How the use of this anti-COVID drug may have led to mutations in the virus

Molnupiravir was one of the earliest treatments rolled out during the pandemic, and works mainly by creating mutations in the virus with the goal of weakening and killing it.

The drug, which is taken orally over a five-day course, works mainly by creating mutations in the virus with the goal of weakening and killing it. Source: AAP / Daniel Bockwoldt/DPA

Key Points

• A study from the UK shows that a popular anti-COVID drug may have led to mutations of the COVID-19 virus.
• The manufacturer of molnupiravir, pharmaceutical giant Merck, has refuted the findings.
• Several experts claim the study is "incredibly important".

An anti-COVID drug widely used across the world may have caused mutations in the virus, researchers said on Monday, but there was no evidence that the changes had led to more dangerous variants.

Pharmaceutical giant Merck's antiviral pill molnupiravir was one of the earliest treatments rolled out during the pandemic to prevent COVID-19 from becoming more severe in vulnerable people.

The drug, which is taken orally over a five-day course, works mainly by creating mutations in the virus with the goal of weakening and killing it.

However, a new UK-led study has shown that molnupiravir "can give rise to significantly mutated viruses which remain viable," lead author Theo Sanderson told AFP.

Sanderson, a geneticist at London's Francis Crick Institute, emphasised that there is no evidence that "molnupiravir has to date created more transmissible or more virulent viruses".

None of the variants that have swept the world were due to the drug, he added. But "it is very difficult to predict whether molnupiravir treatment could potentially lead to a new widely circulating variant which people don't have prior immunity to," he added.

Researchers found signs of a "mutational signature"

For the study, which was published in the journal Nature, the researchers sifted through databases of more than 15 million genome sequences of SARS-CoV-2, the virus that causes the COVID disease.

The researchers used this data to track changes in how the virus mutated during the pandemic, finding signs of a particular "mutational signature" in patients they believe are linked to molnupiravir.

The antiviral medication molnupiravir was specially approved as a medicine for internal use of COVID-19. Source: AP / Daisuke Urakami

In 2022, as the drug was prescribed in huge numbers, there was a significant increase in patients who had this mutational signature, the study found.

This signature was more commonly found in countries where the drug was widely prescribed, such as the United States, United Kingdom, Australia and Japan. But in countries where it was not approved, including Canada and France, it was rarer.

Merck attempts to shut down links between drug and COVID mutation

Merck refuted the study, saying the researchers had relied on "circumstantial associations" between where and when the sequences were taken.

"The authors assume these mutations were associated with viral spread from molnupiravir-treated patients without documented evidence of that transmission," Merck said in a statement sent to AFP.

Sanderson rebuffed this claim, saying the researchers had used "several independent lines of evidence to identify with confidence that molnupiravir drives this mutational signature".

That included a separate analysis of treatment data in England, which found that more than 30 per cent of mutation events involving the signature were in people who had taken molnupiravir.

However, just 0.04 per cent of people in England were prescribed the drug in 2022, the study said.

Other anti-COVID drugs do not work in the same manner, so would not cause these kinds of mutations, Sanderson said.

Experts not involved in the study seemed to side with the British researchers. Stephen Griffin, a virologist at the UK's University of Leeds, said it was an "incredibly important, well-conducted piece of research".