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Misleading to compare the safety of COVID-19 and flu vaccines based solely on VAERS reports; VAERS reports alone cannot demonstrate that a vaccine caused an adverse event

Posted on:  2021-02-17

Key takeaway

Pfizer-BioNTech and Moderna COVID-19 vaccines demonstrated a high level of safety and efficacy during clinical trials in order to receive emergency use authorization from the U.S. Food and Drug Administration. Extensive post-approval monitoring also indicates that the vaccines are safe. Apart from severe allergic reactions (anaphylaxis), the data so far doesn’t indicate that the vaccines cause severe side effects in the general population. The U.S. Vaccine Adverse Events Reporting System (VAERS) is an important tool for monitoring vaccine safety, but VAERS reports alone don’t demonstrate that a vaccine caused the adverse event. Further investigation of reported deaths found no causal link with COVID-19 vaccines.

Reviewed content


One person is 300 to 900 times “more likely to die” after getting the COVID-19 vaccine than the flu vaccine; “Adverse events are widely underreported”

Source: Instagram, Twitter/X, Alex Berenson, 2021-02-14

Verdict detail

Misleading: The U.S. Vaccine Adverse Events Reporting System (VAERS) records adverse events occurring after vaccination. However, VAERS reports alone cannot demonstrate that a vaccine caused the adverse event nor whether one vaccine is safer than another.
Inadequate support: Careful investigation found no evidence that COVID-19 vaccines caused or contributed to any of the deaths reported to VAERS.

Full Claim

One person is 300 to 900 times “more likely to die” after getting the COVID-19 vaccine than the flu vaccine; “Adverse events are widely underreported”


With the worldwide rollout of COVID-19 vaccines, claims that the vaccines caused severe adverse events or deaths spread on social media. A meme published on 15 February 2021 claimed that a person is 300 to 900 times “more likely to die” after receiving the COVID-19 vaccine than after getting the flu vaccine. The meme is a screenshot of a 14 February 2021 tweet by journalist Alex Berenson, who previously spread misinformation about public health measures during the COVID-19 pandemic.

The basis of the claim is a comparison between the number of deaths reported to the U.S. Vaccine Adverse Events Reporting System (VAERS) after receiving the COVID-19 and flu vaccines. Based on these reports, Berenson claimed that COVID-19 vaccines are associated with “one death per 35,000 shots or 10,000 complete vaccinations” compared to “one death per 9,000,000 vaccinations” in the case of flu. However, these numbers are inaccurate. As of 16 February 2021, the U.S. administered more than 55 million COVID-19 vaccine doses and 15 million full vaccinations. VAERS received 934 reports of death  following COVID-19 vaccination, which makes one reported death every 59,000 doses or 16,000 full vaccinations.

This comparison is also misleading readers into thinking that the vaccines caused these deaths. However, VAERS reports only tell us that an adverse event occurred after vaccination, without judging whether the vaccine caused it. Therefore, VAERS reports alone don’t demonstrate that one vaccine caused or contributed to an adverse event, as Health Feedback explained in this earlier review. For the same reason, these reports don’t allow us to compare the safety of different vaccines.

VAERS is a reporting system co-managed by the U.S. Centers for Disease Control and Prevention (CDC) and the U.S. Food and Drug Administration (FDA). The system collects information about adverse events occurring following vaccination, serving as “a national early warning system to detect possible safety problems in U.S.-licensed vaccines”. For that reason, VAERS encourages healthcare professionals and vaccine manufacturers to report any adverse events, regardless of whether they believe the vaccine caused them.

In addition, VAERS relies on individuals to report on any adverse event that occurs after vaccination, from mild side effects to serious adverse events. Since anyone can voluntarily report any adverse event, these reports may be subject to biases and contain information that is “incomplete, inaccurate, coincidental, or unverifiable”. Therefore, as the CDC explains, “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”.

While VAERS cannot prove if a vaccine caused an adverse event, they can help determine whether an adverse event requires further investigation. Safety monitoring indicates that COVID-19 vaccines are generally safe and effective and mostly cause mild side effects. Contrary to the claims that COVID-19 vaccines caused hundreds of deaths, none of the reported deaths has been attributed to the vaccine. The CDC and the FDA investigate any death report following COVID-19 vaccination to determine whether it was related to the vaccine. So far, CDC investigations found no evidence of a causal link between COVID-19 vaccines and any of the reported deaths:

“Over 52 million doses of COVID-19 vaccines were administered in the United States from December 14, 2020, through February 14, 2021. During this time, VAERS received 934 reports of death* (0.0018%) among people who received a COVID-19 vaccine. CDC and FDA physicians review each case report of death as soon as notified and CDC requests medical records to further assess reports. A review of available clinical information including death certificates, autopsy, and medical records findings revealed no link with vaccination. CDC and FDA will continue to investigate reports of adverse events, including deaths, reported to VAERS.”

In addition, the World Health Organization’s subcommittee for COVID-19 Vaccine Safety also found no association of the BioNTech/Pfizer vaccine with the deaths reported in Europe in very frail elderly populations:

“Reports are in line with the expected, all-cause mortality rates and causes of death in the sub-population of frail, elderly individuals, and the available information does not confirm a contributory role for the vaccine in the reported fatal events. In view of this, the committee considers that the benefit-risk balance of BNT162b2 remains favourable in the elderly, and does not suggest any revision, at present, to the recommendations around the safety of this vaccine.”

There is also no evidence that adverse events of COVID-19 vaccines are “widely underreported” compared with other vaccines. According to the CDC, COVID-19 vaccines have undergone the most intensive safety monitoring in U.S. history. In addition to surveillance through VAERS reporting, the CDC implemented a new smartphone-based tool called V-safe. This system uses “text messaging and web surveys to provide personalized health check-ins” and allows users to report any adverse effects following COVID-19 vaccination. Underreporting is often a problem in passive surveillance systems such as VAERS. However, increased awareness from media or other public information sources can also introduce a bias towards stimulated reporting[1].

Overall, VAERS is considered a highly efficient system for capturing vaccines’ severe adverse effects[1]. One example is the identification of rare cases of anaphylaxis in some people who had prior histories of allergic reactions. VAERS data allowed researchers to estimate the frequency of anaphylaxis in approximately two to five people per million vaccinated in the U.S.

In summary, VAERS reports only indicate that an adverse event occurred after vaccination. But the reports cannot demonstrate on their own that vaccinations caused or contributed to an adverse event or death. Evidence from clinical trials and continuous safety surveillance indicates that COVID-19 vaccines in use are safe. Further investigations of the reported deaths found no evidence that COVID-19 vaccines caused or contributed to them. Besides some rare cases of anaphylaxis, the data so far indicate that the vaccines don’t cause severe adverse events in the general population.


This explainer from Nature discussed in detail current knowledge about the side effects of COVID-19 vaccines, from common mild effects to rare cases of severe allergic reactions.


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