COVID-19 Breakthrough Case Investigations and Reporting

4/17/21, 10:47 AMCOVID-19 Breakthrough Case Investigations and Reporting | CDC

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Vaccines & Immunizations

COVID-19 Breakthrough Case Investigations and

Reporting

This page provides information and resources to help public health departmentspublic health departments and laboratories laboratories investigate and

report COVID-19 vaccine breakthrough cases.

Vaccine breakthrough cases are expected. Vaccine breakthrough cases are expected. COVID-19 vaccines are e!ective and are a critical tool to bring the

pandemic under control. However no vaccines are 100% e!ective 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 75 million people in the United States had been fully vaccinated as of April 14, 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 o!er 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 e!ectiveness 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 infections among people who

received COVID-19 vaccine and identify patterns or trends in:

Patient characteristics, such as age or underlying medical conditions

The speci"c vaccine that was administered

Speci"c SARS-CoV-2 variants that causes the infection

Establishing a vaccine breakthrough case deﬁnition

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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 Noti"able Diseases Surveillance System (NNDSS) to identify vaccine

breakthrough cases. Once CDC has con"rmed 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

con"rmation by the state health department.

COVID-19 vaccine breakthrough infections reported to CDC

As of April 13, 2021, more than 75 million people in the United States had been fully vaccinated against COVID-19

since December 14, 2020.

During the same time, CDC received 5,814 reports of vaccine breakthrough infections from 43 U.S. states and

territories.

Vaccine breakthrough infections were reported among people of all ages eligible for vaccination.

2,622 (45%) of the reported infections were among people ≥60 years of age.

3,752 (65%) of the people experiencing a breakthrough infection were female.

1,695 (29%) of the vaccine breakthrough infections were reported as asymptomatic.

396 (7%) people with breakthrough infections were known to be hospitalized and 74 (1%) died.

Of the 396 hospitalized patients, 133 (34%) were reported as asymptomatic or hospitalized for a reason not

related to COVID-19.

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Of the 74 fatal cases, 9 (12%) were reported as asymptomatic or the patient died due to a cause not related to

COVID-19.

Hospitalizations and deaths that are not a direct result of COVID-19 are still considered vaccine breakthrough

cases if the person was fully vaccinated and subsequently tested positive for 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 identi"ed 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 E!ective

Vaccine breakthrough cases occur in only a small percentage of vaccinated persons. To date, no unexpected

patterns have been identi"ed in the case demographics or vaccine characteristics among people with reported

vaccine breakthrough infections.

COVID-19 vaccines are e!ective. 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.

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) .

For local health departments, healthcare providers, and clinical laboratoriesFor local health departments, healthcare providers, and clinical laboratories

4/17/21, 10:47 AMCOVID-19 Breakthrough Case Investigations and Reporting | CDC

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If a possible vaccine breakthrough case is identi"ed:

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:

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), the positive specimen may still be submitted to CDC for RT-PCR and possible sequencing.

CDC will be transitioning to focus on identifying and investigating only vaccine breakthrough infections that result in

hospitalization or death and will provide additional details on reporting.

For state health departmentsFor state health departments

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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 identi"ed, 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 identi"es 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 Documents .

How to send CDC sequence data or respiratory specimens from suspected vaccine breakthroughHow to send CDC sequence data or respiratory specimens from suspected vaccine breakthrough

casescases

Resources to support submitting breakthrough case data to CDC

COVID-19 vaccine breakthrough case investigation form [2 pages]

Information for laboratories COVID-19 vaccine breakthrough case investigation [2 pages]

Information for state and local health departments COVID-19 vaccine breakthrough case investigation [2 pages]

Public health investigations of COVID-19 vaccine breakthrough cases protocol [10 pages]

Page last reviewed: April 16, 2021

Content source: National Center for Immunization and Respiratory Diseases