Covid drug prescribed to more than 20,000 British patients may cause the virus to mutate, scientists warn

A Covid drug hailed as a game-changer and prescribed to over 20,000 British patients may actually cause the virus to mutate, scientists warned today.

Molnupiravir is given to thousands of vulnerable Brits who test positive, such as patients fighting cancer or liver and kidney disease.

The antiviral, made by US pharma giant Merck, protects against severe illness by forcing mutations in the virus that fatally weaken it.

However, in some cases these mutations do not kill off the virus, say researchers at the Francis Crick Institute and UK Health Security Agency (UKHSA).

Instead, a patient can remain infected with a mutated version of Covid and pass this on to others, according to the team’s analysis of millions of virus sequences.

Experts have warned it is now crucial to find out if mutations triggered by molnupiravir make the virus more transmissible or severe, or allow it to bypass immunity from previous infections or vaccines.

Some have even warned that its use could lead to new variants spawning, although the manufacturer has rubbished such fears.

Molnupiravir, sold under the brand name Lagevrio, works by stopping Covid from growing and spreading in an infected person, keeping virus levels low.

This helps the body’s immune system control the infection, reducing the risk of severe symptoms and hospitalisation.

Clinical trials suggest the drug — which was rolled out to patients in the UK from December 2021 and described as an ‘excellent addition’ to the country’s ‘armoury against Covid’ — halves the risk of being admitted or dying from Covid.

The team, which included scientists from the University of Cambridge, Imperial College London, the University of Liverpool and the University of Cape Town, noted molnupiravir’s effects are a result of it triggering an array of mutations in the virus.

Many of the mutations damage or kill the virus.

However, in some patients, the virus is not fully cleared, meaning they can infect others with the molnupiravir-mutated virus.

They examined a family tree of 15million Covid sequences, collected from global databases, to map its mutations over time.

Covid mutates constantly and most have little to no impact on the virus’s properties, such as how transmissible it is or the severity of infection that it triggers.

However, in a study published in the journal Nature, the researchers said they spotted changes to the virus that looked very different to the expected patterns.

These mutations were strongly linked with people who had taken molnupiravir.

The team noted that the frequency of these mutations increased in 2022, which is when the rollout gathered pace.

The unusual changes to the virus were also more common among older people — who are more likely to be given the drug — in countries known to have high molnupiravir use and among samples taken during clinical trials of the drug.

Three in 10 of the abnormal mutations seen in England were among those given the drug, according to the researchers.