As of April 30, when roughly 101 million Americans had been fully vaccinated against COVID-19, "breakthrough" infections had been reported in 0.01% of them, the U.S. Centers for Disease Control and Prevention (CDC) reported on Tuesday. Roughly 27% of breakthrough infections were asymptomatic, while in 2% of cases, patients died. The CDC had genetic data for virus samples from 555 breakthrough infections. Mutated variants of the coronavirus, including those first seen in the UK and South Africa, accounted for 64% of the breakthroughs. In a separate study posted Tuesday on medRxiv ahead of peer review, researchers reported that among 20 fully-vaccinated healthcare workers with breakthrough COVID-19 cases, all were infected with variants. An earlier study had linked breakthrough infections with low viral loads, suggesting low transmission risks, but "we found many samples in our breakthrough cohort with high viral load," said coauthor Pavitra Roychoudhury of the University of Washington. "Our work suggests that not all breakthrough infections are at low risk of initiating transmission and, if they did, these infections could lead to the continued spread of variants of concern, particularly in areas with low vaccination rates," Roychoudhury added. —Reuters Staff Source
