In rare cases with the antiviral Paxlovid the symptoms of Covid can recur after recovery

In rare cases, patients treated in the early stages of Covid withantiviral from Pfizer Paxlovid may have one relapse of the disease shortly after healing.

Who uses the Paxlovid

The phenomenon is observed in a limited number of patients treated and with relapses with different contours: the symptoms in the rebound of the disease can be worse, minor or similar to those felt before taking the medicine.
In Italy, the Medicines Agency (Aifa) has recently also given to general practitioners the possibility of prescribing oral antivirals for Covid, including Paxlovid, which is recommended (under emergency authorization) for anti Covid therapy in adults that do not require supplemental oxygen e have an increased risk of serious illness. Paxlovid should be administered as soon as possible and in any case within 5 days of the onset of symptoms and the therapy lasts for 5 days. Just after this lapse of time, the relapses occurred which also showed, with the tests, a return of positivity (in some cases with high viral load) after negativization during treatment with the medicine.

Reported in 2% of people in the study

In fact, the scientific documentation on post-Paxlovid relapse was already contained in Pfizer’s application for emergency use authorization (obtained in Europe on January 22nd): where it was stated that in the placebo-controlled clinical trial – which included 2,246 participants – several subjects appeared to have a relapse of SARS-CoV-2 RNA levels around day 10 or day 14 after the start of treatment. Pfizer has supplied to American NBC the figures relating to the total number of cases in the clinical study which were approx 2% of the participants (compared to approximately 1.5% relapses occurred in those who received placebo). It is not yet known whether the relapse rate is higher than this 2% in clinical practice, but scientists in the US (where the issue was raised) are pushing for federal agencies to clarify how patients and healthcare professionals should respond to this eventuality.

The open questions

Should people who are re-positive or who still experience symptoms isolate themselves? Are they contagious? Dr. Paul Sax, an infectious disease specialist at Harvard Medical School in a post on the April 25 blog on NEJM Journal Watch states: In my opinion we should assume that people who experience symptomatic relapse with a positive antigen test can pass the virus on to others. Those experiencing a second phase of symptoms (and were already considered vulnerable people) might think of a second course of treatment. In the US, the federal drug agency, the FDA, and Pfizer have made it clear that people with relapse are indeed eligible for the new treatment under the emergency use authorization the pill received. A Pfizer spokesperson, Kit Longley, said the drug maker is considering launching studies on Paxlovid treatments longer.

The reasons for the relapses: hypotheses

But why does the relapse occur? The good news for now it seems it’s not about drug resistance developed by the virus: there is no sign of this. Among the hypotheses is one that supposes that early suppression of the virus could impair the response of the immune system infection, or the idea that some people might do not absorb Paxlovid with the same effectiveness of others, or finally that the body could host the coronavirus in places that Paxlovid would have difficulty accessing and after the interruption of the treatment the small reserves of the virus could cause the relapse.
In the meantime, monitoring is intensifying and the scientists hope that observational studies will also be conducted to evaluate the frequency with which this relapse phenomenon occurs in the real world.