COVID-19 vaccine breakthrough cases in Oregon

We’ve seen some talk online about COVID-19 vaccine breakthrough cases. While these cases are rare, we’ll use this blog post to break down what a breakthrough case is, why they occur and how state and nationwide health authorities are responding.

COVID-19 vaccine breakthrough cases

COVID-19 vaccine breakthrough cases are defined as instances in which an individual tests positive for COVID-19 at least 14 days after receiving the final dose of a COVID-19 vaccine series.

As of April 2, the Oregon Health Authority (OHA) had identified 168 such cases in Oregon, including three deaths. Fortunately, the number of vaccine breakthrough cases identified represented a very small proportion of the more than 700,000 people who had been fully vaccinated statewide at that point in time. Only three deaths occurred in vaccine breakthrough cases and none of these were known to be associated with a COVID-19 variant of concern.

How state and nationwide health authorities are responding

State and local epidemiologists are continuing to track and investigate vaccine breakthrough cases and are working closely with the CDC to collect information that may provide insight into characteristics associated with COVID-19 vaccine breakthrough.

These characteristics include things like age, underlying health conditions, the type of vaccine administered and whether a variant of concern caused the breakthrough infection.

The CDC has created a national COVID-19 vaccine breakthrough REDCap database for state health department investigators to report information about breakthrough cases.

The CDC is also leading multiple vaccine effectiveness studies to ensure COVID-19 vaccines are working as expected. Oregon will be participating in these vaccine effectiveness studies.

Why vaccine breakthrough cases occur

It’s important to note that vaccine breakthrough cases are expected to occur with any vaccine because no vaccine is 100% effective.

The COVID-19 vaccines that have received Emergency Use Authorizations (EUA) from the U.S. Food and Drug Administration (FDA) have all proven to be highly effective at preventing COVID-19 and that remains true despite the small number of vaccine breakthrough cases that have occurred.

Clinical trials revealed that the Pfizer vaccine was 95% efficacious in preventing COVID-19, while the Moderna vaccine was 94.1% efficacious and the Johnson & Johnson vaccine was 66.3% efficacious.


COVID-19 vaccine breakthrough cases are rare — both in Oregon and across the country. Because no vaccine is 100% effective, vaccine breakthrough cases are anticipated to occur. Fortunately, the CDC is working alongside state and local epidemiologists to track vaccine breakthrough cases throughout the country and actively study vaccine breakthrough cases.

Importantly, breakthrough cases can be prevented through basic public health interventions, such as masking, physical distancing and avoiding social gatherings. These protective measures remain essential as long as there is significant COVID-19 circulating in our communities.

COVID-19 vaccines remain a safe and effective way to prevent yourself from getting infected with COVID-19 and returning to doing the things that you love.

For more information on the COVID-19 vaccine, visit our webpage at