VAERS accepts all reports of suspected adverse events, in all age groups. Patients, parents and caregivers are encouraged to report “any clinically important medical event or health problem that occurs after vaccination,” even if they’re not sure if it was a result of the vaccine. These reactions may or may not been caused by a vaccine.
These reports create a public national database that allows government scientists, and others, to rapidly detect unusual and unexpected patterns that later can be analyzed.
“It generates perhaps the most rapid type of signal if there was something really awful going on,” Dr. Susan S. Ellenberg, a professor of biostatistics, medical ethics and health policy at the University of Pennsylvania’s Perelman School of Medicine, told us.
As described on its website, VAERS can detect new, unusual or rare reactions to vaccines; monitor increases in known side effects; assess the safety of newly licensed vaccines; and identify other possible safety issues.
Dr. Walter Orenstein, associate director of the Emory Vaccine Center in Atlanta, who directed the CDC’s immunization program from 1988 to 2004, told us that VAERS’ unique capacity of generating timely signals makes it an extremely important tool.
“It is the best signal generator,” he said. “We may miss signals without VAERS.”
Orenstein said VAERS was very helpful in 1998, for example, when it detected a safety issue with the first rotavirus vaccine, RotaShield, as it was being associated with a type of bowel obstruction in infants called intussusception. After the cases were reviewed, the CDC withdrew its recommendation for that vaccine, and the manufacturer took it off the market.
More recently, as explained in a 2015 study co-authored by scientists from the CDC and FDA, VAERS detected unusual reporting for febrile seizures in young children following a flu shot during the 2010-2011 season. After those episodes, the CDC started listing febrile seizures as a possible side effect of some vaccines for infants and children up to 5 years old.
VAERS Causation Limitation
Although VAERS is great at creating alerts for researchers to follow up, experts agree the database has multiple weaknesses.
“The biggest limitation is it usually cannot help us assess causation, it provides signals,” Orenstein said.
As we said, everyone is encouraged to report any medical event or health problem, even if they’re not sure it was caused by a vaccine. The event may have been caused by an underlying medical condition, by a medication or drug taken at the same time, or simply by chance.
When VAERS detects something unusual, those signals are investigated by scientists and other vaccine surveillance systems, such as the Vaccine Safety Datalink, a collaboration between the CDC’s Immunization Safety Office and nine health care organizations, or the CDC’s Clinical Immunization Safety Assessment Project, a network of vaccine safety experts, including those at seven medical research centers, to evaluate causality. In the case of COVID-19 vaccines, VAERS is just one of several vaccine safety monitoring systems the government has in place.
According to a November 2020 VAERS report, less than 15% of all the events reported to the database describe “serious events, such as hospitalizations, life-threatening illnesses, or deaths.” When a death is reported, the agency collects information, including medical records, autopsy reports and death certificates, and a qualified physician determines the cause of death.
“Just because somebody reports death doesn’t mean that the vaccine caused the death. So we don’t use VAERS to determine death rates or anything concerning death,” a CDC spokesperson told us previously.
The vast majority of events reported for COVID-19 vaccines haven’t been serious.
In the latest safety update presented by the CDC’s Vaccine Safety Team to the Advisory Committee on Immunization Practices on March 1, Dr. Tom Shimabukuro reported that as of Feb. 16, 94% of the reports submitted to VAERS after the administration of the Moderna and Pfizer/BioNTech vaccines were for non-serious events such as headaches, fever, chills and fatigue. The reports of serious events, such as anaphylaxis, heart attacks and strokes, were assessed by vaccine surveillance systems. Except for cases of anaphylaxis, which were rare, the CDC reported no safety concerns were detected, meaning there was no cause and effect relationship between the vaccines and the reported adverse events.
“People die, unfortunately, without vaccination,” Orenstein told us. “The issue is to determine where the vaccine enhances that risk of death and not, and that’s why we have this very careful system.”
He said the fact that VAERS doesn’t determine causation is difficult for people to understand, despite all the disclaimers on its website and brochures.
“There is a natural human tendency — plus it has served us well — if event B follows event A, then event A caused event B. I mean, we don’t need a scientific study to know if you jump out of a plane without a parachute, you’re going to be in trouble,” Orenstein said. “I think the issue here is the clinical syndromes that are occurring and [are being] reported to VAERS can also occur without a vaccine. And that’s what complicates things.”
Other VAERS Limitations
The fact that VAERS cannot assess causality is not its only weakness.
“It’s the worst possible data that you could possibly imagine because there’s so many uncertainties about it,” said Ellenberg, who analyzed VAERS data for 11 years as director of the FDA’s Office of Biostatistics and Epidemiology in the Center for Biologics Evaluation and Research.
One of the major problems, she said, is that there’s no control group to study because unvaccinated people do not report adverse events to VAERS. Therefore, there’s no way to determine if the number of reported events is different from the number that would have been observed without vaccination.
Take the 2,509 reports of death filed to VAERS as of March 29, which represent 0.0017% of those who had received a COVID-19 vaccine. People die every day for any number of reasons. In 2019, for example, 0.8% of the U.S. population died from any cause, according to the CDC. That was before the coronavirus pandemic.
“You’re going to have deaths that had nothing to do with the vaccines,” Ellenberg told us.
Deaths unrelated to COVID-19 occurred during the vaccine clinical trials, she said. So she expected to see deaths unrelated to the vaccines among the general population, especially considering that older people and people with underlying medical conditions are getting vaccinated first.
Another issue, Ellenberg said, is the accuracy and completeness of the data because anything that anybody reports goes into the database. A person could file a report omitting important details, such as which vaccine they got. Or someone could even report a false event, or report an event without having received a vaccine in the first place — although filing a false VAERS report intentionally is a violation of federal law punishable by fine and imprisonment.
“So you know, if somebody reports that they went skiing and broke their leg, and you know, two years before they had gotten a flu shot, they could report that to VAERS,” she said.
As experts have told us before, reports to VAERS tend to increase when there’s more awareness of the vaccine or more publicity around specific side effects. For example, Ellenberg said, there was an increase in the number of VAERS reports following approval of a Lyme disease vaccine in the late 1990s and a class-action lawsuit against the vaccine manufacturer, which withdrew the vaccine from the market even though “the adverse event rate was not shown to be elevated among vaccine recipients,” according to the National Institute of Allergy and Infectious Diseases.
VAERS data aren’t meant to allow safety comparisons between vaccines, but multiple social media posts make such false comparisons anyway. As a disclaimer on the VAERS website states: “The number of reports alone cannot be interpreted or used to reach conclusions about the existence, severity, frequency, or rates of problems associated with vaccines.”
Other limitations include underreporting, when people don’t report serious events happening after vaccines.
“In addition, it is often the case that more than one vaccine was administered, making it difficult to know to which of the vaccines the event might be attributed,” the VAERS user guide says.
Experts agree that even with all of VAERS’ weaknesses, having a system with the potential for identifying new adverse effects and signals that can be followed up with more data is still worth having. That’s especially true in cases when an emergency use authorization has been issued, and there has been less time to monitor possible adverse events before a vaccine gets on the market.
Because of the urgency of the ongoing pandemic, the FDA required at least two months of follow-up data on half or more of the participants in phase 3 clinical trials for a COVID-19 vaccine to get an emergency use authorization. As we’ve explained, full licensure requires a minimum of six months, though experts say there’s little reason to think more time would uncover safety concerns.
“There are people who have said VAERS, and those kinds of systems are worthless, we shouldn’t even bother with them,” Ellenberg said. “I don’t agree with that.”
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