [nasal discharge], sore throat, runny nose and asthma; these peaked on day 10 and resolved on day 12,” according to the authors.

The patient’s samples underwent genetic sequencing and it was possible to prove that the case was not reinfection of the coronavirus. In addition, tests for other respiratory viruses were done, but he was only infected with the covid-19 virus.

“Further work is needed to determine the frequency, duration, and spectrum of rebound symptoms,” the study authors explain. 

In addition, it was not possible to know whether the condition occurs more often during treatment with the Pfizer drug than in patients not treated with the antiviral.

Another case

Michael Henry, a 31-year-old Philadelphia software developer who has been vaccinated and supplemented, first became unwell with Covid on April 4, when he developed chills and a fever.

Henry, who has medical issues that put him at risk for serious illness, received a Paxlovid prescription the next day from an urgent care clinic. He was “completely fine” within 48 hours. But, a week after his last dose, he became ill again, this time with milder cold-like symptoms, and stayed sick for roughly five days.

He sought clarification from his doctor, Philadelphia’s Covid information line, and a health insurance nurse.

“Everyone I talked to gave me different answers.”

It has only been since December that Paxlovid has been prescribed after the Food and Drug Administration gave an emergency authorization for those who are at high risk of severe COVID. In a clinical experiment, a five-day course of prescription medicines lowered the chance of hospitalization or death by 88 percent. Since Paxlovid was approved, the federal government has supplied over 1.7 million courses to the states, fully covering the treatment. The White House announced on Monday that it will expand the number of locations where Paxlovid is available, citing the fact that many of the dosages have gone unused.

“There’s still so much we don’t know about Covid-19 and the best way to treat it,” says Dr. H. Clifford Lane, deputy director for clinical research and special projects at the National Institute for Allergy and Infectious Diseases. “These anecdotes give us reason to re-examine duration of therapy, approaches to therapy, other laboratory tests we might use to predict who could benefit from longer courses of treatment.”

Kit Longley, a spokesman for Pfizer, said the company is continuing to “monitor data from our ongoing clinical studies of Paxlovid, as well as real-world evidence” related to occurrences of post-Paxlovid relapse.

People who encounter a rebound can report it to Pfizer’s webpage for reporting Paxlovid-related adverse events, according to Longley.

Pfizer representative Longley stated in a statement that in Paxlovid’s clinical trial, the rare incidences of the coronavirus rebounding soon after participants finished treatment happened at the same rate among those who received a placebo.

“We did not see an association between the observed viral load increase and subsequent severe disease,” Longley adds. “Although it is too early to determine the cause, this suggests the observed increase in viral load is unlikely to be related to Paxlovid.”

Should the recurrence of symptoms require isolation?

The CDC advises that patients who test positive for Covid isolate for at least five days, with the isolation ending five days following a 24-hour period of no fever. It is recommended that people who become seriously sick or who have a damaged immune system isolate for at least 10 days.

Calls for the CDC to clarify its isolation criteria for rebound cases were met with silence by CDC spokesperson Scott Pauley.

Paxlovid hasn’t necessarily failed patients whose Covid-19 symptoms resurface after treatment; it may have rescued them from hospitalization and death, according to health care providers.

Image Credit: Getty

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