AdvertisementVaccine Refusal May Put Herd Immunity At Risk, Researchers Warn04:32Download AudioResumeApril 07, 2021Geoff BrumfielfacebookEmailNearly a third of adults in the U.S. have gotten at least one shot of the COVID-19 vaccine so far, but researchers warn that vaccine refusal may keep the country from reaching herd immunity. (The Boston Globe via Getty Images)