Clinical trials brought us COVID vaccines, but we’re in largescale population ‘trials’ now and will learn more

Jake Ellison

Scientists can learn a lot in a controlled clinical trial involving tens of thousands of people, such as the COVID-19 vaccine trials that led to their approval, but we will all learn a lot more as hundreds of millions of people are vaccinated. And, some of what might turn up in this population-based data are adverse side effects, such as the blood clotting suffered by nearly 20 people out of roughly 8 million who received the Johnson & Johnson vaccine.

Clinical trials brought us COVID vaccines, but we’re in largescale population ‘trials’ now and will learn more

Larry Corey

“When a mass vaccination campaign is rolled out, adverse events are observed more acutely and more accurately than during the slow trickle that goes with any other kind of vaccine or drug distribution. The infrequent becomes more frequent because the number of people vaccinated in a very short time is so large — a one-in-a-million problem becomes one per day rather than one every two to six months,” writes the University of Washington’s Dr. Larry Corey in a recent COVID-19 Vaccine Matters blog, jointly produced by Johns Hopkins University and the UW.

The key to catching adverse effects is an effective surveillance system, which worked in the blood-clotting case and must continue to be supported with time, energy and resources.

“The advantage we have at this point is that we know how to diagnose and treat it, so there’s at least a potential to lessen the impact of the disease,” Corey wrote in the commentary. “A thorough review of the risk benefit of the vaccines was performed by both the CDC and the FDA and both of these organizations advised that people should be alerted about the possibility of (blood clotting) and to seek medical evaluation if they experience prolonged abdominal pain, worsening headache, or shortness of breath in the days following vaccination.”

This should improve public confidence that these vaccines, including the Johnson & Johnson vaccine which was put back into circulation, are still being monitored for effectiveness and safety. And, Corey points out, while adverse effects will be investigated and vaccines evaluated in light of them, the risk-to-benefit ratio of the vaccines needs to be kept in perspective. After all, the odds of being hit by a car are about one in 4,292 and dying as a result are about one in 47,273.

“Clinical trials have given us a wealth of information about the efficacy and safety profile of vaccines for COVID-19. But the work of gathering evidence and weighing results in the context of an ongoing pandemic isn’t done,” said Corey.

To read this and other articles by Corey and other experts, visit the COVID-19 Vaccine Matters blog series created by Johns Hopkins and the UW as an outcome of the joint symposium — Preserving the Scientific Integrity of Getting to COVID-19 Vaccines: From Clinical Trials to Public Allocation — the two universities hosted in October.

Dr. Larry Corey is the leader of the COVID-19 Prevention Network (CoVPN ) Operations Center, which was formed by the National Institute of Allergy and Infectious Diseases at the U.S. National Institutes of Health to respond to the global pandemic and the Chair of the ACTIV COVID 19 Vaccine Clinical Trials Working Group. He is a Professor of Medicine and Virology at University of Washington and a Professor in the Vaccine and Infectious Disease Division and past President and Director of Fred Hutchinson Cancer Research Center.


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