Mailbag: Real Vaccine Risks?


It is time for another entry in the mailbag series where I answer feedback email from readers and others. If you want to send me a question, comment or any other kind of feedback, please do so using the contact form on the about page.

Nothing in the world is 100% safe or 100% effective. Everything you do carries some degree of risk: you can get hit by a car at a pedestrian crossing, choke when drinking water, accidentally fall when walking on gravel and so on. The challenge is to figure out if the benefits of something outweigh the risks, and if that is the case, then the product is reasonably safe and effective. It the risks clearly outweigh the benefits, the product is unsafe or ineffective.

These challenges are given substantial attention in the research and development of all medical products and certainly vaccines. This is due to several reasons: a dangerous product would be unlikely to pass the stringent regulatory checks and safeguards, a dangerous vaccine would just be pulled of the market, there is a very small profit margin for vaccines compared with other products (since most vaccines are only given once or a couple of times during life compared with other products that need to be taken every day) etc.

There are real risks with vaccines (as with any medical product), but these are either mild or very, very rare. However, what greatly irritates scientists, medical doctors and scientific skeptics is that anti-vaccine activists make up imaginary risks that are either enormously scientifically implausible (that smallpox vaccines turned people into cows) or have been repeatedly refuted by a massive amount of scientific research (such as most modern anti-vaccine claim).

Barzini wrote in and asked the following questions:

Do you agree that vaccines do sometimes cause severe harm in children? Or is your position that they never cause severe harm?

Yes, there are some very, very rare risks with vaccines. For instance, the MMR vaccine has a 1 in 1 million risk of a life-threatening allergic reaction. To further reduce this risk, medical personnel often ask about allergic reactions to any of the components of the MMR vaccine. Any rarer potential side-effects than this are extremely hard to detect and often indistinguishable from the background incidence.

Two great resources for vaccine side-effect is the two CDC documents on Possible Side-effects from Vaccines and Who Should NOT Get Vaccinated with these Vaccines? These documents provide high-quality and up-to-date information about real vaccine-side effects of each vaccine and contraindications about who should not receive a particular vaccine.

It seems clear to me that vaccines do sometimes cause severe harm, there are many testimonies from around the world of children reacting badly to vaccination (eg in car on way home from hospital), screaming for hours and hours, elevated temperature, and never being the same again from that day on.

Unfortunately, testimonials are unreliable as a guide to scientifically determining cause-and-effect. This is because humans cannot manage all possible exposures and confounders. So we need to look at scientific research. The alleged side-effects mentioned by Barzini is sustained screaming or crying, fever and presumably autism. Let us look at the CDC information.

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Checking the information for the DTaP vaccine, we can read that: “Non-stop crying, for 3 hours or more (up to about 1 child out of 1,000)”. So this means that about 0.1% of children may experience sustained crying from the DTaP vaccine. What about fevers? Looking at the CDC side-effect information reveal that fever is listed as a mild problem to several vaccines, with an incidence of about 1 in 3 to less than 1 in 100 (differing a bit depending on which vaccine). A mild fever is probably a small cost for the protection against dangerous vaccine-preventable diseases.

What about “never being the same again from that day on”? Well, there have been at least 13 high-quality studies with different research designs that have shown that there is no association between the MMR vaccine and autism and at least 7 studies that show no association between thimerosal and autism. These studies were reviewed in Gerber and Offit (2009). Two large-scale systematic review by the Institute of Medicine showed no association between vaccines and autism. The CDC also has a page on the myth that vaccines cause autism. They do not.

I’ve read statements from doctors saying that a very small percentage of children do sometimes react badly and that the reasons for this are currently unknown (ie more research is needed)

For the MMR vaccine, the reason is known: it is a severe allergic reaction.

However, let us skeptically unpack the method that is hinted at here. The first question we have to ask is: what doctors? Some doctors are cranks and some people pretend to be doctors, when they are, in fact, chiropractors, homeopaths, naturopaths and so on. Second, what are these statements and where were they found? A lot of proponents of pseudoscience often misquote real doctors out of context to make it appear as if they are saying something they are not. Third, how do the claims made by these doctors compare with the mainstream medical consensus position? It is not enough to reference “some doctors” without answering these questions.

If we accept that vaccines do sometimes cause harm, surely we should make parents aware of this risk (and the risk of not vaccinating of course), and then let them decide.

Parents are aware of these risks. They are explained by doctors, they are listed on vaccine package inserts and can be found on e. g. the CDC website. The problem is not that parents do not know the real side-effects of vaccines, but that they are being deceived by anti-vaccine activists on the Internet that claim side-effects that either is not supported by evidence, or has been directly disproved by research.

Barzini is also insinuating that vaccines are forced. This, however, is not true. There is a difference between mandatory vaccinations and compulsory vaccinations. If something is mandatory, you pay a societal cost from not doing it (your favorite school might require children to be up-to-date with their vaccines). If something is compulsory, the police will come to your house and make sure you do it. There is no compulsory vaccinations in the U. S. for children. To drive this point home, children with real medical contraindications do not have to be vaccinated as there are medical exemptions.

But the problem here is bigger. Let us apply the same logic that Barzini applies to vaccines to e. g. seat belts: “if we accept that seat belts sometimes cause harm, shouldn’t we let parents decide for themselves whether to use seat belts for their children?” This would be a batshit argument and everyone understands it. If you refuse to use a seat belt for your child (that is old enough for seat belts to work), then you are actively increasing the risk of serious harm or death for that child. It does not matter if you say that you drive well enough not to crash (“I keep my child isolated when there is a disease around”) or that you falsely claim that car crashes are beneficial (“natural immunity is better!”).

You are on the wrong side of medical science, on the wrong side of reality and on the wrong side of child safety.


Debunker of pseudoscience.


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