Avian Flu Diary: CDC Update: COVID-19 Vaccine Breakthrough Cases

#15,926

As we saw yesterday, in UK PHE: Impact of COVID-19 Vaccines on Mortality in England, in countries where COVID vaccinations have been successfully and substantially rolled out, COVID case numbers - and fatalities in particular - have begun to fall.

That said, no vaccination is 100% effective, in 100% of its recipients. And there remain open questions about how long vaccine protection will last, and how well current vaccines will fare against new COVID variants.

But even in cases where they don't prevent infection, there is evidence to suggest that our COVID vaccines may reduce the severity of illness. These `breakthrough infections', while not the `home run' some people were hoping for, are not unexpected.

Ten days ago, in CDC: COVID-19 Breakthrough Case Investigations and Reporting, we looked at the CDC's first weekly update on COVID-19 Breakthrough cases in fully vaccinated individuals, as reported by state and local health departments.

While it is undoubtedly a substantial undercount, as of April 20th the CDC has been notified of 7,157 breakthrough cases - a roughly 25% increase over their initial report of April 13th.

This is a reassuringly low number when compared to the nearly 100 million fully vaccinated individuals in the country, but it is a reminder that vaccination is not an ironclad guarantee of protection. Hence the need for vaccinated individuals to continue to observe some of the same social distancing measures as those who remain unvaccinated.

These breakthrough numbers will undoubtedly rise substantially over time. Even if our current vaccines should prove to be 90% effective in preventing COVID infection - and no one is claiming that - millions of breakthrough infectious would still be expected over the next year or two.

Where COVID vaccines are expected to have their greatest impact is in reducing severe disease, which should manifest itself in lower hospitalizations, and far fewer deaths. How effective they will be in preventing mild or asymptomatic infection remains to be seen.

Later today the CDC is expected to unveil new guidance for face mask wearing by fully vaccinated individuals in an outdoor environment.

In the meantime we have the following update from the CDC on breakthrough infections.

COVID-19 Breakthrough Case Investigations and Reporting

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 87 million people in the United States had been fully vaccinated as of April 20, 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 infections 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 20

As of April 20, 2021, more than 87 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 45 U.S. states and territories.

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Despite the lack of 100% protection, I'm personally grateful to be fully vaccinated, although I'm not reducing my personal NPIs (non-pharmaceutical interventions) anytime soon; I continue to wear a facemask in public, use hand sanitizer liberally, and avoid crowds whenever possible.