I had the pleasure of speaking in the plenary session at the 2014 AAVLD/USAHA Annual Meeting this week, where, among other topics, we discussed risk. One of the other panelists made the best point that I’ve heard in a long time – activists hate denominators.Think about the last few scare stories you’ve seen – there’s no doubt that it is frightening to read that 3,000 people die from food poisoning each year, or that, to date, 4,546 people have died from Ebola (one in the USA). Yet if we put this into context, one person out of 315 million in the USA dying from Ebola is a tiny tiny fraction, and a correspondingly tiny risk.
Activists hate denominators because they provide us with context, a way to assess whether we’re really in danger. Statistically speaking, you’re more likely to die from a traffic accident (one in 71 deaths), flu (one in 1,642 deaths), or syphilis (one in 55,866 deaths) than Ebola (one in 2,515,458 deaths). Which brings me to my current favorite activist, anti-vaccine zealot and proponent of “well-researched” bad science, Modern Alternative Mama (MAM). Thus week, she’s been promoting what she optimistically calls a “risk:benefit analysis” of the DTaP (diphtheria, tetanus and pertussis) vaccine.
Interestingly, she appears to consider all vaccine risks equal: death is no more of a minor inconvenience than redness at an injection site, and she earnestly notes that there is “no known benefit to getting diphtheria“. That sentence alone causes the mind to boggle. On a positive note, she does use valid CDC data, reporting that there were 3,169 adverse effects attributed to DTaP in 2011, which she claims is an underestimate of up to 9-fold.
So let’s run the numbers. Each year, approximately 3.95 million babies are born, of which 82.5% are given the DTaP vaccine. Between birth and 6 years of age, 5 doses of DTaP are recommended, so each year, 5 x 3.95 million x 82.5% = 16,293,750 doses are given (note that babies will have three each in that year, but older children (18 months and 4-6 years) will also receive a dose). Let’s give MAM the benefit of the doubt and assume adverse vaccine events are actually 5x the cited CDC number, at 15,845 events. The CDC classifies 10% of these events as “serious”, which equals 1,585 serious events per year.
So what is your child’s chance of having a serious reaction to the DTaP vaccine? 1,585/16,293,750 = 0.0000973, or one in 10,277 children will have a serious reaction to DTaP.
By contrast, we could take our chances in not vaccinating and hope that our child doesn’t contract diphtheria, which carries a risk of death of up to 20% in children under five years old. That means one in five children who contract diphtheria will die.
Given MAM’s antagonism towards vaccines, it’s not altogether surprising that she concludes “Although diphtheria is serious, it appears that the risk from the vaccine is much greater.” Yet let’s be realistic about this. One in 10,277 children will have a serious reaction to DTaP (serious reactions does not mean death, although that is one possible outcome) versus one in five children who will die after contracting diphtheria.
Admittedly that’s assuming that all unvaccinated children will get diphtheria. They won’t, but even if only 5% do, the risk is still overwhelmingly lower in the vaccine category (one in 10,277 suffering a serious reaction to the vaccine vs. one in 100 dying from diphtheria).
The site carries a disclaimer that writers are neither education professionals nor providing medical advice, yet the suggestion (by the author herself) that this is a well-researched, scientific post will no doubt cause some parents to congratulate themselves on their choice to not vaccinate.
This pseudoscientific scaremongering is dangerous, potentially lethal. All parents are concerned for their children’s health and welfare, but propounding nonsensical “risk:benefit analyses” that do not consider the denominator but simply the total adverse effects does not allow any parent to make a rational and well-considered decision. If my child is the one in 10,277 who suffers a serious DTaP vaccine reaction, I’m unlikely to care whether she is one of few or many, but at least I can make the decision whether or not to vaccinate (my answer is an overwhelming “yes”) based on risk. We all want our babies to grow up healthy and happy – in this case, it’s time to be a mainstream vaccinating Mama, rather than a “modern alternative” one.
Bovidiva 
Great post. I agree with your general point. Just having a little trouble w/ your 1 in 10,2777 risk. I thought it might be a typo, but it appears as such every time the number is referenced. Might want to clean that up if your bashing someone for their creativity with numbers… 🙂
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My bad – typed it wrongly the first time and then pasted the rest! Have corrected but thank you for alerting me! 🙂 It’s always the ironic typos that are the worst.
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Anti-vaccinationists are very dangerous. They’ve been steadily chipping away at vaccine rates over the last 10 years with their lies and idiocy. Sadly it will take the return of deaths from vaccine-preventable diseases to reverse this trend.
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I agree. Measles cases have reached a 20-year high (http://www.cdc.gov/media/releases/2014/p0529-measles.html) – when will this sink in as a significant issue?
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Anti-vaccine “activists hate denominators.’ I am so stealing that. Excellent article.
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It was the best quote of the entire day at the conference!
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