Amid persistent concerns that the protection offered by COVID-19 vaccines may be waning, a report released Friday by the Centers for Disease Control and Prevention finds that America's workhorse shot is significantly less effective at preventing severe cases of disease over the long term than many experts had realized. Data collected from 18 states between March and August suggest the Pfizer-BioNTech vaccine reduces the risk of being hospitalized with COVID-19 by 91% in the first four months after receiving the second dose. Beyond 120 days, however, that vaccine efficacy drops to 77%. Meanwhile, Moderna's vaccine was 93% effective at reducing...