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What the CDC’s VAERS system is — and isn’t — good for

The database is intended to collect all possible reports of vaccine side effects, but in their raw form those reports are entirely unconfirmed and unvetted.

covid shot
You don’t have to be a doctor or a scientist to make a report to the Vaccine Adverse Event Reporting System.
REUTERS/Kamil Krzaczynski

Just over a year into vaccines being available, nearly 70 percent of Minnesotans age 5 and up have been vaccinated against COVID-19.

When it comes to the other 30 percent, there are a lot of reasons people have yet to get the vaccine: some just haven’t gotten around to it. Others face structural barriers that make it hard to access the shots. And some still have doubts about the safety and efficacy of the vaccines.

People’s doubts and fears vary in reason and origin. But some of them have been stoked — in good faith or bad — by people misinterpreting data coming from the Vaccine Adverse Event Reporting System, or VAERS, a federal database to which anyone can report their post-vaccine experiences.

It’s not just on social media where you find questions about vaccine side-effects linked to VAERS. Last week, Minnesota Rep. Glenn Gruenhagen (R-Glencoe), raised concerns he said he’d been hearing about COVID-19 vaccine safety in a state House Health Finance and Policy Committee.

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“Individuals who come to me, they’ve got a couple areas of concern when it comes to the vaccine,” Gruenhagen said. “Number one is the VAERS reports,” he said, raising questions about deaths, hospitalizations, permanent disabilities, myocarditis (heart inflammation) and miscarriages supposedly linked to COVID-19 vaccines in the reports.

“It is something that I think people look at and have concerns about,” Gruenhagen said.

Experts say drawing a direct line between VAERS reports and vaccines mischaracterizes the database and what it’s designed to do. The reports contained in VAERS are open source, anecdotal and largely unverified, and while they may indicate symptoms that occurred post-vaccine, they do not link those symptoms to vaccines in any meaningful way.

What is VAERS and why it exists

The VAERS database launched in 1990 as a way for the government to collect reports of potential negative reactions to vaccines, then analyze them in the hopes of detecting any potential safety issues early. It’s jointly managed by the Centers for Disease Control and the Food and Drug Administration.

Health care workers are required to report some adverse events and vaccine manufacturers are required to report all adverse events they’re aware of. But anyone can report an adverse event — real, perceived or totally made up — to VAERS. (It is against the law to knowingly file a false VAERS report “with the intent to mislead.”)

In that way, it’s unlike any other health sector safety tool, said Dr. Rebecca Wurtz, director of the Public Health Administration and Policy program at the University of Minnesota School of Public Health.

Because anyone can make a report, the incident reports held in VAERS vary significantly in their quality. Some are specific, some are not. Some are clearly entered by doctors who understand patients’ underlying health conditions — others are not.

“It could be as well-nuanced and thoughtful and scholarly as you want, or it could be, frankly, as crazy as you want. There is nothing that stops you from going in there and saying, ‘I grew a tentacle after I had my tetanus shot and I’m certain the shot did it,’” said Dr. Dimitri Drekonja, an associate professor and infectious disease specialist at the University of Minnesota Medical School.

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VAERS is not a systematic list of every side-effect that has happened post-vaccination. Instead, it’s a database full of anecdotes, and some types of events are more likely to be reported than others.

“By its design, it’s a biased sample, and it’s prone to both under-reporting and over-reporting,” said Dr. David Gorski, a surgical oncologist at Wayne State University who has long been writing on the misuse of VAERS by people who oppose vaccines. More mundane vaccine reactions like a sore arm or a brief fever are likely under-reported. “But on the other hand, if someone dies after a vaccine, whether the vaccine is likely to have had anything to do with it or not, you can bet it will be reported.”

Reporting is also likely up because of scrutiny and attention over the COVID-19 vaccine: people who received shots also received CDC flyers out how to report adverse events to VAERS, Gorski said.

VAERS is also not the be-all, end-all of vaccine safety monitoring in the U.S. There are other databases, including Vaccine Safety Datalink, which monitors electronic health records, and the FDA’s Sentinel program, which looks at insurance claims, that track these kinds of things, and that VAERS can be checked against.

“If there are safety signals found in VAERS, then the CDC and other scientists can use other databases to test those hypotheses to see if there might be anything to them,” Gorski said.

Correlation and causation

While VAERS reports are publicly available for anyone to read, they really aren’t designed for consumption by the masses.

One of the biggest problems for regular people trying to make sense of VAERS data is mistaking correlation (two events that have something in common – such as happening to the same person within a certain timeframe) with causation (the idea that one of the events caused the other).

Just because someone has a heart attack or gets into a car crash after going to the Mall of America doesn’t mean their health event or crash happened because they went to the Mall of America, said Dan Huff, assistant MDH commissioner, in last week’s committee hearing.

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Likewise, when something happens after a vaccine, it’s hard to know whether or not it was because they got the vaccine.

A certain number of people across the population are likely to get a fever, have a heart attack or die every day. Complex data analysis done by the CDC and other researchers — far beyond what the average citizen looking at VAERS reports can do – is required to determine whether incidents of these things happening post-vaccine rise to a level higher than what would be expected to happen at a baseline level in the population.

“What we have to see is,  is there a link between the vaccine [and the event] or is it just something that would have happened anyway,” Huff said.

Another way to think about it: Out of the U.S. population of roughly 330 million people, an average of 3 million or so people are expected to die every year, said Gorski — of old age, in car crashes, of disease or of other causes. That’s about 8,000 people per day. So if 1,000 people were reported to have died within 30 days post-vaccination, that would be significantly lower than the number expected by natural chances alone.

“A few months ago, [some people] were claiming that 20,000 died after the vaccine. That’s actually a small number compared to the baseline,” Gorski said.

In Minnesota, roughly 45,000 people died in 2019. VAERS has 435 reports of death in people who had received a COVID-19 vaccination, half which were reported in people in their 80s and up, a population that is statistically more likely to die on any given day.

Amid COVID-19, VAERS data has been misused to draw conclusions about the risk of infertility and miscarriage post-vaccination, conditions that have no proven link to COVID-19 vaccines.

Despite its potential for abuse, VAERS has shown its use over the course of the COVID-19 vaccine rollout, Drekonja said, helping to quickly identify, for example, an exceedingly rare blood clotting issue that was recorded in 54 of 17 million people who had received the Johnson & Johnson vaccine as of last April.

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“It is part of the surveillance system that was able to catch things like thrombosis after the Johnson & Johnson vaccine even though that was really an extremely rare thing,” he said.

How to approach VAERS

Because of the many limitations of VAERS, experts caution against lay people using it to draw any conclusions about the safety and efficacy of vaccines.

Instead, it’s better to think of VAERS as an effort to collect data widely about potential vaccine side-effects as part of a bigger effort by experts to understand vaccine safety.

A much more reliable source of vaccine safety information is the CDC’s page on “serious adverse events of interest,” which lists potential side effects of the COVID-19 under investigation, including rare instances of blood clots with the J&J vaccine and cases of myocarditis (also rare, and more common with COVID-19 infection than with the vaccine).

So what advice would Wurtz give to regular people trying to understand VAERS?

“To not listen to conclusions drawn by non-scientists about what the data mean,” Wurtz said.