“Senator, I support vaccines. I support the childhood schedule. The only thing I want is good science, and that’s it.” These words were spoken by Robert F. Kennedy Jr during his confirmation hearing for Health and Human Services (HHS) secretary, addressed at Senator Elizabeth Warren who wasĚý.
The claim buried in this statement and in RFK Jr’s decades-long crusade against immunization—that there is no “good science” on vaccine safety—is bound to dominate public health discourse in the coming years, as Trump’s new administration has shown itself hostile to science and data. I heard it in person recently when someone who was clearly ill-informed told me we simply didn’t know how safe all these vaccines were.
As scientific knowledge gets stripped down by lies and public trust in life-saving technologies falls, it will be important to go back to basics and remind our neighbours how we know what we know. Vaccines are very safe and we know this because of a mountain of studies that have approached this question from multiple angles.
First off, vaccines do not arrive on the market with zero safety data. Following testing in animals, a new vaccine isĚýĚýin a small group of people (20 to 100), followed by another clinical trial in 100 to 300 people, followed by the largest trial in 1,000 to 3,000 people. These numbers are just guidelines: when Pfizer tested their COVID-19 vaccine, it was inĚýover 36,000 people. In the U.S., the Food and Drug Administration inspects the place where the vaccine will be manufactured, and vaccine lots are themselves tested for consistency. All of this information is considered by the committee deciding if the vaccine should be approved, and an approved vaccine must then be recommended, a decision made by yet another group.
This testing and evaluating, solid though it may be, is just the beginning.
CAEFISS and VAERS
Post-market surveillance means that even though a vaccine (or a drug) has been approved and is being used, we continue to study it. Clinical trials can only recruit so many participants, which means they will not pick up on rare side effects. That is where post-market surveillance comes in.
In Canada, theĚýĚý(CAEFISS) regularly publishes analyses of what happened after Canadians received a vaccine. This information comes from Canadians and their physicians choosing to fill out reports if something does happen, but CAEFISS also adds data from 12 paediatric hospitals that actively screen their admissions for such issues. We can look atĚýĚýscrutinizing the years 2018 and 2019, for example, and see that adverse events—meaning something bad that happened, which can include anything from a mild symptom like pain at the site of injection to death—were quite uncommon following vaccination: just under 11 such events for every 100,000 vaccine doses. Over 90% of these were not serious in nature; those that were serious were usually a seizure or a severe allergic reaction known as anaphylaxis. Nothing unexpected was seen during those years, nor was there any increase in their reporting compared to previous years.
In the U.S., monitoring is typically done using theĚýĚý(VAERS), but just like with CAEFISS,Ěýwe can’t simply scroll through the reports to sound the alarm.ĚýI cannot emphasize this enough. Adverse events being reported could simply be coincidences; they need to be compared to how common they normally are, and experts need to look for unusual symptoms which could indicate something new. Anti-vaccine activists are quick to extract scary-looking reports from the database in a move I have calledĚýthe VAERS scare tactic. The last time I checked, one report from a man who had just received a COVID-19 vaccine stated that his “penis swelled to ten times its size.” Using this report to claim that this vaccine will assuredly lead to either the greatest night of your life or to priapism would be grossly misleading.
There is so much data from post-market surveillance thatĚýĚýwas published by the Agency for Healthcare Research and Quality, one of the twelve agencies under HHS, on the safety of routine vaccination in the United States. Having looked at 189 such studies, the agency concluded there was no new evidence since their 2014 report of any increase in important adverse events following routine vaccination.
Scientists have not simply looked at the safety of all vaccines put together; they have also monitored the safety of individual vaccines, including those that have generated a lot of anxiety on the part of parents (often due to negative campaigns by anti-vaccine groups). Many people had qualms about the COVID-19 vaccines—especially those using mRNA to trigger an immune reaction—when they were rolled out, butĚýĚýlooking at the safety of the various COVID-19 vaccines within clinical trials concluded that there was “probably little or no difference between most vaccines and placebo for serious adverse events,” having looked at a total of 41 trials of 12 different COVID vaccines. Trials can’t pick up on extremely uncommon complications: sure enough, it was the data collected through post-market surveillance that allowed public health scientists to quickly spot a very rare but important complication of both the Oxford-AstraZeneca vaccine and the one made by Johnson & Johnson: blood clots. To say the COVID vaccines were not studied for safety would either be foolishly ignorant or a bald-faced lie.
Perhaps equally as controversial in the public eye, for a long while at least, was the MMR vaccine, an injection that included parts of the measles, mumps, and rubella viruses. TheĚýcause cĂ©lèbreĚýwas entirely manufactured: Andrew Wakefield, later stripped of his medical license, committed fraud by secretly accepting money from a lawyer who wanted to sue vaccine manufacturers and by faking data. His study was published inĚýThe LancetĚýin 1998 and finallyĚý. The public’s concern over a possible association between the MMR vaccine and autism was not simply cast aside by dismissive doctors; it wasĚýłŮłó´Ç°ů´ÇłÜ˛µłó±ô˛âĚýstudied.
Six years after the publication of Wakefield’s corrupt study, the Institute of Medicine releasedĚýĚýon the body of evidence investigating a link between autism and vaccines, particularly those containing a mercury derivative named thimerosal. In the Institute’s Vulcan-like scientific wording, it favoured “rejection of a causal relationship” between the MMR vaccine or any thimerosal-containing vaccine and autism, pointing out that the mechanisms by which thimerosal could cause autism were “theoretical only.” Basically, no good evidence to support the claim that these vaccines cause autism.
Denmark looked at over half a million children who had, in the 1990s, either received the MMR vaccine or not, findingĚý. Our own city of Montreal was scrutinized, with a team from 91ÉçÇř looking at over 27,000 children who attended English schools to look for a link:Ěý. Meanwhile, Japan became the focus of an interestingĚýde factoĚýexperiment. Due toĚýĚýover a number of reports of meningitis following the MMR vaccine, their MMR vaccination program was terminated in April 1993. Looking at the Japanese city of Yokohama, a team of scientists clearly saw that after MMR vaccination stopped, cases of autismĚýĚý(because, as we now know, of increased awareness and changes in the diagnostic criteria). It’s hard to argue that the MMR vaccine is what causes autism when yearly casesĚýincreaseĚýafter you stop using the vaccine. This is by no means a complete picture of all the studies that were done trying to find a link between thimerosal and autism and confirming that there was none, but it should be enough to show that multiple investigations were carried out.
The reason why thimerosal was present in some vaccines was because these vaccine bottles contain multiple doses. As sterile needles go in and out of these vials, there is a small risk that the content will become contaminated with bacteria or fungi that would then get injected into someone. Thimerosal acted as a preservative but it was completely removed from nearly all vaccines delivered in the U.S. inĚýĚýout of an abundance of precaution. (OnlyĚý˛ő´Çłľ±đĚýflu vaccines still contain thimerosal in theĚýĚýand inĚý.)
Vaccine ingredients, like thimerosal but also formaldehyde and aluminum, have often been accused of causing harm, but understanding dosing is key. Formaldehyde may be commonly used as embalming fluid, but our bodies need some formaldehyde to makeĚýĚý(via a molecule derived from formaldehyde calledĚý). It’s the dose that makes the poison. In their first two years of life, an infant could be exposed toĚýĚýof formaldehyde from vaccines. Meanwhile, a single apple contains in the neighbourhood of 1 to 5 mg of the substance (based onĚýĚýĚýsources). As for aluminum, it is one of the most common elements on earth, and the amount present in vaccines is overshadowed byĚý—including baby formula.
Common arguments
Even if someone accepts this stack of safety data and scientific knowledge, they could still argue the following: what if a vaccine causes problems 50 years down the road? How can we protect ourselves from this risk when clinical trials don’t run for decades? The short answer is that, despite claims to the contrary fomented by the anti-vaccine movement, we are not aware of vaccines suddenly causing damage decades after they have been injected. Moreover, allowing 2.6 million children to die every year—which is an estimate of how manyĚýĚýpre-vaccine—while we observe clinical trial participants for 50 years just in case something bad happens would be, I hope you can see, ethically precarious. We do not have the latitude to wait forever while significant percentages of our population are maimed and killed by infections.
Some will argue that vaccines have never been compared to placebos. As a blanket statement, it is categorically false. As I haveĚýwritten previously, plenty of vaccines were pitted against placebos (including injections of saline); but in some cases, the use of a placebo would mean creating an arguably unethical situation. If you wanted to test a new measles vaccine, the people in your placebo group would be prohibited from receiving the preexisting measles vaccine that the rest of the population is getting, thus putting them at increased risk for contracting the disease. Placebos are good but ethical considerations shouldn’t be ignored.
What about the argument that everyone involved in testing vaccines for safety is paid by the pharmaceutical industry and it is thus in their interest to hide evidence of harm? Conflicts of interest do exist, and there is a well-known and often-denounced revolving door between industry and regulation. But to claim thatĚýevery scientistĚýinvolved in vaccine research is corrupt? That millions of researchers, including those merely analyzing data from the past and comparing rates of autism between vaccinated and unvaccinated groups, are actively concealing dangers? We’re now in the realm of the grand conspiracy theory, for which there is no evidence. Vaccine researchers have families and children, too, and some even went into the field after witnessing the harms of vaccine-preventable diseases. To portray them as money-hungry automata doing the bidding of some shadowy cabal is simply irrational.
This being said, vaccines are not 100% safe. They often cause minor and temporary problems, like fatigue and fevers, and in rare cases they cause more serious damage. But we did not develop vaccines to serve as a fun Russian roulette; they exist to prevent widespread and debilitating harm. Measles, which is airborne and extremely contagious, causes swelling of the brain inĚý, and it can wipe your immunological memory for years, making you susceptible to infections you were previously protected from. Rubella causes birth defects. Polio can lead to permanent paralysis and the need for a portable ventilator to breathe. Risks are not only present with a medical intervention; they also exist in the diseases they are there to prevent.
I’ve recently referred to the contention that we don’t have any studies on something that has been thoroughly studied asĚýthe square one fallacy. It can be wielded by liars and easily adopted by an audience that does not know how much we already know. When it comes to vaccine safety, we are not starting from square one.
Moving forward, though, the American side of this system of knowledge is already being decimated by Elon Musk’s hirelings and by anti-vaxxer Robert F. Kennedy Jr. As was recently pointed out by virologist Angela Rasmussen onĚý, vaccine development and oversight require agencies like the NIH and FDA, and masses of employees at these entities have been carelessly fired in the last weeks.
If you wanted evidence that vaccines are unsafe, firing the people responsible for their safety would certainly create the very reality you spent decades imagining.Ěý
Take-home message:
- Some people claim that the safety of vaccines has never been adequately studied, which is false
- Vaccine safety is studied in a series of larger and larger clinical trials before they can be approved, and surveillance continues after a vaccine is used to monitor for rare side effects
- The alleged link between autism and vaccines (especially with the vaccine ingredient thimerosal) has been thoroughly investigated and it does not exist
