[Bottles of Merck & Co.'s molnupiravir COVID-19 oral drug. (Photo by=BLOOMBERG)]

TOKYO: Researchers at Japanese and U.S. institutes revealed that some antibody medicines including Ronapreve may not be effective against the highly-mutated Omicron variant of the coronavirus,Kyodo reported.

The findings by Yoshihiro Kawaoka, a professor of virology at the University of Tokyo's Institute of Medical Science, and others were published in the New England Journal of Medicine on Wednesday. The researchers examined the neutralizing ability of approved and investigational therapeutic antibodies against Omicron and other variants of concern. The outcomes of their study, in which medicines were given to cultured cells of people exposed to the virus, showed that a Ronapreve antibody cocktail retained activity against Beta and Gamma variants but lost inhibitory capability against Omicron.

For now, the results suggested the oral drug molnupiravir and the IV drug remdesivir are likely effective against the highly-contagious variant. Sotrovimab, a monoclonal antibody drug, exhibited some efficacy against Omicron but it was lower compared with other variants including Delta. The Japanese Ministry of Health, Labor and Welfare decided in December not to recommend the administration of Ronapreve on patients who are potentially infected with the Omicron variant. Kawaoka and others said the potential limitations of their study include the lack of clinical data, and additional studies are necessary to determine whether these antiviral therapies are indeed effective or ineffective against infection with the Omicron variant.