COVID-19 Vaccine Breakthrough Cases: Data from the States – Kaiser Family Foundation

While COVID-19 vaccines are highly effective at preventing severe disease, hospitalization, and death from COVID-19 and also reduce the likelihood of mild or asymptomatic infection, a small share of fully vaccinated individuals do become infected, and some become hospitalized or have died. These rare occurrences are known as breakthrough cases which are to be expected, and historically known to occur with other vaccines as none is 100% effective.

The Centers for Disease Control and Prevention (CDC) currently monitors hospitalizations and deaths, from any cause, among fully vaccinated individuals with COVID-19, but not breakthrough infections, which it stopped monitoring as of May 1. CDC presents this data in aggregate at the national level but not by state, and there is no single, public repository for data by state or data on breakthrough infections, since the CDC stopped monitoring them.

We therefore reviewed the websites and other official state sources for all 50 states and D.C. to see which are providing data on COVID-19 breakthrough cases, hospitalizations and deaths, how regularly, and what those data may tell us. We only used data from official state sources (we did not include data available only in news media reports, for example). Where a state did not provide comparable data on overall COVID-19 cases, hospitalizations, or deaths reported over the period in which it captured breakthrough events, we obtained data on cases and deaths from the Johns Hopkins University COVID-19 Dashboard and on hospitalizations from the U.S. Department of Health & Human Services for the appropriate period (see methods for more detail).

Importantly, not all hospitalizations and deaths of those fully vaccinated and diagnosed with COVID-19 are due to COVID-19 or have a known cause at the time of reporting. The CDC reports that as of July 19, of 5,601 hospitalized breakthrough cases, 27% were asymptomatic or not related to COVID-19 and of 1,141 fatal cases, 26% were asymptomatic or not related to COVID-19. States differ in whether they provide this detail. DC, for example, reports that as of July 11, 50% of hospitalized breakthrough cases were due to COVID-19, 19% were not, and 31% were of unknown reason. However, few states made these distinctions. Where they did, we only included breakthrough hospitalizations and deaths due to COVID-19. In other cases, some of these breakthrough events may be due to causes other than COVID-19.

Overall, we find that:

While information on breakthrough events is still limited and incomplete, this analysis of available state-level data indicates that COVID-19 breakthrough cases, and especially hospitalizations and deaths, among those who are fully vaccinated are rare occurrences in the United States. Moreover, this data indicate the vast majority of reported COVID-19 cases, hospitalizations, and deaths in U.S. are among those who are unvaccinated or not fully vaccinated. These findings echo the abundance of data demonstrating the effectiveness of currently authorized COVID-19 vaccines. Moving forward, particularly as the more transmissible Delta variant is now the dominant strain of COVID-19 circulating in the U.S., more robust state-level data will help to monitor ongoing vaccine effectiveness and inform discussions about booster vaccinations.

We utilize two approaches in our analysis. The first assesses the share of fully vaccinated individuals that have experienced a COVID-19 event (i.e. diagnosis, hospitalization, or death) within each state. The second assesses the share of total COVID-19 cases, hospitalizations, and deaths attributable to fully vaccinated individuals compared to individuals who are not fully vaccinated within each state. Individuals who are not fully vaccinated may include those who are not vaccinated, partially vaccinated, or have an unknown vaccination status. In some cases, it is not possible to determine whether a hospitalization or death of a vaccinated individual with COVID-19 was due to COVID-19.

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COVID-19 Vaccine Breakthrough Cases: Data from the States - Kaiser Family Foundation