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• Posted December 15, 2025

FDA Weighs Strongest Black Box Warning for COVID Vaccines

The U.S. Food and Drug Administration (FDA) is considering adding the strongest safety warning available to COVID-19 vaccines.

The move has alarmed many outside health experts, who say there is no scientific basis for the warning.

People familiar with the plan told CNN the FDA is weighing whether to place a black box warning on COVID vaccines. These warnings appear at the top of drug labels and are typically reserved for interventions linked to serious or life-threatening risks.

The plan is still under review and has not been finalized, officials said. It’s also unclear whether the warning would apply to all COVID vaccines, only mRNA shots, or to certain age groups.

“Unless the FDA announces it, any claim about what it will do is pure speculation,” Andrew Nixon, a spokesperson for the U.S. Department of Health and Human Services (HHS), said.

A boxed warning is the FDA’s most serious alert. These warnings appear on drugs like opioids, which carry addiction and overdose risks, and on some vaccines used for rare diseases that can cause serious side effects.

Three COVID vaccines are currently approved in the U.S. Two, made by Pfizer and Moderna, use mRNA technology. 

While most vaccines contained a weakened or dead bacteria or virus, these new vaccines introduce a molecule called messenger mRNA to train the body to mount an immune response to a virus or bacteria, according to the National Library of Medicine.

In statements issued earlier this year, both Pfizer and Moderna emphasized that their vaccines have been closely monitored by regulators worldwide. Moderna said that after more than 1 billion doses given globally, they “have not reported any new or undisclosed safety concerns in children or pregnant women.”

Studies have also shown the vaccines saved lives. One 2022 study estimated that COVID-19 vaccines prevented nearly 20 million deaths worldwide during their first year of use.

What's more, a U.S. Centers for Disease Control and Prevention (CDC) report found that during the 2024-25 season, vaccinated children had a “substantially lower risk” of COVID-related emergency and urgent care visits.

Protection was about 76% for children ages 9 months to 4 years and 56% for kiddos ages 5 to 17.

COVID-19 vaccine labels already warn about myocarditis and pericarditis, rare types of heart inflammation seen mostly in teen boys and young men.

Health officials say most patients recovered fully and cases have dropped since dosing schedules were changed.

In May, the FDA expanded existing label language to note that the highest risk has been seen in males ages 12 to 24.

What’s troubling now, public health experts say, isn’t just the idea of a new warning, but how it appears to be playing out.

Normally, things like this are reviewed publicly, often with the help of outside advisers. Several experts said they have not seen data supporting the need for a black box warning.

“I guess my concern is that in this case, there’s not a process,” Dr. Aaron Kesselheim, who studies drug regulation at Harvard University, told CNN. “There isn’t that same opportunity for discussion and good-faith review of the data on which this decision is being made."

More information

The U.S. Centers for Disease Control and Prevention has more on COVID vaccines.

SOURCE: CNN, Dec. 12, 2025