What is a COVID-19 vaccine ‘breakthrough’ case?

A COVID-19 vaccine “breakthrough” case is when a vaccinated person gets infected with the coronavirus. Although the vaccines are very good at protecting people from severe illness, it’s still possible to get infected with mild or no symptoms, or even to get very sick. Experts say the shots are good at reducing the severity of any illness you might experience. But with the more contagious delta variant, health officials cite new data indicating vaccinated people who get infected could carry enough of the virus to spread it to others. Previously, officials believed vaccinated people were unlikely to spread the virus if infected.