People vaccinated against COVID-19 may be sick…See more

After vaccination, the immune system learns to recognize specific parts of the virus. This preparation allows the body to respond faster if infection occurs. However, viruses can still enter the body and begin replicating before the immune response fully activates.

For this reason, breakthrough infections can happen even among fully vaccinated individuals.

Health authorities around the world have repeatedly noted that COVID-19 vaccines remain highly effective at preventing severe disease, but they cannot guarantee that every vaccinated person will avoid infection entirely.

Why Breakthrough Infections Happen

Several factors contribute to COVID-19 infections among vaccinated people.

1. Viruses Change Over Time

Like many viruses, SARS-CoV-2 continuously evolves through mutations. New variants may partially evade immune defenses developed through previous vaccination or infection.

While vaccines often continue to provide strong protection against severe outcomes, their effectiveness against infection itself may decrease as new variants emerge.