A drug used to treat COVID-19 could be linked to mutations in the virus, scientists have said.
Molnupiravir works by causing mutations in the virus's genetic information, or genome, many of which kill or harm the virus, reducing the amount of COVID in the body.
Used across the world to treat COVID, it was one of the first antivirals available to doctors during the pandemic.
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But researchers who mapped virus mutations across global databases, have found that some COVID mutations linked to patients taking molnupiravir were very different to the usual mutations they saw, meaning it could lead to further infection.
Christopher Ruis, from the Department of Medicine at the University of Cambridge, said molnupiravir "belongs to a class of drugs that can cause the virus to mutate so much that it is fatally weakened".
"But what we've found is that in some patients this process doesn't kill all the viruses, and some mutated viruses can spread," he said.
"This is important to take into account when assessing the overall benefits and risks of molnupiravir and similar drugs."
The study, by researchers at the Francis Crick Institute, the University of Cambridge, Imperial College London, the University of Liverpool, the University of Cape Town and the UK Health Security Agency (UKHSA), also found the mutations were more likely in older age groups consistent with the use of the antivirals to treat people who are more at risk.
Almost a third (30%) of the events in England involved the use of molnupiravir, treatment data showed.
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Theo Sanderson, lead author and postdoctoral researcher at the Francis Crick Institute, said: "Our evidence shows that a specific antiviral drug, molnupiravir, also results in new mutations increasing the genetic diversity in the surviving viral population.
"The possibility of persistent antiviral-induced mutations needs to be taken into account for the development of new drugs which work in a similar way."
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