Breakthrough cases: Tracking disease infection after vaccination

Updated Tuesday, September 14, 2021

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. 


Currently, DHEC is reporting COVID-19 vaccine breakthrough cases who were hospitalized and/or died to CDC per the reporting change that occurred on May 1, 2021. These reports are based on information received from reporting partners (e.g., hospitals, other healthcare providers). DHEC is also analyzing COVID-19 case data to estimate the total number of vaccine breakthrough cases. To perform this analysis, DHEC uses information a person voluntarily provides about their vaccination status during a case investigation.

Total breakthrough cases*¥
 

7,755

Total breakthrough hospitalizations and/or deaths*§

662

Total breakthrough hospitalizations*§
 

640

Total breakthrough deaths*§
 

173

Percent of Fully Vaccinated People who have a Breakthrough Infection

0.3694%

Percent of Fully Vaccinated People who were Hospitalized and/or Died due to COVID-19

0.0315%

Percent of Fully Vaccinated People who were Hospitalized due to COVID-19

0.0305%

Percent of Fully Vaccinated People who Died due to COVID-19
 

0.0082%

* Data as of September 7, 2021; all data are provisional

¥ Data from self-reported vaccine status

§ Vaccine breakthrough cases can be in one or both of the categories listed in the table above (hospitalizations, deaths). Therefore, the number shown in the total column for hospitalizations and/or deaths may not directly equal the number of breakthrough hospitalizations plus the number of breakthrough deaths.


COVID-19 vaccines are effective and a critical tool in bringing this pandemic to an end. However, no vaccine is 100 percent effective and there will be a small percentage of COVID-19 cases, hospitalizations, and deaths among fully vaccinated individuals. Despite this limitation, there is evidence that vaccination makes the illness less severe for those who are vaccinated and still get sick.

Because the vaccines require about two weeks to reach their maximum effectiveness, a person is not considered fully vaccinated until two weeks after they completed the recommended number of doses for the vaccine they received. Therefore, for public health surveillance purposes, a case of COVID-19 vaccine breakthrough is defined as someone who tests positive (PCR or antigen) for COVID-19 14 days or more after the person completed all recommended doses of an FDA-authorized COVID-19 vaccine. 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.

Since February 2021, DHEC has been receiving reports of COVID-19 vaccine breakthrough cases and transmitting those reports to the Centers for Disease Control and Prevention (CDC). However, as of May 1, 2021, the CDC transitioned from monitoring all vaccine breakthrough cases to focus on identifying and investigating only hospitalized or fatal cases due to any cause. Breakthrough cases are investigated 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 the two-week period after their final dose) occur.
  • Learn how vaccines protect against COVID-19 variants.

People who are fully vaccinated and have close contact with someone with COVID-19 should get tested 3-5 days after the date of their exposure and wear a mask in public, indoor settings for 14 days after exposure or until they receive a negative test result. CDC outlines more information about the activities that fully vaccinated individuals can participate in.

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.

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COVID-19 Infectious Diseases Statewide