Delta variant breakthrough cases by state: Here’s what the latest research says

“Breakthrough cases”—those in which a fully vaccinated person tests positive for COVID-19’s delta variant—are very rare. But they do happen, as no vaccine is 100% effective. However, the infection rates among unvaccinated people are continuing to rise, especially in states where a majority of residents haven’t gotten the shot yet.

Although there is no single definitive repository for state-by-state data (the Centers for Disease Control and Prevention has stopped monitoring), the Kaiser Family Foundation (KFF) reviewed data from official websites and state sources for all 50 states and D.C. to see which are showing more COVID-19 breakthrough cases, hospitalizations, and deaths. This data varies, as each state reports this information differently and less than half are even reporting data on breakthrough cases. If the state didn’t have a report, KFF looked to Johns Hopkins University and the U.S. Department of Health and Human Services for hospitalization totals.

Among the notable findings from KFF’s report:

The rate of breakthrough cases reported among those fully vaccinated is well below 1% in all reporting states, ranging from 0.01% in Connecticut to 0.29% in Alaska.
The rates of death among fully vaccinated people with COVID-19 were even lower, effectively zero (0.00%) in all but two reporting states, Arkansas and Michigan, where they were 0.01%. (Note: Deaths may or may not have been due to COVID-19.)
More than 9 in 10 COVID-19 cases, hospitalizations, and deaths have occurred among people who are unvaccinated or not yet fully vaccinated, in those states reporting breakthrough data.

“This data indicate the vast majority of reported COVID-19 cases, hospitalizations, and deaths in the U.S. are among those who are unvaccinated or not fully vaccinated,” the authors write. “These findings echo the abundance of data demonstrating the effectiveness of currently authorized COVID-19 vaccines.”