What is a breakthrough infection?
Quick Answer
A breakthrough infection is when a vaccinated person still gets infected with the disease the vaccine is meant to prevent. Vaccines can still greatly reduce severe illness even if they do not block every infection.
The Full Story
Breakthrough infections happen because no vaccine is perfect and because immunity can be less complete over time or against new variants. They are especially discussed for rapidly changing viruses such as influenza and SARS-CoV-2. Even when infection occurs, vaccination often lowers the chance of hospitalization, severe complications, and death. This is why vaccine success is usually measured by more than just whether infection occurs at all. Breakthrough infection does not mean a vaccine failed; it often means it worked partially, exactly as expected.
Key Facts
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