Paxlovid "rebound" patients may need longer treatment

Trial results showed that Paxlovid can reduce the risk of hospitalization and death from COVID-19 in high-risk patients by 89% if taken within five days of symptom onset. In some patients, however, virus levels and symptoms have rebounded after completing a course of Paxlovid, leading to concerns that variants might be developing resistance to the two-drug treatment or that the pills may somehow be weakening patients' antibody resistance.

But when researchers isolated the Omicron BA.2 variant from a rebound patient and tested it in lab experiments, they found it was still sensitive to Paxlovid and had no mutations that would reduce the drug's effectiveness. They also found their patient's antibodies could still block the virus from entering and infecting new cells.

The rebound of COVID-19 symptoms after Paxlovid treatment is likely happening because not enough of the drug is reaching infected cells to completely stop the virus from making copies of itself, the researchers said in a paper published in Clinical Infectious Diseases https://academic.oup.com/cid/advance-article/doi/10.1093/cid/ciac496/6611663. It is also possible that the drug may be metabolized, or processed, at different rates in different people, or that some people need to take it for more than five days.