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    Fourth dose of COVID vaccine offers only slight boost against Omicron infection

    A fourth dose of a COVID-19 vaccine restores antibodies to levels observed after the third dose but provides only a modest boost in protection against infection, according to a small trial carried out in Israel1.

    The study, posted on the medRxiv preprint server on 15 February without peer review, suggests that current mRNA vaccines hit a “ceiling of immunity” after the third dose, says Miles Davenport, a computational immunologist at the University of New South Wales in Sydney, Australia. Further doses will probably only recover the immunity lost over time owing to waning, he says.

    “The third dose is really, really important,” says Gili Regev-Yochay, a physician and infectious-diseases researcher at Sheba Medical Center in Ramat Gan, who co-authored the study. But “people who are young and healthy and don’t have risk factors will probably not benefit much from a fourth dose” when faced with Omicron, she says.