CDC identifies only 10,000 COVID-19 infections in fully vaccinated, but likely an undercount

More than 10,000 fully vaccinated people in the U.S. have experienced a “breakthrough” COVID-19 infection, according to a new Centers for Disease Control and Prevention (CDC) study.

According to the CDC, a total of 10,262 vaccine breakthrough infections had been reported from 46 U.S. states and territories as of April 30, out of the approximately 101 million people who were fully vaccinated against COVID-19 at the time.

The agency noted, however, that the breakthrough number in the report is likely a substantial undercount.

State health departments voluntarily report vaccine breakthrough infections to the CDC, and people voluntarily report infections to states, so the data might not be complete or representative.

Many people with vaccine breakthrough infections, especially those who are asymptomatic or who experience mild illness, might not seek testing, CDC said.

Going forward, the CDC is limiting the monitoring of people who have been infected while vaccinated. The agency is only sequencing a limited number of the cases, which has drawn concern from scientists. CDC said only 5 percent of breakthrough cases were sequenced.

In addition, beginning May 1 the CDC shifted from monitoring all reported breakthroughs to only those that result in hospitalization or death. The agency said the narrowed focus means only the cases of “highest clinical and public health significance” get reported.

Why it matters: Tracking and sequencing help identify who might be more at risk, and whether certain variants can escape the vaccine’s neutralizing effects. Scientists have questioned the benefit of limiting surveillance, when casting a wider net would likely be more beneficial.