Breakthrough cases: Tracking disease infection after vaccination

In public health, a “breakthrough case” is when a fully vaccinated person later gets the disease they were vaccinated for. No vaccine provides 100 percent protection against infection, so breakthrough cases are not new, and not unique, to COVID-19. There have been reports of COVID-19 breakthrough cases in South Carolina and throughout the U.S., and this is not unexpected. 

COVID-19 vaccines are very effective in preventing mild symptoms, severe disease, and hospitalizations due to COVID-19 disease. Fully vaccinated people can resume activities without wearing a mask under most conditions. Fully vaccinated people will still need to follow guidance at their workplace and local businesses, and requirements for public transportation. Until more people are immune to COVID-19, this will help prevent exposure to the virus and unknowingly spreading it to others.

Because fully vaccinated people usually have some immunity against the disease, breakthrough cases usually have either no symptoms or mild symptoms.  A breakthrough case occurs when an individual has had a lower immune response from the vaccine. No vaccine is 100 percent effective. 

The Centers for Disease Control and Prevention (CDC) is currently investigating all reports of COVID-19 breakthrough cases. Breakthrough cases are studied as part of the CDC’s ongoing research to assess how COVID-19 vaccines work in real-world conditions. According to the CDC, assessing how vaccines work in the real world is important to:

  • Learn if vaccines offer the same protection seen in clinical trials.
  • Adjust vaccine recommendations, as needed.
  • Learn why and how often breakthrough cases (people getting sick after vaccination) occur.
  • Learn how vaccines protect against COVID-19 variants.

People who are fully vaccinated do not need to quarantine or be tested for COVID-19 if they have no symptoms. If they have symptoms, they should be tested, and if positive, will need to follow all of the recommended isolation procedures.

Because the vaccines require about two weeks to become effective, a person is not considered fully vaccinated until two weeks after they completed the recommended number of doses for the vaccine they received. A person who tests positive for COVID-19 between their first and second doses of two-dose vaccines, or a person who tests positive before the two-week period after their final dose, is not considered a breakthrough case.

DHEC continues to work closely with the CDC during these ongoing national and international efforts to accurately identify breakthrough cases. DHEC will continue to keep South Carolinians updated and informed and new information will be provided as it becomes available.


COVID-19 Infectious Diseases Statewide