Lagevrio, the FDA-authorized oral COVID-19 therapy developed by Merck (NYSE:MRK) and Ridgeback Biotherapeutics, leads to new mutations in the virus with the potential for further spread, according to a new study based on millions of viral samples.

The researchers in the U.S. collaborated with those in the U.K.’s Francis Crick Institute, Imperial College, and the University of Liverpool to conduct the study, the results of which were published as a preprint last week ahead of peer review.

In December 2021, the FDA greenlighted, Lagevrio, also known as molnupiravir, for at-risk adults who test positive for COVID-19.

Citing an analysis of more than 13M viral genomes in global databases, the investigators noticed that Lagevrio-linked mutations were proportionally more common in countries and age groups where the drug is widely used, such as Australia, the U.S., and the U.K.

The researchers noted that countries like Canada and France, where Lagevrio is not authorized, indicated a low number of mutations.

According to investigators, Lagevrio-induced mutations were found in small patient groups indicating further spread of new versions.

Though the largest group with similar mutations comprised 21 individuals, it did not reflect the seriousness of the issue as the analysis didn’t represent viral samples of many, Ryan Hisner, a U.S.-based scientist who was part of the study, said.

“These effects are visible in these databases,” lead researcher Theo Sanderson, from Francis Crick Institute, told Bloomberg. “It appears that people are being treated, some of them aren’t clearing their infections, and some are passing them on.”

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