The antiviral molnupiravir appears to remain effective against the Omicron variant of the SARS-CoV-2 virus, according to preliminary data, but monoclonal antibody treatments fare less well.
The in vitro data, published in the New England Journal of Medicine on 26 January 2022, appear to show molnupiravir and two other antivirals were just as effective against the Omicron variant as they were against earlier viral strains.
Molnupiravir (MK-4482, EIDD-2801; MSD and Ridgeback Therapeutics) is licensed for use in the UK in at-risk populations, such as those with diabetes or heart disease. In its first month of use, up to 16 January 2022, 5,426 packs of molnupiravir were dispensed in England.
The researchers carried out the laboratory study to measure the neutralising capacity of molnupiravir, remdesivir and an experimental drug called PF-07304814. They did not include nirmatrelvir (Paxlovid; Pfizer) — the other antiviral approved for use in patients with COVID-19 — in their study.
“The susceptibilities of Omicron to the three compounds were similar to those of the early strain (i.e., IC50 values for remdesivir, molnupiravir, and PF-07304814 that differed by factors of 1.2, 0.8, and 0.7, respectively),” the research paper concluded.
“These results suggest that all three of these compounds may show efficacy for treating patients infected with the Omicron variant.”
The researchers also looked at the ability of several monoclonal antibody treatments to neutralise the Omicron variant and discovered that sotrovimab, licensed on 17 December 2021 and widely used in the UK, retained some ability to neutralise the virus, although higher doses were needed compared with tests on alpha and delta strains of the SARS-CoV-2 virus .
The monoclonal antibodies casirivimab and imdevimab — which together form combined medicine Ronapreve (Roche and Regeneron) — also lost activity against the latest variant at commonly used doses.
The study findings, which still need to be replicated in human studies, corroborate other research suggesting monoclonal antibody treatments are proving less effective against the Omicron strain.
For this reason, in the UK, Ronapreve is no longer recommended against Omicron.
Study leader Yoshihiro Kawaoka, a virologist at the University of Wisconsin–Madison, said: “The bottom line is we have countermeasures to treat Omicron. That’s good news.
“However, this is all in laboratory studies. Whether this translates into humans, we don’t know yet.”