Why Vaccinated People Are Getting ‘Breakthrough’ Infections

The vaccines are effective, but they are not a golden shield against the coronavirus, particularly not the Delta variant.

A wedding in Oklahoma that led to 15 vaccinated guests becoming infected with the coronavirus. Raucous Fourth of July celebrations that dispersed the virus from Provincetown, Mass., to dozens of places across the country. As the Delta variant surges across the nation, reports of so-called breakthrough infections in vaccinated people have become increasingly frequent — including, most recently, when at least six Texas Democrats and an aide to Speaker Nancy Pelosi tested positive. The highly contagious variant, combined with the near absence of preventive restrictions, is fueling a rapid rise in cases in all states, and hospitalizations in nearly all of them. It now accounts for about 83 percent of infections diagnosed in the United States.