Britain banks on antivirals molnupiravir and paxlovid to tackle Omicron this winter

UK has bought 500,000 molnupiravir doses, but paxlovid is yet to be approved for use

Merck's molnupiravir, which decreases the ability of a virus to replicate. AFP

Britain expects to have antiviral Covid-19 pills produced by Merck and Pfizer available over the winter, its antiviral taskforce chairman said on Thursday, as Omicron continues its advance through the UK.

Eddie Gray said he expected Merck's molnupiravir and Pfizer's paxlovid treatments to be available throughout the winter period, which he defined as between now and the end of March. Britain has yet to approve paxlovid.

"If there's a successful approval of paxlovid we'll want to fold that into the panoramic process," Mr Gray said, referring to a UK clinical trial examining the effectiveness of antiviral treatments against Omicron in a highly vaccinated population.

Britain last month became the first country to approve molnupiravir, jointly developed with Ridgeback Biotherapeutics. Merck says it has signed deals totalling more than 7 million courses.

Panoramic is under way, testing Merck's pill in Covid-19 patients at risk of serious illness, hoping to reduce strain on hospitals.

It has enlisted more than 250 people out of a target of 10,000 subjects, Mr Gray said.

"Early treatment in the community could have the furthest reach and impact here," chief investigator Prof Chris Butler said.

"Diminishing the burden on hospitals and getting people recovering quicker is the next phase in this area of research."

But recent data from separate trials showed the drug only reduced the number of people needing hospital treatment and deaths among high-risk patients by about 30 per cent, compared with 89 per cent for paxlovid.

Britain has bought 500,000 molnupiravir doses.

Prof Butler said Panoramic was testing molnupiravir first because its data became available before information for paxlovid

"It's not yet approved and not yet available," he said. "Evidence emerging for paxlovid has been subsequent to monulpiravir, hence the lag between the two.

"It's a question of getting on with what's available."

The hope is that Panoramic will shed light on which Covid-19 tablets reduce the need for people to seek hospital treatment, prevent severe cases, avoid immune resistance and prove cost-effective.

Whether such drugs could be used to protect people from becoming ill after being exposed to a positive case, known as post-exposure prophylaxis, is another possibility scientists and regulators are keen to explore.

"Antivirals will be a way of dealing with Covid-19 over the winter and in the long run, as well as answering questions like efficacy as a post-exposure prophylaxis," said Prof Phil Evans, of the National Institute of Health Research.

The molnupiravir treatment is still under review by the European Medicines Agency, but the EU drug regulator issued advice in November on using it for older adults ahead of providing any wider recommendation.

The EMA said on Thursday that EU countries can use paxlovid early after diagnosis of an infection, even though its full review for approval has not been completed.

Both paxlovid and molnupiravir work by impairing the coronavirus's replication, sparking hope that such a mechanism could prove effective against other mRNA viruses such as Sars and Mers, says Dr David Lowe of the National Health Service England.