The Omicron variant of Covid is highly contagious but is known to cause less severe disease than Delta. This is after being better at escaping immune protection by vaccinations and previous infections. However, the reasons for this have so far remained elusive.
Now, a new study has shown that Omicron variant viruses are particularly sensitive to inhibition by the so-called interferon response, an unspecific immune response that is present in all body cells.
The study, led by researchers from the University of Kent and the Goethe-University Frankfurt, provides the first explanation of why Covid-19 patients infected with the Omicron variant are less likely to experience severe disease.
"This is due to Omicron, in contrast to Delta, does not effectively inhibit the host cell interferon immune response," said Prof Martin Michaelis, School of Bioscience, University of Kent.
The Omicron variant, first detected in late November, has swiftly spread to 171 countries so far. It has also outrun Delta variant to become the dominant strain in many countries. However, studies have shown it to cause only mild disease with less risk of hospitalisation and death.
The cell culture study also showed that Omicron viruses remain sensitive to eight of the most important antiviral drugs and drug candidates for the treatment of Covid-19.
This included EIDD-1931 (active metabolite of molnupiravir), ribavirin, remdesivir, favipravir, PF-07321332 (nirmatrelvir, active ingredient of paxlovid), nafamostat, camostat, and aprotinin.
"Although cell culture experiments do not exactly reflect the more complex situation in a patient, our data provide encouraging evidence that the available antiviral Covid-19 drugs are also effective against Omicron," said Prof. Jindrich Cinatl, Institute of Medical Virology at the Goethe-University.