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Antibody drugs' efficacy lower for omicron compared with delta: Japan study

This electron microscope photo shows the coronavirus's omicron variant successfully isolated at the National Institute of Infectious Diseases. (Photo courtesy of the National Institute of Infectious Diseases.)

TOKYO -- Antibody drugs that help prevent a virus sticking to cells may be less effective for the coronavirus's omicron variant than for the delta strain, a study by a team from the University of Tokyo's Institute of Medical Science and the National Institute of Infectious Diseases has found.

    At the same time, the researchers found that antiviral medications that prevent viral reproduction inside the body showed about the same efficacy for the two variants. Their findings were published online in the Jan. 26 edition of the New England Journal of Medicine.

    The team led by Yoshihiro Kawaoka, a project professor of virology at the University of Tokyo, used cultured cells to test the efficacy of existing drugs to treat COVID-19. Antibody medication blocks the virus from sticking to cells and helps prevent viral reproduction, and in Japan, antibody cocktail Ronapreve and neutralizing antibody sotrovimab (brand name Xevudy) have been approved for use.

    The result showed that Ronapreve's efficacy in preventing omicron from reproducing was 1/5,261 or less compared to its effectiveness against the delta variant. Sotrovimab was about two-thirds less effective against omicron than delta.

    Antiviral medications, meanwhile, obstruct the function of an enzyme the virus needs to multiply once it enters the body. Oral medication molnupiravir is one such drug recently approved in Japan.

    In the experiment, molnupiravir and IV-administered remdesivir (also approved in Japan) reportedly prevented reproduction of delta and omicron about equally.

    As omicron is rapidly spreading around the globe, a selection of effective medication is essential to ease the strain on medical care providers. Kawaoka told the Mainichi Shimbun, "As far as antibody drugs go, we believe it's become difficult for the antibody agent to bind with the spike protein on the surface of the virus due to the omicron variant's multiple mutations. It's necessary to carefully determine efficacy in clinical settings."

    (Japanese original by Ayumu Iwasaki, Science and Environment News Department)

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