Fact Check – What is the US Vaccine Adverse Event Reporting System (VAERS)?


Since its inception in 1990, the Vaccine Adverse Event Reporting System (VAERS) of the United States Centers for Disease Control and Prevention (CDC) has provided publicly available data on all adverse events reported following vaccination.

Since the arrival of COVID-19 vaccines, information in the VAERS system has been frequently referenced by those who question the safety of vaccines.

The VAERS website includes disclaimers stating that reports may contain “incomplete, inaccurate, incidental or unverifiable” information and requires users to acknowledge these limitations. However, many social media posts encountered by Reuters Fact Check did not mention that reports in VAERS can be entered by anyone and are not deemed to show a causal link to a vaccine until they are known. have not been verified by the CDC.


From 1990 to 2001, VAERS data was only accessible through a Freedom of Information Act (FOIA, www.foia.gov/ ). In 2001, the data was made available on the VAERS website (vaers.hhs.gov/data.html), then moved to CDC Wonder (wonder.cdc.gov/vaers.html) in 2006, where it is still hosted. Submissions for VAERS reports remain through vaers.hss.gov.

CDC spokeswoman Martha Sharan told Reuters by email: “Transparency has always been a concern for VAERS, and with that in mind, the decision was made to make VAERS data publicly available as soon as possible. the first steps”.


When an adverse event report is filed in VAERS, it is processed and reviewed by certified coders, according to Sharan. The report is given a code based on the description given by the person who filed it and enters a database made available to the CDC and the FDA, which is updated daily.

Each report is labeled as a serious or non-serious adverse event. Serious events are defined as “death, life-threatening illness, hospitalization or prolongation of hospitalization, permanent disability, birth defects or birth defects” by the Code of Federal Regulations (here).

The CDC requests and reviews medical records, including hospital records, clinical records, death certificates, and autopsy reports, for each report labeled as “serious.”

VAERS staff are not deciding whether the vaccine caused the adverse event. To determine if there is a potential safety issue signal for a vaccine, statistical methods are used.

“If a safety issue is detected by VAERS, more detailed quantitative analyzes are performed using more robust analytical systems, such as the Vaccine Safety Datalink,” Sharan explained. “Such analyzes can determine whether there is a statistically significant association between the vaccine and the adverse event in question.”

When a safety issue is recognized for the vaccine, the FDA and the vaccine manufacturer work together to find a solution based on the safety issue, whether it is a problem with a specific batch of vaccine, the manufacture or the vaccine itself.

An FDA spokesperson told Reuters via email about the CDC’s Vaccine Safety Datalink (VSD) project or the Clinical Immunization Safety Assessment (CISA) project, saying, “These systems do not have the same limitations as VAERS. and are used to help assess health risks and possible connections between adverse events and a vaccine.

You will find more information about these systems here .

For example, “In the case of anaphylaxis, thrombosis with thrombocytopenia syndrome, and GBS after the Janssen COVID-19 vaccine and myocarditis/pericarditis after the Pfizer-BioNTech and Moderna COVID-19 vaccines, the FDA has worked with companies to update the information in the fact sheet. for Health Care Providers Administering Vaccines (Vaccine Providers) and the Information Sheet for Beneficiaries and Caregivers for each of the vaccines with information about these potential adverse events,” the FDA said.


The ability for anyone to report to VAERS is both an important part of its transparency and a limitation. Reuters has reviewed numerous examples of unverified information that has been widely shared on social media – such as the story of a two-year-old child who allegedly died during the Pfizer-BioNTech COVID-19 vaccine trial at children (here).

Participants in Pfizer’s clinical trial, which included children as young as six months, only started a month after the two-year-old in Virginia reportedly received Pfizer’s COVID-19 vaccine on February 25. , making it impossible for that child to have received a dose. A CDC spokesperson told Reuters by telephone that the report had therefore been removed from the database.

Dr. Dan Salmon, director of the Institute for Vaccine Safety at the Johns Hopkins Bloomberg School of Public Health, told Reuters by email of the risks anyone can report to VAERS.

“If I got a flu shot and my dog ​​was hit by a car, I could report it to VAERS and it would end up in a publicly available database,” Salmon said.

The data is misinterpreted and has led to widespread sharing of medical information online.

For example, Fox News host Tucker Carlson said on a show (here) on May 5, 2021 that more than 3,362 Americans had died from the COVID-19 vaccine between the end of December 2020 and April 2021. But he was referring to VAERS reports, not CDC-verified deaths.

Dr. Robert Leo Murphy, executive director of the Institute for Global Health at Northwestern University, told Reuters by phone that users should be careful in interpreting the raw data because investigation is required to determine causation.


Dr. Stephen Kissler, a researcher in the Department of Immunology and Infectious Diseases at the Harvard TH Chan School of Public Health, said on a media call (here) that public accessibility of data is very important.

“A knee-jerk reaction might be to say, well, maybe we shouldn’t make this data as publicly available as it is, or maybe it shouldn’t be as detailed, but I really hesitant to go in that direction because I really think that empowering people to make data-based decisions about their health and the health of the community, making data accessible is really important,” said Kissler.

Kissler said he believes VAERS is extremely beneficial to the medical community in prompting research into possible links between the vaccine and adverse events that may be suggested by the database.

According to Murphy, VAERS can be useful for flagging adverse events that may not have appeared or been noticed during clinical studies. (Inevitably, a clinical trial will reach a smaller sample of individuals than a nationwide vaccination campaign, for example. A system like VAERS can help detect any other potential side effects.)


Giving members of the public the ability to view all user reports is both a strength and a challenge of the system, according to global health scientist Dr. Christin Gilmer. Possible database improvements could include watermarking information, debunking fake entries before they go viral, and requiring users to undergo training before accessing data.

“For someone just looking at the data, who may not be aware of these caveats about using the data that they may not represent a causal link between vaccination and the health effects, it can be very alarming, and it may seem like the vaccine is causing all these different kinds of health effects,” Kissler said.

“Currently, it is possible to download this data from VAERS and look at adverse events following vaccination, but that does not put it in the context of the frequency of these adverse events in the general population,” Kissler said. . “That kind of thing is what I’d like to see.”

“We need to strike a balance between transparency and proactiveness to prevent VAERS reports from being the cause of people avoiding vaccines due to misinformation,” Gilmer said.

This article was produced by the Reuters Fact Check team. Learn more about our fact-checking work here.


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