A WHO expert explains why she believes the rush for Covid-19 boosters is premature

When the World Health Organization last week called for a moratorium on giving Covid-19 booster shots, except in rare circumstances, it said it was concerned wealthy countries would start giving their populations a third dose before the people at highest risk from the disease — health workers and older adults — in many countries get their first. But Kate O’Brien, the WHO’s director of immunization, vaccination, and biologics, recently insisted on an additional reason: Providing booster shots without strong evidence that the shots are needed is ill-advised. “If we’re not really grounded in that clarity, we’re going to be in a place where we have forever uncertainty about what actually should be done,” she cautioned.