New York, July 31 Treatment of Covid with Pfizer's antiviral drug Paxlovid, which has shown to cause a rebound of infection, can also be contagious, even without any symptoms, according to a study that has not been peer-reviewed yet.
US President Joe Biden, who first tested positive for Covid-19 on July 21, before receiving his negative testing results, earlier this week, has tested positive again in a "rebound" case, White House physician Kevin O'Connor wrote in a memo on Saturday.
Biden, 79, is fully vaccinated and twice boosted, and also took Paxlovid.
O'Connor wrote that the President "has experienced no reemergence of symptoms, and continues to feel quite well" but will reinitiate strict isolation procedures.
A similar case happened when White House chief medical adviser Anthony S. Fauci tested positive last month.
The study, posted on pre-print website, described relapse of Covid symptoms and SARS-CoV-2 viral load following Paxlovid pill (consisting of nirmatrelvir and ritonavir tablets, co-packaged for oral use) in 10 non-immunocompromised patients aged between 31 to 71 years.
Most patients improved rapidly after treatment with Paxlovid and had negative antigen or PCR tests prior to relapse on days 9-12 of their illness.
Relapse symptoms were described most frequently as cold symptoms, though some patients experienced a recurrence of fatigue and headache. All relapses resolved without additional antiviral treatment.
Viral load during relapse was comparable to levels during initial infection. Sequencing in three patients indicated that relapse was not due to a treatment-emergent mutation or infection with a different viral strain.
One symptomatic and one presymptomatic patient transmitted SARS-CoV-2 to family members during relapse.
"The presence of high viral load and the occurrence of two transmission events suggest that patients with relapse should isolate until antigen testing is negative," the researchers wrote in the paper.
In clinical trials, Paxlovid has shown to reduce the odds that a person at risk of severe Covid would need to be hospitalised by almost 90 per cent compared with a placebo.
Meanwhile, the US Centres for Disease Control and Prevention has issued new guidance last week for people experiencing Covid rebound after Paxlovid, CNN reported.
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 was gone for 24 hours without fever-reducing medication and they're feeling better. The agency also recommended people to wear a mask for 10 days after their symptoms come back, the report said.
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