COVID-19 Breakthrough Case Investigations 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 vaccines are 100% effective at preventing illness. There will be a small percentage of people who are fully vaccinated who still get sick, are hospitalized, or die from COVID-19.
  • More than 95 million people in the United States had been fully vaccinated as of April 26, 2021. Like with other vaccines, symptomatic vaccine breakthrough cases will occur, even though the vaccines are working as expected. Asymptomatic infections among vaccinated people also will occur.
  • There is some evidence that vaccination may make illness less severe.
  • 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. However, variants will cause some of these vaccine breakthrough cases.

What CDC is doing

CDC is leading multiple vaccine effectiveness studies to ensure COVID-19 vaccines are working as expected. In addition, CDC is coordinating with state and local health departments to investigate SARS-CoV-2 infectionspdf icon among people who received COVID-19 vaccine and identify patterns or trends in:

  • Patient characteristics, such as age or underlying medical conditions
  • The specific vaccine that was administered
  • Specific SARS-CoV-2 variants that causes the infection

Establishing a vaccine breakthrough case definition

A person who has SARS-CoV-2 RNA or antigen detected on a respiratory specimen collected ≥14 days after completing the primary series of a U.S. Food and Drug Administration (FDA)-authorized COVID-19 vaccine.

Identifying and investigating COVID-19 vaccine breakthrough cases

State health departments report vaccine breakthrough cases to CDC. CDC monitors reported cases for clustering by patient demographics, geographic location, time since vaccination, vaccine type or lot number, and SARS-CoV-2 lineage.

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.

In the coming weeks, CDC will transition from monitoring all reported vaccine breakthrough cases to focus on identifying and investigating only vaccine breakthrough infections that result in hospitalization or death. This shift will help maximize the quality of the data collected on cases of greatest clinical and public health importance.

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

  • CDC has 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.
  • 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 department will stop reporting cases directly into the national COVID-19 vaccine breakthrough REDCap database. CDC will upload the available data reported to NNDSS into the COVID-19 vaccine breakthrough REDCap database for further review and confirmation by the state health department.

COVID-19 vaccine breakthrough infections reported to CDC as of April 26

As of April 26, 2021, more than 95 million people in the United States had been fully vaccinated against COVID-19. During the same time, CDC received reports of vaccine breakthrough infections from 46 U.S. states and territories.

Total number of vaccine breakthrough infections reported to CDC
Total number of vaccine breakthrough infections reported to CDC 9,245
Females 5,827 (63%)
People aged ≥60 years 4,245 (45%)
Asymptomatic infections 2,525 (27%)
Hospitalizations* 835 (9%)
Deaths† 132 (1%)

*241 (29%) of the 835 hospitalizations were reported as asymptomatic or not related to COVID-19.
†20 (15%) of the 132 fatal cases were reported as asymptomatic or not related to COVID-19.

How to interpret these data

It is important to note that reported vaccine breakthrough cases will represent an undercount. This surveillance system is passive and relies on voluntary reporting from state health departments which may not be complete.  Also, not all real-world breakthrough cases will be identified because of lack of testing. This is particularly true in instances of asymptomatic or mild illness. These surveillance data are a snapshot and help identify patterns and look for signals among vaccine breakthrough cases.

As CDC and state health departments shift to focus only on investigating vaccine breakthrough cases that result in hospitalization or death, those data will be regularly updated and posted every Friday.

COVID-19 Vaccines are Effective

  • Vaccine breakthrough cases occur in only a small percentage of vaccinated persons. 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 all eligible people get a COVID-19 vaccine as soon as one is available to them.
  • CDC recommends that fully vaccinated people continue take steps to protect themselves and others in many situations, like wearing a mask, maintaining an appropriate social distance from others, avoiding crowds and poorly ventilated spaces, and washing their hands often.

For more information on COVID-19 breakthrough cases: What You Should Know About the Possibility of COVID-19 Illness After Vaccination

Page last reviewed: April 30, 2021