Risk of severe Covid-19 breakthrough case higher among seniors and those with comorbidities

For Americans who are fully vaccinated against the novel coronavirus, the risk of hospitalization or death due to the virus is low, and significantly lower than the risk for those who are unvaccinated. Unvaccinated adults are 17 times more likely to be hospitalized for a Covid-19 infection than adults who are fully vaccinated, Centers for Disease Control and Prevention data shows.

However, breakthrough cases are possible, and in those cases, new data suggests that it is primarily older adults and individuals with multiple underlying medical conditions who are at highest risk of serious illness. 

Through August, the CDC has received reports of just under 13,000 severe breakthrough cases of Covid-19 in fully vaccinated people that resulted in either hospitalization or death. Of the more than 173 million Americans who were fully vaccinated by the end of last month, that represents about a 0.000075% chance of experiencing a severe breakthrough case. 

For the breakthrough cases that are occurring, about 70% of those that result in hospitalizations happened among adults aged 65 and up, as were 87% of those that resulted in death, according to the CDC data.

Among vaccinated adults with breakthrough virus cases that landed them in the hospital, more than 70% of the individuals had three or more underlying conditions. The same study found that among unvaccinated individuals hospitalized with coronavirus, just 56% had three or more underlying conditions.