COVID-19 Vaccine Breakthrough Case Investigation and Reporting

CDC now recommends that people aged 65 years and older, residents in long-term care settings, and people aged 50–64 years with underlying medical conditions should receive a booster shot of Pfizer-BioNTech’s COVID-19 Vaccine at least 6 months after completing their Pfizer-BioNTech primary series. Other groups may receive a booster shot based on their individual risk and benefit. Learn more.

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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 181 million people in the United States have been fully vaccinated as of September 20, 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 September 20, 2021

As of September 20, 2021, more than 181 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 19,136 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=4,493		N=14,643
Females	1,977	(44%)	7,035	(48%)
People aged ≥65 years	3,882	(86%)	10,136	(69%)
Asymptomatic or not COVID-related**	839	(19%)	2,912	(20%)

*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.

CDC encourages local health departments, healthcare providers, and clinical laboratories that identify a COVID-19 vaccine breakthrough case to:
- Request the respiratory specimen be held for further testing.
- Report the case to the state health department where the individual resides for further investigation and reporting to the national system.
COVID-19 vaccine breakthrough cases that result in hospitalization or death should be reported to the Vaccine Adverse Event Reporting System (VAERS)external icon.

If a possible vaccine breakthrough case is identified:
- Request that the clinical or public health laboratory hold any residual respiratory specimens from the positive SARS-CoV-2 test.
- Report the available case data to NNDSS, per normal procedures.
- Review CDC’s screening questions to assess whether the case meets the COVID-19 vaccine breakthrough investigation criteria.
If the reported case meets those criteria, CDC encourages state health departments to:
- Follow the steps for initiating a COVID-19 vaccine breakthrough case investigation.
- Record the case in the COVID-19 vaccine breakthrough REDCap database.
Because CDC would like to characterize the SARS-CoV-2 lineages responsible for COVID-19 vaccine breakthrough cases, including variants, CDC requests state health departments to:
- Report sequence results from a state public health laboratory, commercial reference laboratory, or academic laboratory by entering the PANGO lineage and GenBank or GISAID accession number into the COVID-19 vaccine breakthrough REDCap database.
- If SARS-CoV-2 sequencing will not be performed locally and an acceptable clinical respiratory specimen is available, provide instructions for the testing laboratory to send the residual respiratory specimen to CDC.
- For cases with a known RT-PCR cycle threshold (Ct) value, submit only specimens with Ct value ≤28 to CDC for sequencing. (Sequencing is not feasible with higher Ct values.)
- If the Ct value is not known (e.g., positive by antigen test only or by a molecular test that does not provide a Ct value), submit the positive specimen may still be submitted to CDC for RT-PCR and possible sequencing.

CDC would like to receive sequence data and respiratory specimens from COVID-19 vaccine breakthrough cases to assess the SARS-CoV-2 lineage, including variants. When a vaccine breakthrough case is identified, the health department will contact the laboratory to request that any residual respiratory specimen from the positive test be held for sequencing at CDC.
The health department also will request the specimen ID numbers and the Ct value for positive RT-PCR results.
If SARS-CoV-2 sequencing will not be performed locally and a specimen is available, the state public health laboratory should request the residual clinical respiratory specimen for subsequent shipping to CDC.
- For cases with a known RT-PCR cycle threshold (Ct) value, submit only specimens with Ct value ≤28 to CDC for sequencing.
- If the Ct value is not known (e.g., positive by antigen test only or by a molecular test that does not provide a Ct value), the positive specimen may still be submitted to CDC for RT-PCR and potential sequencing.
If your laboratory identifies a COVID-19 vaccine breakthrough case, please report it to your state health department so it can initiate the investigation with CDC.
These instructions can also be found here: NS3 Submission Guidance Documentsexternal icon.

Resources to support submitting breakthrough case data to CDC

For more information on COVID-19 breakthrough cases:

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Page last reviewed: September 24, 2021

Content source: National Center for Immunization and Respiratory Diseases