New York, Jan 5 : US pharma giant Pfizer's antiviral drug Paxlovid (Nirmatrelvir-ritonavir) does not reduce the risk of developing long Covid for vaccinated, non-hospitalised individuals, according to a study. A team of researchers from Univesity of California San Francisco (UCSF) revealed that among Paxlovid users, a higher proportion of individuals with acute symptoms rebound and test-positivity than previously reported. The findings appeared in the Journal of Medical Virology. Paxlovid treatment for acute Covid-19 has been shown to be effective for high-risk unvaccinated individuals. But the effect of the treatment on long Covid risk, including whether it protects vaccinated people from getting long Covid, has been less clear. To explore, the team selected a group of vaccinated people who had reported their first positive test for Covid-19 between March and August of 2022 and who were not hospitalised. In December 2022, the two groups reported similar conditions. About 16 per cent of those treated with Paxlovid had long Covid symptoms compared to 14 per cent of those who were not treated with the medication. Commonly reported symptoms included fatigue, shortness of breath, confusion, headache, and altered taste and smell. Those who took Paxlovid and then went on to develop long Covid reported as many long Covid symptoms as those who were not treated with Paxlovid. A small percentage of people developed severe long-term Covid, and those who had received Paxlovid were just as likely to have severe long-term Covid symptoms as those who did not. Among individuals who experienced symptomatic improvement during Paxlovid treatment, 21 per cent reported rebound symptoms. And among those with rebound symptoms, 10.8 per cent reported one or more long Covid symptoms compared to 8.3 per cent without rebound symptoms. For participants who repeated antigen testing after testing negative and completing treatment, 25.7 per cent reported rebound test positivity. In total, 26.1 per cent reported rebound symptoms or test positivity. "We found a higher proportion with clinical rebound than previously reported but did not identify an effect of post-treatment rebound on long Covid symptoms," said Matthew Durstenfeld, a cardiologist and UCSF assistant professor of Medicine. "Our finding that Paxlovid treatment during acute infection is not associated with lower odds of long Covid surprised us, but it is consistent with two other rigorously conducted studies finding no difference in post-Covid conditions between 4 and 6 months after infection." The researchers, however, noted that the study may have been impacted by limitations arising from its observational nature with researchers relying on patient self-reporting of treatment and long Covid symptoms. /IANS