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Detecting rare blood clots was a win, but US vaccine safety system still has gaps

JoNel Aleccia, Kaiser Health News on

Published in News & Features

The quick detection of an ultra-rare blood clotting reaction in some COVID-19 vaccine recipients showed the power of a federal warning system for vaccine safety issues, but experts worry that blind spots in the program could hamper detection of other unexpected side effects.

Before the pandemic began, the Food and Drug Administration had scaled back a program it used successfully to track adverse events during and after the 2009 H1N1 influenza pandemic, and the agency is still ramping up its replacement, said Dr. Robert Chen, scientific director of the Brighton Collaboration, a nonprofit global vaccine safety network.

“It’s purely bad luck they were in between systems when COVID hit,” said Chen, who helped create the existing U.S. vaccine safety systems during nearly 30 years at the Centers for Disease Control and Prevention.

FDA officials acknowledged that some data analysis won’t start for weeks or months, but said the government is watching for vaccine reactions with “state-of-the-art” systems.

“FDA and CDC have robust safety and effectiveness surveillance systems in place to monitor COVID-19 vaccines authorized for emergency use in the U.S.,” Abby Capobianco, an FDA spokesperson, wrote in an email.

No question, the nation’s vaccine surveillance system performed as expected this spring when it identified unusual cases of blood clots combined with low platelet counts in 15 people who had received Johnson & Johnson’s one-shot COVID-19 vaccine, said Dr. Jesse Goodman, a former chief scientist with the FDA. Three people died.


“The good news for a very rare event is it will pop up on VAERS,” Goodman said on a call with reporters, referring to the Vaccine Adverse Event Reporting System jointly run by the FDA and CDC since 1990.

But other potentially dangerous, unanticipated reactions to vaccines may not be so obvious in VAERS, a system that is believed to miss many potential side effects — or in the nation’s additional monitoring systems, including the Vaccine Safety Datalink and the CDC’s new phone-based tracking program, v-safe.

“It’s quite a hodgepodge of different systems of collecting data,” said Dr. Katherine Yih, a biologist and epidemiologist who specializes in vaccine surveillance at Harvard Pilgrim Health Care. “It’s worth stating that it’s not as good as it could be.”

The Vaccine Safety Datalink, though highly regarded, did not include enough vaccinations within its data from nine hospital systems covering 12 million people to catch the J&J issue, CDC officials said. And enrollment in v-safe has been less than expected, with about 6 million people enrolled by the end of March, just 6.4% of those who had been vaccinated at that point.


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