The Centers for Disease Control and Prevention (CDC) stopped tracking all breakthrough cases of COVID-19—those that occur in people vaccinated against the virus—in May 2021 and has since only tracked breakthrough cases that lead to hospitalization or death.
While the agency has published several studies in the past year as part of an effort to better understand the effectiveness of the COVID-19 vaccines, some critics say that not having a national tally of breakthrough cases is limiting that effort.
