Pharmaceutical company Merck said Friday it will seek authorization in the US of its oral drug Molnupiravir for COVID-19 after it was shown to reduce the chance newly infected patients were hospitalized by 50 percent.

A simple pill to treat the coronavirus has been sought since the start of the pandemic and Friday's announcement was hailed as a major step towards that goal.

"With these compelling results, we are optimistic that molnupiravir can become an important medicine as part of the global effort to fight the pandemic," said Robert Davis, the company's CEO and president, in a statement.

Peter Horby, a professor of emerging infectious diseases at the University of Oxford, called the interim results "very encouraging."

He added: "A safe, affordable, and effective oral antiviral would be a huge advance in the fight against COVID-19."

But experts also cautioned they would like to see the complete underlying data, and stressed that if eventually approved the drug should complement highly effective vaccines, rather than be taken instead of them. 

Compelling results

In a late stage clinical trial, Merck and its partner Ridgeback Therapeutics evaluated data from 775 patients -- roughly half of whom received either a five-day course of the pill, while the other received a placebo.

All the patients had lab-confirmed COVID-19 with symptoms that developed within five days of them being assigned to their respective groups.

Of the patients who received molnupiravir, 7.3 percent were hospitalized by day 29, compared to 14.1 percent of those on a placebo -- a relative risk reduction of around 50 percent. 

There were also eight deaths in the placebo group but, significantly, none in the drug group.

Efficacy was said to hold up against variants of concern, including Delta, and the drug had a good safety profile.

The results were compelling enough that an independent data monitoring committee in consultation with the FDA decided to halt the trial early, which could indicate they felt it would be unethical to continue with a placebo arm.

Merck said it plans to submit an application for an Emergency Use Authorization (EUA) to the FDA as soon as possible based on these findings and plans to submit marketing applications to other regulatory bodies worldwide.

Response from the medical community was favorable, with some notes of caution.

"This is no substitute for vaccination. It's not a miracle cure but a companion tool," tweeted Peter Hotez, dean of Texas Children's Hospital.

Hotez also cautioned that if the drug is used carelessly, the public may end up developing resistance to the drug.

"If this is used indiscriminately, this can be a problem with antiviral drugs."

Experts also said it would be crucial to administer the drug early. Since it isn't always clear who is at risk for developing severe disease, it would have the greatest impact if it is cheap enough to distribute widely.

Broad application

Molnupiravir belongs to a class of antiviral drugs called "polymerase inhibitors," which work by targeting an enzyme that viruses need to copy their genetic material, and introducing mutations that leave them unable to replicate.

Such drugs are expected to be more variant-proof than monoclonal antibody treatments, which target a surface protein of the virus that is continually evolving.

It was initially developed as an inhibitor of influenza and respiratory syncytial virus, two other important acute respiratory infections, by a team at Emory University.

"If it is proven to be very safe and proven to be effective, then it can be used broadly, irrespective of the diagnosis, to treat and prevent multiple respiratory infections," Daria Hazuda, Merck's chief scientific officer of the company's exploratory science center, told AFP in a recent interview.