CDC clarifies that it will continue to investigate mild post-vaccine cases of COVID-19

The U.S. Centers for Disease Control and Prevention offered clarification this week on its post-vaccine COVID-19 monitoring plans, stating that it will continue to monitor mild cases of post-vaccine COVID-19 rather than shifting to tracking only severe infections in those who have already been vaccinated.

On its website, the CDC appeared poised to begin "identifying and investigating hospitalized or fatal vaccine breakthrough cases" exclusively, ignoring asymptomatic or more mild cases in that category.

 A "breakthrough case" is a medical term for an infection with any disease that occurs after an individual has been vaccinated against it. The U.S. has recorded several thousand breakthrough infections of COVID-19 among the tens of millions of individuals vaccinated against the disease. 

"As of May 1, 2021, CDC transitioned from monitoring all reported vaccine breakthrough cases to focus on identifying and investigating only hospitalized or fatal cases due to any cause," the agency said on its website.

It claimed that the shift "will help maximize the quality of the data collected on cases of greatest clinical and public health importance."

Yet Martha Sharan, a spokeswoman for the CDC's Division of Healthcare Quality Promotion, claimed that the agency would still continue to monitor all breakthrough cases rather than "only" the most severe ones. 

"CDC has a breakthrough team that will collect data and study vaccine breakthrough cases in hospitalized or fatal cases to figure out why someone is sick enough to be hospitalized or die after being fully vaccinated," she said.  

"CDC [also] has a vaccine effectiveness team that will collect data and study vaccine breakthrough infections in patients with asymptomatic and milder illness," she added. 

Asked why the agency's website stated that the CDC was moving to focus only on severe cases, Sharan said the webpage in question was "only identifying the work of one CDC team" that is “only focusing on vaccine breakthrough cases in hospitalized or fatal cases so they can get more complete and better data on the cases that have the highest clinical and public health significance." 

“This comes after CDC experts looked at all of the infections for a period of time (Jan-April) and did not see any trends, unusual patterns, or concerning signals among the breakthrough cases," she said. 

The revelation comes after widespread reporting, including in the New York Times and elsewhere, that the agency had "stopped investigating breakthrough infections among fully vaccinated people unless they become so sick that they are hospitalized or die," as the Times put it.

Asked what the CDC meant by investigating, Sharan said the CDC's investigations into severe cases will include "hospitalized or fatal cases due to any cause."

Sharan said that the agency "will focus on breakthrough cases in hospitalized patients who were symptomatic and tested positive for COVID, and those who were asymptomatic, but during the course of their hospitalization for other medical conditions, it was discovered that they were COVID-positive.”

"The same is true for fatalities, we will focus on patients who died with COVID, regardless of whether they died of COVID," she added. 

The practice of conflating patients suffering from COVID-19 illness with those who merely test positive for the underlying virus has been a source of controversy throughout the pandemic, particularly during the summer and winter surges when hospital census reports were high and testing levels were significantly elevated over their current rate.