Pfizer’s Covid drug could have a rebound effect, report suggests

To prevent cases of covid-19 from becoming serious, the American pharmaceutical Pfizer developed the drug Paxlovid. In pill form, the antiviral prevents the SARS-CoV-2 coronavirus infection from evolving. However, rare reports begin to emerge that the medication can cause a rebound effect. In other words, after treatment and the patient’s apparent recovery, the disease may return.

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.

In Brazil, the National Health Surveillance Agency (Anvisa) approved the Pfizer drug at the end of March this year. In the world, countries such as the United States, Canada and China have also granted authorization to use this pill.

Report on the rebound effect of Paxlovid

Published on the platform Research Squarea preprint — study without peer review — brought a case report on the rebound effect of the drug Paxlovid. The research is 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 [o medicamento, composto pela combinação do nirmatrelvir com o ritonavir] before natural immunity is sufficient to completely eliminate SARS-CoV-2”, say the study authors. Because of this, the disease can “come back” a few days later.

understand the search

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. [secreção nasal], sore throat, runny nose and asthma; these peaked on day 10 and resolved on day 12”, the researchers detail.

The patient’s samples underwent genetic sequencing and it was possible to prove that the case was not a 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 is not possible to know whether the condition occurs more often during treatment with the Pfizer drug than in patients not treated with the antiviral.

Pfizer explains that cases are rare

Following the reports, Pfizer spokeswoman Kit Longley explained that the company continues to “monitor data from our ongoing clinical trials of Paxlovid, as well as real-world evidence” related to cases of post-Paxlovid relapse, according to the channel. NBC News.

In fact, some rare cases of the rebound effect of the medication were identified during the placebo-controlled clinical study. The trend was greatest between days 10 and 14 of the onset of symptoms of covid-19. However, the rate was similar to that of those who received a placebo.

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

Source: NBC News and Research Square