Covid-19 Vaccine - Immunity

Below are frequently asked questions related to COVID-19 vaccine immunity. Click on another category to the left to see more FAQs.

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Yes. When someone who is fully vaccinated tests positive for COVID-19, it is called a “breakthrough” case. Breakthrough cases are expected and relatively common. Oftentimes, vaccinated people who have a breakthrough infection are asymptomatic or have mild symptoms.

However, even in asymptomatic or mild cases, it is possible for someone who is fully vaccinated to transmit COVID-19 to others. This is particularly true when someone is infected with the highly transmissible Delta variant.

Yes, the U.S. Centers for Disease Control and Prevention (CDC) recommends that everyone 6 months and older get the updated Pfizer-BioNTech or Moderna COVID-19 vaccine, regardless of any previous COVID-19 vaccinations.

Approved by the U.S. Food and Drug Administration on Sept. 11, 2023 and recommended by the CDC on Sept. 12, 2023, the newly formulated COVID-19 vaccine targets a more recent variant of the virus than earlier vaccines. 

Learn more about the vaccine and booster shots in our COVID-19 vaccine info hub.