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. 

Conclusion

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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13 responses so far

13 Responses to “Vaccine Safety Systematic Review”

  1. jollyfischon 06 Jul 2014 at 5:48 pm

    Great article Steve.
    I recently came across an article in the New York Times, “The Price of Prevention: Vaccine Costs Are Soaring,” (6/2/2014) that addresses another barrier to vaccinations. All this hype about safety and effectiveness has led manufacturers to increase their prices in order to produce safer and more effective vaccines. Now many children are unvaccinated because they can’t find providers wiling to stock these expensive vaccines.
    How is it that the government can make vaccines mandatory but they can’t set price limits on them?

  2. evawes1on 07 Jul 2014 at 12:31 am

    Thanks for the great summary and conclusion Steven (even though this is familiar to regular readers). I have a few followup questions.

    I personally find a 1/1000 ratio fairly high. That is, I think one death from adverse effects out of a 1000 doses to be pretty high. I would need more information before stating that intervention is worthwhile. Is this a hypothetical ratio you are using as an example, or this is common? The 1.5/100000 (for RotaTeq) and 5.1/100000 (for Rotarix) is more palatable for me. This might just be my personal values.

    Is it usual practice to evaluate this AE ratio against the likely deaths from not vaccinating? For example, if 10/1000 people would die without vaccination; and then after vaccination 1/1000 died from vaccine adverse effects and the remaining 9 people lived, then I would say this pretty much supports vaccination.

  3. evawes1on 07 Jul 2014 at 12:35 am

    I think I may have misread the numbers you used. Re-reading it, I think you use an example of a vaccine saving 1000 lives (that otherise would have died from withour vaccinatino) but the adverse effects from the vaccine lead to one death. (For some reason I read 1000 doses and 1 AE). Thats fairly straight forward, and supports using vaccines. Although I would support further research to reduce adverse effects.

  4. SteveAon 07 Jul 2014 at 7:21 am

    I think some parents suffer from a ‘no blood on my hands’ mentality.

    They would rather take the passive chance that blind fate might cause their child injury, rather than make a positive decision to vaccinate, even if the risk of harm in doing the latter is far less.

  5. The Other John Mcon 07 Jul 2014 at 7:36 am

    SteveA – agreed. We see the same behavior in psychology of ethics. For the famous trolley problem, where a train trolley is barreling down the tracks and about to kill 5 people. Do you switch the tracks so that it kills only one innocent person on the other set of tracks? If the one person is a relative or significant other, people are much less likely to say they would throw the switch (they would let 5 die). The psychology is just like you said, where a positive action results in a (possible) single death, especially of a loved one, people prefer to remain passive despite its (possible) harm to many others.

    I believe this is also why, for death sentences, humans have generally arranged things so that whoever “throws the switch” or for firing squads, its setup so that no one single executioner can be seen to be the one definite cause of the death. I don’t know if this is always true, probably differs by state and country and such, but its true enough to merit this observation generally.

  6. The Other John Mcon 07 Jul 2014 at 7:46 am

    For those interested:

    Link to Trolley Problem:
    http://en.wikipedia.org/wiki/Trolley_problem

    Link about executions and the ‘diffusion of responsibility’: http://www.nytimes.com/2006/02/08/health/08iht-snmoral.html?_r=0

  7. mumadaddon 07 Jul 2014 at 7:55 am

    Other John,

    My understanding of the trolley problem was that the overwhelming majority will switch the track if it’s just a case of pulling a lever, although I’ve never heard of the example where the single victim is a loved one, which obviously changes things considerably.

    The other hypothetical situation I’ve always heard is that instead of simply pulling a lever, you can push a fat guy off a bridge, which will save the five but kill the fat guy. Same net result, but in this scenario most people will not push the fat guy off the bridge. The reason cited is that the second scenario involves emotion centres in the brain in the decision making process whereas the first does not.

  8. mumadaddon 07 Jul 2014 at 7:56 am

    Sorry I should add – the fat guy lands on the tracks, thereby stopping the trolley.

  9. The Other John Mcon 07 Jul 2014 at 12:25 pm

    Yes mumadadd you are correct, the majority will typically do a cold/rational utilitarian calculation and save 5 strangers while killing one, if it just involves throwing a switch. But having the one killed instead be a loved one, not a stranger, changes things dramatically. And yes, the more and more “active” or even seemingly barbaric things we ask people to do (push a fat man, shoot someone, etc.), even if it will only take 1 life while saving 5 others, keeps changing the calculations. We are only utilitarian in regards to strangers and when no active/brutal killing is required, but with friends or family, our emotional centers –wired by evolution–get involved and heavily favor our kin over others.

  10. DevoutCatalyston 07 Jul 2014 at 12:36 pm

    What a strange fat man who wouldn’t strongly resist or grab and throw you off the bridge and onto the tracks.

  11. SteveAon 08 Jul 2014 at 9:46 am

    DevoutCatalyston: “What a strange fat man who wouldn’t strongly resist or grab and throw you off the bridge and onto the tracks.”

    I’ve often thought the same myself.

    Also, what if the same voice is whispering in the fat man’s ear? ‘Throw him/her off the bridge and save five lives.’

    I wonder if, at some level, the risk of personal injury increase someone’s reluctance to throw fatty on the tracks.

  12. The Other John Mcon 08 Jul 2014 at 10:31 am

    Great question, if we imagine that we are supposed to “push” some large burly muscly man onto the tracks, are we less likely? I dunno, especially in comparison to some sweet old lady, who would be easy to push but easier to hug. Not sure what the literature says on this, haven’t been super-deep into it.

  13. DevoutCatalyston 08 Jul 2014 at 10:53 am

    I’m nitpicking, but how would a fat man stop a trolley ? I couldn’t quickly find a video of a trolley hitting something heavy, but watch what happens when a truck hits a trolley car (at about 24 seconds into this video),

    http://www.youtube.com/watch?v=3SfMhIS7RJ0

    Fat man vs. trolley car = beef cutlets. In the real world the trolley would continue onward and the would be savior just killed one person and didn’t do squat for any of the others. Chump.

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