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Do not use VAERS to evaluate vaccine adverse events

Last updated on September 23rd, 2021 at 12:16 pm

The Vaccine Adverse Event Reporting System (VAERS) is one of the systems employed by the US Centers for Disease Control and Prevention (CDC) and the Food and Drug Administration (FDA) to monitor vaccine safety. VAERS is a post-marketing surveillance program, collecting information about adverse events (including death) that occur after the administration of vaccines to ascertain whether the risk-benefit ratio is high enough to justify the continued use of any particular vaccine.

VAERS, the Vaccine Safety Datalink (VSD), and the Clinical Immunization Safety Assessment Network (CISA) are the major tools used by the CDC and FDA to monitor vaccine safety. These are powerful tools that contradict the trope from anti-vaccine activists that regulatory agencies do not monitor vaccine safety – they do.

This article will review how VAERS works along with its strengths and limitations. However, one thing we will focus on how dumpster diving into the VAERS database without context is a very bad use of statistics.

Chen RT. Evaluation of vaccine safety after the events of 11 September 2001: role of cohort and case-control studies. Vaccine. 2004 May 7;22(15-16):2047-53. Review. PubMed PMID: 15121321.
From Chen RT. (see citation below)

Vaccine mortality – don’t use VAERS

Vaccine deniers, especially in the USA, love to use the passive data from the Vaccine Adverse Event Reporting System (VAERS), a system where individuals can report supposed adverse events post-vaccination, to “prove” certain adverse events. The reports can be made online, by fax, or by mail.

However, there are no investigations to show any type of causality between the vaccination event and the claimed mortality that are reported to the VAERS database, and, frankly, it can be gamed by those with nefarious intentions.

VAERS is a feel-good system for those who think that there’s a link between vaccines and something terrible, but without an active investigation, the data is just above the level of totally meaningless. Most epidemiologists know it is valueless. Even the VAERS system itself says that the data cannot be used to ascertain the difference between coincidence and true causality.

For example, there is a background rate for mortality, across all causes, irrespective of whether an individual is vaccinated or not, and unless you understand the background rate, the vaccine “mortality” rate has no scientific meaning. In fact, we could provide a Starbucks coffee drinking in the car “mortality rate”, which may or may not have any causality whatsoever.

However, and many vaccine supporters miss this point, the VAERS system can be used to provide observational data that could be used to form a testable hypothesis, the hallmark of real science. Using VAERS as evidence to support a hypothesis, for example, “vaccines cause people to die”, is pseudoscience, pure and simple.

On the other hand, we can use observational data that there appear to be more XYZ events after certain vaccines in the VAERS database to develop a hypothesis that “vaccines cause XYZ”, and thus becomes experimentally testable, usually through epidemiological data or in a clinical trial. At that point, we would either have evidence that supports the hypothesis or nullifies it. (Actually, that’s a false dichotomy, the experimental data may do neither, and further scientific studies are required.)

The Vaccine Safety Datalink (VSD) is a collaborative effort between CDC’s Immunization Safety Office and nine managed care organizations (MCOs) in the USA. The VSD was established in 1990 to monitor immunization safety and address the gaps in scientific knowledge about rare and serious events following immunization. 

The VSD includes a large linked database that uses administrative data sources at each MCO, most of which are high-quality, modern organizations that carefully track patients after immunizations. Each participating site gathers data on vaccination (vaccine type, date of vaccination, concurrent vaccinations), medical outcomes (outpatient visits, inpatient visits, urgent care visits), birth date, and census data. This data can be used to develop high-quality epidemiological evidence which can establish or refute causal links between vaccinations and various adverse events, including mortality.

In a study using the Vaccine Safety Datalink, investigators analyzed four years of data, between January 1, 2005, and December 31, 2008. and determined that background mortality rates (rates of death irrespective of cause) are crucial in interpreting the numbers of deaths following vaccination. Their major conclusion was that the VSD mortality rate following vaccination is actually lower than the general US population mortality rate, while the causes of death are similar.

In other words, if you look at the mortality rate post-vaccine in a passive system like VAERS, without the context of the general mortality rate, you might jump to an unsupported conclusion.

Lead investigator Natalie L. McCarthy, MPH, an epidemiologist at the Centers for Disease Control and Prevention (CDC) stated that:

Determining the baseline mortality rate in a vaccinated population is necessary to be able to identify any unusual increases in deaths following vaccine administration. VSD mortality rates demonstrate a healthy vaccinee effect where rates were lowest in the days immediately following vaccination, most apparent in the older age groups. The healthy vaccinee effect suggests an avoidance or delay of vaccination when an individual is sick, leading to lower background rates of illness or mortality immediately following vaccination.

Although there is currently no evidence to support a causal relationship between vaccinations and death, this study provides background mortality rates following vaccination to be used as a baseline when examining the safety profiles of new vaccines and during mass immunization campaigns.

The power of this study is significant. The study followed 13,033,274 people vaccinated with at least one vaccine, which included 17,108,478 vaccination visits with 24,842,470 total vaccines administered. This is not a small study. Here are some of the key results:

  • Among 13,033,274 vaccinated people, 15,455 deaths occurred within 60 days following vaccination.
  • The rates were highest in people of age 85 years and older, and increased over the period following vaccination.
  • Eleven of the 15 leading causes of death in the VSD and NCHS overlap in both systems, and the top four causes of death were the same in both systems.
  • Death on the day of vaccination was rare (132 out of the nearly 25 million vaccine doses, or less than 0.001%).
  • For children aged less than 1 month, the death patterns observed in VSD are consistent with National Center for Health Statistics (NCHS); most neonatal deaths occur within 24 hours after birth. This data refutes the myth that the HepB vaccination at birth has an effect on mortality.

In other words, there is no difference between the death rate and cause in the VSD and 2008 National Center for Health Statistics data. None.

The authors make this important conclusion:

The main finding from this study was the low mortality rates in the days immediately following vaccination, providing evidence of a healthy vaccinee effect. Although there is currently no evidence to support a causal relationship between vaccinations and death, this study provides background mortality rates following vaccination to be used as a baseline when examining the safety profiles of new vaccines, and during mass immunization campaigns.

Photo by Priscilla Du Preez on Unsplash


So this study has two important factors. It is, as a standalone study, shows that vaccinations don’t increase the mortality rate, and in some age groups, reduce it significantly. But it also can be used as a baseline against which we can compare the mortality rates in new vaccine studies (including clinical trials prior to regulatory approvals). This is good science. And vaccines save lives, and we can provide evidence for it.

With our current focus on COVID-19 vaccines, VAERS has become a battleground for misinformation about the vaccines’ safety. Even a recent anti-vaccine published article (since retracted) used a similar database in Europe to claim that “two people who receive the vaccine will die for every three lives saved.” It was a completely incompetent review of VAERS-like data to come to a conclusion that supports the anti-vaccine narrative rather than real science.

Despite the claims of the anti-vaccine crowd, VAERS is not the last word in determining whether vaccines cause adverse events. In fact, it tells us almost nothing about causality, that’s why the CDC and FDA employ better, more scientifically powerful tools, to determine if there is a causal relationship between a vaccine and a particular adverse effect.

VAERS can be used as a “safety signal” which may or may not turn out to be a real issue. For example, the relationship between COVID-19 mRNA vaccines and myocarditis appeared on VAERS first, but then the scientists at the CDC investigated whether there was a real link. Although the data is very weak, the CDC and FDA decided to give guidance to physicians just in case. That’s the proper way to use VAERS.

Earlier this year, Orac wrote about how anti-vaxxers will use VAERS to discredit the COVID-19 vaccine:

Indeed, antivaxxers have long loved to portray VAERS as the be-all and end-all of the databases monitoring vaccine safety. The reason, to reiterate, is that VAERS is unique among US vaccine safety reporting systems in that it is a passive surveillance system. It relies on people to submit reports of adverse reactions to vaccines; it doesn’t actively look for them, as active surveillance systems do. Moreover, anyone can submit a report to VAERS, and they do, including parents of autistic children seeking compensation for their children’s autism as being due to “vaccine injury”. Indeed, I long ago discussed how lawyers have long gamed VAERS to support their litigation, reporting lots of cases of autism as supposedly an “adverse reaction” to vaccines. It’s not just vaccines and autism, either. The easily-abused nature of VAERS data is one huge reason why those of us who’ve been following the antivaccine movement a long time like to refer to the bad “scientific studies” published by antivaccine physicians and scientists that use VAERS as their data source as “dumpster diving“.

But the worst thing that can be concluded from the VAERS data base is trying to tie vaccines to mortality, especially while ignoring mortality in the general population. What you’ll usually find when you do real investigation is that the mortality rate post vaccination is lower than the general population.

VAERS is a tool of varying quality. It should not be cherry-picked as if it is the final word on vaccine mortality or adverse events. That’s not science.



Michael Simpson
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