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About 27% of people who get COVID-19 have a rebound of their symptoms, regardless of whether they took the antiviral treatment Paxlovid, according to a new preprint study published on medRxiv that hasn’t yet been peer-reviewed.
Symptoms can return after the person’s condition improves, and the symptoms can be better or worse than the original bout of illness, the study authors said.
“It happens all the time. People who are untreated with COVID who then feel better can get symptoms afterward,” Davey Smith, MD, one of the study authors and chief of infectious diseases and global public health at the University of California, San Diego School of Medicine, told NBC News.
“Symptoms fluctuate, and viral antigen in the nose fluctuates, and they fluctuate with and without Paxlovid,” he said.
Smith and colleagues looked at viral and symptom rebound in 568 untreated patients with mild to moderate COVID-19 who received a placebo in a clinical trial for one of Eli Lilly’s monoclonal antibody treatments. The researchers collected nasal swabs on days 0 to14, 21, and 28, and the people in the study recorded how severe their symptoms were from days 0 to 28.
Overall, symptom rebound occurred in 27% of people after their symptoms improved at first, and in 10% of people after their symptoms first got better.
What’s more, about 12% of people had a “viral rebound,” which means they tested positive again after several days of testing negative. This has been documented among people who have taken Paxlovid, including President Joe Biden, but the study found that viral rebound can occur regardless of treatment.
At the same time, the combination — high-level viral rebound and symptom rebound after improvement — was relatively rare, occurring in about 1% to 2% of people.
But symptom rebound isn’t unique to COVID-19, one expert said.
“It some ways, that’s the natural history of all respiratory viral infections,” Paul Sax, MD, clinical director of the Infectious Diseases Division at Brigham and Women’s Hospital in Boston, told the news outlet.
“There are good days and bad days, and then they eventually get better,” he said.