Breakthrough infection

A breakthrough infection is a case of illness in which a vaccinated individual becomes sick from the same illness that the vaccine is meant to prevent. Simply, they occur when vaccines fail to provide immunity against the pathogen they are designed to target.

7 Breakthrough COVID Cases Have Hit the New York Yankees

Seven people traveling with the New York Yankees, including three coaches, have tested positive for COVID-19—and all were fully vaccinated against the virus.
The team made the announcement about the breakthrough cases in a press conference on March 11, noting that four non-coach support staff members also tested positive for the virus. All seven of those who tested positive received the Johnson & Johnson vaccine, the team said, and just one of the seven had "some symptoms" of COVID-19. The positive cases were picked up through routine testing.