COVID-19 vaccines are effective. However, a small percentage of people who are fully vaccinated will still get COVID-19 if they are exposed to the virus that causes it. These are called “vaccine breakthrough cases.”
Vaccine breakthrough cases are expected. However, no vaccines are 100% effective at preventing illness in vaccinated people. There will be a small percentage of fully vaccinated people who still get sick, are hospitalized, or die from COVID-19.
For the purpose of this surveillance, a vaccine breakthrough infection is defined as the detection of SARS-CoV-2 RNA or antigen in a respiratory specimen collected from a person ≥14 days after they have completed all recommended doses of a U.S. Food and Drug Administration (FDA)-authorized COVID-19 vaccine.
As of May 1, 2021, CDC transitioned from monitoring all reported vaccine breakthrough cases to focus on identifying and investigating only hospitalized or fatal cases due to any cause.
As expected, this change is happening at a time when thousands of breakthrough cases are being reported in the fully vaccinated.

Of the millions of people across the country who have been fully vaccinated against COVID-19, the U.S. Centers for Disease Control and Prevention has only recorded a few thousand breakthrough cases of the disease, the agency said Thursday.
Vaccine breakthrough cases are expected. However, no vaccines are 100% effective at preventing illness in vaccinated people. There will be a small percentage of fully vaccinated people who still get sick, are hospitalized, or die from COVID-19.
For the purpose of this surveillance, a vaccine breakthrough infection is defined as the detection of SARS-CoV-2 RNA or antigen in a respiratory specimen collected from a person ≥14 days after they have completed all recommended doses of a U.S. Food and Drug Administration (FDA)-authorized COVID-19 vaccine.
As of May 1, 2021, CDC transitioned from monitoring all reported vaccine breakthrough cases to focus on identifying and investigating only hospitalized or fatal cases due to any cause.
As expected, this change is happening at a time when thousands of breakthrough cases are being reported in the fully vaccinated.
Of the millions of people across the country who have been fully vaccinated against COVID-19, the U.S. Centers for Disease Control and Prevention has only recorded a few thousand breakthrough cases of the disease, the agency said Thursday.