Hyung Chun, M.D.; Image credit: Yale Medicine
Hyung Chun, M.D.; Image credit: Yale Medicine

The number of older adults developing severe breakthrough COVID-19 infections spiked after the delta variant became the dominant coronavirus strain, according to a new study conducted across a Connecticut hospital system.

This finding may not be a surprise to long-term care clinicians, many of whom have witnessed this trend first-hand in their facilities. But the study also showed that the more time elapsed since initial vaccination, the greater the odds of severe reinfection illness for these older patients.

This result highlights the need for timely booster vaccinations, particularly for older individuals and others who are highly vulnerable to developing severe breakthrough infections, wrote researcher Hyung Chun, M.D., of Yale, and colleagues.

Chun and his team examined health data from patients hospitalized in the Yale New Haven Health System between August and mid-October 2021, when the delta variant accounted for more than 95% of infections in that region. Among them, 371 tested positive for SARS-CoV-2, and 22% of these were severely or critically ill with breakthrough COVID-19 infections. 

This is a significant change when compared to a rate of 1.4% of severe breakthrough infections among older patients during March and July 2021, the researchers reported. In addition, the further out the patient was from the time of vaccination, the greater the likelihood of a poor outcome, they noted.

“This highlights the importance of booster doses, as the efficacy of the vaccines appears to wane over time,” Chun said in a statement. “Especially with the emergence of the omicron variant, we need to reconsider our definition of being fully vaccinated to include the booster vaccinations.”

The study was conducted before the rise of the omicron variant. 

Full findings were published in the Lancet.