Jul 03 2014

Vaccine Safety Systematic Review

A new systematic review of adverse events from vaccines used in the US was recently published in the journal Pediatrics: Safety of Vaccines Used for Routine Immunization of US Children: A Systematic Review. (Full text pdf) This systematic review is actually an update and expansion to the 2011 Institute of Medicine (IOM) report on vaccine side effects.

The review looked at the best evidence available, active surveillance studies with controls, identifying 67 relevant studies. Overall they found that vaccines were very safe. There were a few associations with serious adverse events, but these were all very rare. From their conclusions:

Our findings may allay some patient, caregiver, and health care provider concerns. Strength of evidence is high that MMR vaccine is not associated with the onset of autism in children; this conclusion supports findings of all previous reviews on the topic. There is also high-strength evidence that MMR, DTaP, Td, Hib, and hepatitis B vaccines are not associated with childhood leukemia.

Evidence was found for an association of several serious AEs with vaccines; however, these events were extremely rare: absolute risk is low. For example, strength of evidence is moderate for association of vaccines against rotavirus with intussusception. Although 1 large US epidemiologic study found no association, a recent analysis of the US PRISM program found both RotaTeq and Rotarix associated with intussusception in the short term. Estimated rates were 1.1 to 1.5 cases per 100 000 doses of RotaTeq and 5.1 cases per 100 000 doses of Rotarix.

So a few vaccines are associated with rare AEs. Given the rhetoric of the anti-vaccine movement, there are a few points worth emphasizing here.

The first is that evaluations of medical interventions are based upon risk vs benefit – how much benefit are you buying with how much risk? If you focus exclusively either only on risk or only on benefit, you will not be seeing the whole picture and this is not sufficient to make a rational informed decision.

Anti-vaccine fearmongering tends to focus only on risk. For example, one anti-vaccine site states:

The idea of leaving your children unvaccinated makes much more sense when you understand the risks of vaccine side effects.

This is an invitation to consider only vaccine side effects. Whether you take a public health or an individual perspective, risk vs benefit is the only approach that “makes sense.” If an intervention saves 1,000 lives but one person will die of a serious AE, that ratio favors the intervention. This also means that for an individual, it is in your best interest to take the intervention, as it will decrease your chances of dying.

When all the data regarding vaccines are considered, they benefit the individual and the community. In fact, vaccines have one of the highest benefit to risk ratios of any medical intervention. It just doesn’t get much better than vaccines.

Anti-vaxers will often say that they are “pro-safe vaccine,” meaning (and often explicitly stated) that they want vaccines with zero risk. There is no such thing as a medical intervention with zero risk. Saying that only an impossible vaccine is acceptable is being anti-vaccine.

They also often state, in breathless terms, that vaccines do have side effects, as if the medical establishment pretends that they don’t. This review, as well as many other publications, and the information provided by the CDC and other medical institutions, clearly demonstrates that this is not true. We are completely open about the risks of vaccines. No one tries to hide this fact, only to put it into the perspective of risk vs benefit. 


Vaccines remain one of the most successful, cost effective public health interventions devised, with an extremely high benefit to risk ratio. This latest systematic review confirms the low overall risk of vaccines. It also supports prior reviews concluding that the MMR vaccine is not associated with the risk of autism.

The conclusion that vaccines are safe and effective is not controversial. It is a robust scientific conclusion, sufficient to convince the vast majority of medical professionals.

The anti-vaccine movement is at its core a denialist movement, whose product is fear and doubt. They distort the evidence, distort the standard logic of medicine, and when all else fails, they cry conspiracy. In fact, the conspiracy mindset is so embedded in the anti-vaccine culture, that they accuse anyone who disagrees with them of being a pharma shill as a knee-jerk response.

I am routinely asked (rhetorically) where I get my funding, or am explicitly accused of shilling for Big Pharma. It’s as if they cannot conceive that an independent professional (yes, for the record, again, I get no funding from anywhere except membership support, and have no connections to pharmaceutical companies or any other interests) will look at the data and come to a conclusion that differs from their propaganda.

They try to focus the discussion on imaginary conspiracies because when you focus on the evidence, there is only one conclusion that is supported – vaccines are safe and effective.

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