COVID-19 Vaccine Breakthrough Case Investigation and Reporting

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This page provides information and resources to help public health departments and laboratories investigate and report COVID-19 vaccine breakthrough cases.

  • Vaccine breakthrough cases are expected. COVID-19 vaccines are effective and are a critical tool to bring the pandemic under control; however, no vaccine is 100% effective at preventing illness. Some fully vaccinated people will get sick, and some will even be hospitalized or die from COVID-19. However, there is evidence that vaccination may make illness less severe for those who are vaccinated and still get sick. The risk of infection, hospitalization, and death are all much lower in vaccinated people compared to unvaccinated.
  • More than 189 million people in the United States have been fully vaccinated as of October 18, 2021. CDC is monitoring these cases among vaccinated persons and evaluating trends in order to better understand who is at risk for severe COVID-19 following vaccine breakthrough infection. Vaccinated people have also experienced asymptomatic infections.
  • Current data suggest that COVID-19 vaccines authorized for use in the United States offer protection against most SARS-CoV-2 variants circulating in the United States.

What CDC is doing

CDC is leading multiple vaccine effectiveness studies and monitoring vaccine breakthroughs from a network of states to understand how COVID-19 vaccines are working and to identify patterns or trends in:

  • Patients’ characteristics, such as age or underlying medical conditions
  • The specific vaccine that patients received
  • Which SARS-CoV-2 variants are causing the infection

Defining a vaccine breakthrough infection

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.

Identifying and investigating hospitalized or fatal vaccine breakthrough cases

CDC monitors reported hospitalized or fatal vaccine breakthrough cases for clustering by patient demographics, geographic location, time since vaccination, vaccine type, and SARS-CoV-2 lineage. Reported data include hospitalized or fatal vaccine breakthrough cases due to any cause, including causes not related to COVID-19.

To the fullest extent possible, respiratory specimens that test positive for SARS-CoV-2 RNA are collected for genomic sequencing to identify the virus lineage that caused the infection.

Developing a data access and management system for reporting COVID-19 vaccine breakthrough cases

CDC developed a national COVID-19 vaccine breakthrough REDCap database where designated state health department investigators can enter, store, and manage data for cases in their jurisdiction. State health departments have full access to data for cases reported from their jurisdiction.

State health departments voluntarily report vaccine breakthrough cases to CDC. On May 1, 2021, after collecting data on thousands of vaccine breakthrough infections, CDC changed the focus of how it uses data from this reporting system. One of the strengths of this system is collecting data on severe cases of vaccine breakthrough COVID-19 since it is likely that most of these types of vaccine breakthrough cases seek medical care and are diagnosed and reported as a COVID-19 case. CDC relies on a variety of additional approaches to comprehensively monitor vaccine impact. Previous data on all vaccine breakthrough cases reported to CDC from January–April 2021 are available.

Ultimately, CDC will use the National Notifiable Diseases Surveillance System (NNDSS) to identify vaccine breakthrough cases. Once CDC has confirmed that a state can report vaccination history data to NNDSS, CDC will identify vaccine breakthrough cases through that system. At that time, the state health departments can stop reporting cases directly into the REDCap database. After this change, CDC will upload the available data reported to NNDSS into the REDCap database for further review and confirmation by the state health department.

Hospitalized or fatal COVID-19 vaccine breakthrough cases reported to CDC as of October 18, 2021

As of October 18, 2021, more than 189 million people in the United States had been fully vaccinated against COVID-19.

During the same time, CDC received reports from 50 U.S. states and territories of 41,127 patients with COVID-19 vaccine breakthrough infection who were hospitalized or died.

Total number of vaccine breakthrough infections reported to CDC
Deaths Hospitalized, non-fatal*
Total N=10,857 N=30,270
Females 4,619 (43%) 14,453 (48%)
People aged ≥65 years 9,172 (85%) 20,008 (66%)
Asymptomatic or not COVID-related** 2,299 (21%) 7,866 (26%)

*This table separates all reported vaccine breakthrough infections that resulted in hospitalization and/or death into two columns.  While most deaths were also among hospitalized individuals, a small number were not.

**Includes cases in which the patient did not have symptoms of COVID-19, or their hospitalization or death was not COVID-related. For example, people may be hospitalized for reasons other than COVID-19, such as an auto accident, and test positive when screened upon hospital admission.

Previous data on all vaccine breakthrough cases reported to CDC from January–April 2021 are available.

How to interpret these data

The number of COVID-19 vaccine breakthrough infections reported to CDC are an undercount of all SARS-CoV-2 infections among fully vaccinated persons, especially of asymptomatic or mild infections. National surveillance relies on passive and voluntary reporting, and data are not complete or representative. These surveillance data are a snapshot and help identify patterns and look for signals among vaccine breakthrough cases.

Information on patients with vaccine breakthrough infection who were hospitalized or died will continue to be updated. Studies are being conducted in multiple U.S. sites that will include information on all vaccine breakthrough infections regardless of clinical status to supplement the national surveillance.

COVID-19 vaccines are effective

  • To date, no unexpected patterns have been identified in the case demographics or vaccine characteristics among people with reported vaccine breakthrough infections.
  • COVID-19 vaccines are effective. CDC recommends that everyone 12 years of age and older get a COVID-19 vaccine as soon as they can.
  • A vaccine breakthrough infection happens when a fully vaccinated person gets infected with COVID-19. People with vaccine breakthrough infections may spread COVID-19 to others.
  • Even if you are fully vaccinated, if you live in an area with substantial or high transmission of COVID-19, you will be better protected if you wear a mask when you are in indoor public places.
  • Currently, CDC is recommending that moderately to severely immunocompromised people receive an additional dose of mRNA COVID-19 vaccine at least 28 days after a second dose of Pfizer-BioNTech COVID-19 vaccine or Moderna COVID-19 vaccine.
Page last reviewed: October 15, 2021