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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.

COVID-19 cases in vaccinated people have become increasingly common in recent months amid the spread of the delta variant and the waning of immunity from vaccination, according to new Yale research conducted in Connecticut.

Breakthrough SARS-CoV-2 infections tend to be mild, but new Yale research shows that more older adults have developed severe breakthrough cases during the Delta variant phase of the pandemic, particularly after a longer period of time had elapsed since their last vaccination.

A new study from Yale confirms what you suspected: COVID-19 breakthrough cases are on the rise, but delta is not the culprit this time.

For fully vaccinated Americans, the risk of being hospitalized or dying from Covid-19 is low — much lower than the risk for unvaccinated people. But in those rare cases when a fully vaccinated person gets infected, data suggests it's older adults and those with multiple underlying medical conditions who are most at risk of serious illness.

These patients tended to be older—between 65 and 95 with a median age of 80.5—and had preexisting comorbidities, such as cardiovascular disease and type 2 diabetes. A subset of patients was also on immunosuppressive drugs that may affect vaccine efficacy.

Dr. Hyung Chun speaks about COVID-19 “Long haulers.”

Three proteins found in the blood of post-COVID patients appear to predict who may have long-term symptoms of the disease.

Yale researchers have helped identify the mechanisms behind a major cause of morbidity and mortality in COVID-19 patients.