Merck plans to submit data on the antiviral medication to the US Food and Drug Administration (FDA) in the next few days. If they deliver a favourable decision within the next few weeks, the pill could be distributed soon afterwards.

If cleared, it would be the first pill shown to treat COVID-19.

All other therapies now authorised in the US require an IV or injection. A pill taken at home, by contrast, would ease pressure on hospitals and could also help curb outbreaks in poorer and more remote corners of the world that don't have access to the more expensive infusion therapies.

"This would allow us to treat many more people much more quickly and, we trust, much less expensively," said Dr William Schaffner, an infectious disease expert at Vanderbilt University who was not involved in the research.

Merck and its partner Ridgeback Biotherapeutics said early results showed patients who received the drug, molnupiravir, within five days of COVID-19 symptoms had about half the rate of hospitalisation and death as those who received a dummy pill.

The study tracked 775 adults with mild-to-moderate COVID-19 who were considered high risk for severe disease because of health problems such as obesity, diabetes or heart disease. The results have not been reviewed by outside experts, the usual procedure for vetting new medical research.

Among patients taking molnupiravir, 7.3 per cent were either hospitalised or died at the end of 30 days, compared with 14.1 per cent of those getting the dummy pill. After that time period, there were no deaths among those who received the drug, compared with eight in the placebo group, according to Merck.

The results were so strong that an independent group of medical experts monitoring the trial recommended stopping it early.

Dr Anthony Fauci, the government's foremost authority on infectious diseases, called the results from Merck "very good news."

But even with the news of a potentially effective new treatment, experts stressed the importance of vaccines for controlling the pandemic, given that they help prevent transmission and also reduce the severity of illness in those who do get infected.

White House coronavirus coordinator Jeff Zients said that vaccination will remain the government's main strategy for controlling the pandemic. "We want to prevent infections, not just wait to treat them when they happen," he said.

The US government has committed to purchasing enough pills to treat 1.7 million people, assuming the FDA authorises the drug.

Merck said it can produce pills for 10 million patients by the end of the year and has contracts with governments worldwide. The company has not announced prices.

Australian Associated Press