Merck’s COVID pill loses its lustre

Molnupiravir was initially heralded by public-health officials as a game-changer for COVID-19, but full clinical-trial data showed lower-than-expected efficacy.

An FDA advisory committee met on 30 November, and narrowly voted to recommend the drug candidate’s emergency approval by 13 to 10.

The agency’s lengthy deliberations could signal uncertainties about the antiviral’s efficacy and safety: full trial data submitted to the FDA suggest that molnupiravir is less effective than originally thought, dampening scientists’ hopes that the relatively cheap and easy-to-administer treatment might change the course of the pandemic.

decreased the risk of hospitalization from COVID-19 by 30% — down from a 50% reduction observed early in the trial.

Monoclonal antibody treatments, by contrast, reduce the risk of severe COVID-19 by up to 85%. But they are costly and need to be administered intravenously, so finding an effective oral antiviral for the disease has been a high priority for scientists around the world who want to be better able to treat high-risk patients in rural areas and under-resourced countries, Seley-Radtke says.

Nicholas Kartsonis, the senior vice-president of clinical research at Merck, told the FDA advisory committee on 30 November that the company couldn’t explain the starkly different results, which have not been peer reviewed. Some of the committee members pointed out that the highly transmissible Delta variant of the SARS-CoV-2 coronavirus had not yet become dominant globally during the first half of the trial, whereas it had by the second half. This might mean that molnupiravir isn’t as effective against Delta as it is against some other variants.

some researchers are worried that molnupiravir’s novel mechanism of action has the potential for long-term safety risks. The antiviral works by incorporating itself into the virus’s RNA, creating errors and hamstringing SARS-CoV-2’s ability to replicate.

Intentionally introducing mutations into viral RNA might create a more dangerous version of SARS-CoV-2, critics say.

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