Using the antiviral drug molnupiranir does not decrease deaths or hospital admissions among COVID-19 patients who are vaccinated and at higher risk of mortality, according to a study published in The Lancet journal.

The trial with over 25,000 participants, however, suggests that patients taking molnupiravir recovered faster -- on average 4.2 days quicker -- compared to patients in the control group.

Previous studies suggested that molnupiravir is effective at reducing hospital admissions in patients with mild to moderate COVID-19 and WHO recommends its use for patients with the highest risk of hospital admission.

However, studies have so far been conducted in largely unvaccinated populations prior to the emergence of the Omicron variant.

The new study was carried out in a vaccinated population where most COVID-19 infections were the Omicron variant.

Molnupiravir is one of the more expensive antivirals used to treat COVID-19, with a seven-day course costing around USD 700 in the US.

Molnuvirapir was sent directly to the trial participants and was able to be taken orally at home.

"Although this trial found no benefit from molnupiravir treatment on its primary outcome -- which hypothesised that treatment with molnupiravir for vaccinated, at-risk patients would reduce the likelihood of hospitalisation or death -- the trial suggests that this treatment could have other benefits when being used to treat COVID-19, such as a faster recovery time and reduced follow up with health services," said lead author, Professor Chris Butler, from the University of Oxford, UK.

The study included 25,708 participants over the age of 18 (average age 57 years) with a higher risk of death or hospitalisation from COVID-19 infection from health centres across the UK.

Patients were considered at higher risk of hospitalisation or death if they were aged 50 years or older -- or aged 18 years or older with relevant underlying health conditions.

Patients had a confirmed Omicron COVID-19 infection and were unwell for five days or less before beginning treatment. The results represent outcomes for patients treated between December 8, 2021, and April 27, 2022, during the peak of the Omicron wave in the UK.

Approximately half the patients in the trial (12,774 people) received 800mg molnupiravir twice daily for five days, which was taken at home, in addition to standard care. The control half of the trial (12,934 people) received standard care only.

There was no benefit observed in hospitalisation or death rates between the molnupiravir group and the control group, the study found.

In the group treated with molnupiravir there were 105 cases of death or hospitalisation (0.8 per cent), while in the control group there were 98 cases of death or hospitalisation (0.8 per cent).

Participants receiving molnupiravir reported more favourable outcomes for a variety of secondary outcomes in this study.

The median average length of illness in patients who took molnupiravir was nine days, compared to 15 days in the control group.

Using statistical modelling that accounted for the range of recovery times across both groups, the researchers found that patients taking molnupiravir recovered an average of 4.2 days quicker compared to patients in the control group.

In addition, seven patients in the control group did not reach recovery within the 28 days of follow-up, the researchers added.