Study finds low rate of COVID-19 "breakthrough" infections, fewer symptoms in vaccinated people

London — A study conducted in the U.K. offers some of the first large-scale, real-world data on how well vaccination protects people against catching a "breakthrough" COVID-19 infection, and how well it protects breakthrough patients from becoming seriously ill. The results are encouraging.

The peer-reviewed study published Wednesday in The Lancet medical journal will help policy makers and epidemiologists fill in a significant gap in the understanding of the true efficacy of three of the major vaccines being used worldwide. The U.S. Centers for Disease Control and Prevention, for instance, doesn't have good data on how many people catch COVID-19 after being vaccinated, as it decided in the spring to track only serious, symptomatic breakthrough cases. The British study, on the other hand, used mass-testing data to determine how many breakthrough cases there actually are and how sick those people get.