What is a COVID-19 vaccine 'breakthrough' case?

A small number of COVID-19 “breakthrough” cases are expected after vaccination, and health officials say they’re not a cause for alarm

What is a COVID-19 vaccine “breakthrough” case? It’s when a fully vaccinated person gets infected with the coronavirus. A small number of such cases are expected and health officials say they're not a cause for alarm. COVID-19 vaccines work by teaching the body to recognize the virus. So if you’re exposed to it after vaccination, your immune system should be ready to spring into action and fight it. In studies, the two-dose COVID-19 vaccines by Pfizer and Moderna were around 95% effective at preventing illness, while the one-shot Johnson & Johnson shot was 72% effective, though direct comparisons are difficult. So while the vaccines are very good at protecting us from the virus, it’s still possible to get infected with mild or no symptoms, or even to get sick.