From June to September 2021, fully vaccinated people with breakthrough COVID-19 accounted for 15 percent of all U.S. COVID-19 hospitalizations, according to data from Peterson's and Kaiser Family Foundation's Health System Tracker.
The data is from Cosmos, a HIPAA-defined dataset of more than 120 million patients from over 140 Epic organizations, including 250 hospitals across all 50 states and data on nearly 10 million admissions. More than 120,000 COVID-19 hospitalizations were examined.
Individuals were considered fully vaccinated if they had received the required dose(s) of a COVID-19 vaccine and were at least 14 days from the single-dose vaccine or the second dose in an mRNA series.
Six findings:
1. An overwhelming majority of COVID-19 hospitalizations were among unvaccinated or partially vaccinated people. From June to September 2021, 85 percent of virus hospitalizations were among those not fully vaccinated against COVID-19.
2. Age was highly correlated with breakthrough hospitalizations. The majority of COVID-19 breakthrough hospitalizations were of people 65 and older, while the majority of people not fully vaccinated and hospitalized with COVID-19 were adults ages 18 to 64. Only 10 percent of breakthrough hospitalizations were people under age 50.
3. Compared to the age distribution of fully vaccinated people in the U.S., people 65 and up make up a disproportionately large share of breakthrough hospitalizations. As of Sept. 30, 25 percent of fully vaccinated Americans were 65 and older. In comparison, in the Epic sample, 69 percent of fully vaccinated people hospitalized with breakthrough COVID-19 were 65 and older.
4. A greater share of people hospitalized with a breakthrough COVID-19 case also had at least one comorbidity compared to COVID-19 patients who weren't fully vaccinated.
5. Breakthrough hospitalizations included fewer COVID-related respiratory complications or treatments, suggesting fully vaccinated patients hospitalized with breakthrough COVID-19 may have been more likely to be hospitalized for unrelated reasons.
6. Fully vaccinated adults hospitalized with COVID-19 had shorter average hospital stays than those who weren't fully vaccinated within the same age group. Among patients over 65, the median COVID-19 hospital stay was 1.1 days shorter for those who were fully vaccinated (5.6 days) than for those not (6.7 days).