The exact cause is unknown. It may be due to virus reservoirs in tissues that are not reached by the medication, or reinfection. In May 2022, Pfizer suggested repeating the treatment, but the FDA said there has been no evidence of benefit.In a 2022 US case report of 10 people with rebound while the Omicron variant has been circulating, viral load during relapse was comparable to levels during initial infection and high enough to cause secondary transmission. Also, sequencing of SARS CoV2 in three patients showed that rebound was a relapse with the same strain as it was not due to a mutation during treatment nor an infection with a different viral strain. As of September 2022, it is unknown how common rebound is among people after Paxlovid treatment, but study author David Ho thinks it is not uncommon. Besides him, President Joe Biden, First Lady Jill Biden, Anthony Fauci and Peter Hotez are known to have experienced rebound. As of September 2022, Pfizer is studying the phenomenon in a new trial it calls EPIC-SR (standard risk) while the omicron variant is circulating.As of July 2022, no Paxlovid drug resistant SARS CoV2 has been observed in clinical context. The engineering of a nirmaltrevir-resistant chimera of Vesicular Stomatitis Virus under laboratory conditions was published without formal peer review in July 2022. Manufacturing
Pfizer selected its largest oral tablet factory in Freiburg as the launch facility for the manufacturing of the co-packaged medication.
In Germany, paxlovid is by prescription through physicians only and German physicians have been reluctant to prescribe it. Hence health minister Karl Lauterbach decided that general practitioners can stock 5 Paxlovid courses in their practice and dispense it directly to patients, that a prescription would be remunerated with 15 euros and that every nursing home should appoint a vaccination officer as well as a Paxlovid officer. As of August 2022 the treatment guidelines, which German family doctors follow, have not been updated since February 2022 and recommend Paxlovid only in unvaccinated risk patients, i.e. in only a few people.As of April 2022, the United States ordered a total of 20 million Paxlovid courses. As of July 2022, the United States Department of Health and Human Services set up at least 2,200 sites where people could receive Paxlovid as soon as they test positive for the virus, including pharmacies, community health centers and long-term care facilities. In July 2022, the US FDA allowed state-licensed pharmacists to prescribe it to people with COVID-19 at high risk of progressing to severe disease. Comparison to ivermectin
The co-packaged medication is sometimes falsely claimed to be a repackaged version of the antiparasitic drug ivermectin, which has been promoted as a COVID-19 therapeutic. Such claims, sometimes using the nickname "Pfizermectin", rely on superficial similarities between the mechanism of action of both drugs and the claim that Pfizer is suppressing the benefits of ivermectin. References
External links
Halford B (January 2022). "How Pfizer scientists transformed an old drug lead into a COVID-19 antiviral".