New York, Aug 3 (IANS): While there are reports of viral RNA and symptom rebound in people with Covid-19 treated with Pfizer's Paxlovid, a study led by Indian-origin scientists showed that even without the antiviral treatment both symptoms of Covid as well as viral load can retake in about one in three.

The study, not peer-reviewed yet and posted online on a preprint site, showed that 12 per cent of participants had viral rebound, meaning they tested positive again several days after testing negative.

Symptom rebound occurred in 27 per cent of participants after initial symptom improvement and in 10 per cent of participants after initial symptom resolution.

"Viral RNA rebound or symptom relapse in the absence of antiviral treatment is common, but the combination of high-level viral and symptom rebound is rare," Rinki Deo and Manish C. Choudhary from Brigham & Women's Hospital at Harvard Medical School in the US wrote in the paper, along with other scientists.

The team studied 568 participants. Anterior nasal swabs were collected for SARS-CoV-2 RNA testing on days 0-14, 21 and 28. Participants recorded the severity of 13 targeted symptoms daily from day 0 to 28. Viral rebounders were older than non-rebounders (median 54 vs. 47 years).

"It happens all the time. People who are untreated with Covid who then feel better can get symptoms afterward," co-author Dr. Davey Smith, chief of infectious diseases and global public health at the University of California, San Diego School of Medicine, was quoted as saying to NBC news.

Yet the 27 per cent was higher than what he'd expected based on anecdotal evidence, Smith noted.

Anyone who has had Covid could see a return of symptoms after they've initially gone away, and those symptoms could be worse or not as bad as the first bout, Smith said.

"It's just the variability in the natural course of the infection."

According to the US Centres for Disease Control and Prevention, there is a possibility of symptom recurrence in untreated Covid patients.

"A brief return of symptoms may be part of the natural history of SARS-CoV-2 (the virus that causes Covid-19) infection in some persons, independent of treatment with Paxlovid and regardless of vaccination status," the agency has said.

However, the CDC also issued a health alert in May informing physicians about Paxlovid rebounds

The rebound in symptoms has been more frequently documented among people who have taken the Paxlovid pill consisting of nirmatrelvir and ritonavir tablets, co-packaged for oral use. The high-profile names include US President Joe Biden and White House chief medical adviser Dr. Anthony S. Fauci -- both of whom after receiving negative testing results tested positive again in a "rebound" case.

In clinical trials, Paxlovid has shown to reduce the odds that a person at risk of severe Covid-19 would need to be hospitalised by almost 90 per cent compared with a placebo.

Meanwhile, the CDC has issued new guidance last week for people experiencing Covid-19 rebound after Paxlovid.

The CDC said people, who test positive again and whose symptoms come back after finishing their antiviral pills, should restart their isolation period and isolate for five full days.

The agency said people can end their isolation period after those five additional days as long as their fever has gone for 24 hours without fever-reducing medication and they're feeling better. The agency also recommends that people wear a mask for 10 days after their symptoms come back.