What is the evidence that an "anti-vaccination movement" is "causing" epidemics of childhood diseases in US? ("HFC! CYPHIMU?" Episode No. 2)
note: go ahead & read this but if you do you have to read this.
This is the second episode of “Hi, fellow citizen! Can you please help increase my understanding?”--or“HFC! CYPHIMU?"--a spinoff of CCP’s wildly popular feature, “WSMD? JA!.” In "HFC! CYPHIMU?," readers competete against one another, or collectively against our common enemy entropy, to answer a question or set of related questions relating to a risk or policy-relevant fact that admits of scientific inquiry. The questions might be ones that simply occur to me or ones that any of the 9 billion regular subscribers to this blog are curious about. The best answer, as determined by “Lil Hal,”™ a friendly, artificially intelligent robot being groomed for participation in the Loebner Prize competition, will win a “Citizen of the Liberal Republic of Science/I ♥ Popper!” t-shirt!
I'm simply perplexed here. What's the evidence to support the claim that public resistance to childhood vaccination is connected to an increased incidence of any childhood disease? Where do I find it?
If one does a Google search, one can easily find scores of alarming new sreports about "growing" anti-vaccine "movement" and its responsibility for outbreaks of diseases such as whooping cough.
But it's really really hard to find a news story that presents the sort of evidence that a curious and reasonable person might be interested in seeing in support of this genuinely scary assertion.
Look, I'm 100% positive that there are vocal, ill-informed opponents of childhood vaccination. Seth Mnookin paints a vivid, disturbing picture of them in his great book The Panic Virus. These groups assert that childhood vaccinations cause autism, a thoroughly discredited claim that has been shown to have originated in flawed (likely fraudulent) research.
If the question is whether we shoud condemn such folks, the answer is clearly yes.
But if the question is whether we should conclude that "[t]he anti-vaccine movement [has] cause[d] the worst epidemic of whooping cough in 70 years," etc., then we need more than the spectacle of such know-nothings to answer it. For such a claim to be warranted, there must be empirical evidence of (a) declining childhood vaccination rates that are (b) tied to disease epidemics.
Actually, it's pretty easy to find evidence-- outside of media reports on the anti-vaccine movement-- that tends to suggests (a) is false. Consider this table from a recent (Sept. 2012) Center for Disease Control Morbidity and Mortality Weekly Report:
What it shows is DTaP vaccination rates for pertussis (whooping cough) holding steady at 95% for 3 or more doses and about 85% for 4 or more over the period from 2007-2011.
For MMR (mumps, measles, rubella), the rate hovers around 92% for the entire period.
The rate of "children receiv[ing] no vaccinations" remains constant at about 0.7% (i.e., less than 1%). (In between these rows of data are rates for various other vaccinations -- like the one for Hepitatis B -- which all seem to show the same pattern. See for yourself.)
As for (b), it's also not too hard to find public health studies concluding that the outbreak in whooping cough was not caused by declining vaccination rates. One, published recently in the New England Journal of Medicine, found that the incidence of whooping cough was actually slightly higher among children who had received a full schedule of five DTaP shots than those who hadn't, and that their immunity decreased every year after the fifth shot. That's not what you'd expect to see if the increased incidence of this illness was a consequence of nonvaccination.
"So what are the causes of today's high prevalence of pertussis?," asked a opinion commentary writer in NEJM.
First, the timing of the initial resurgence of reported cases suggests that the main reason for it was actually increased awareness. What with the media attention on vaccine safety in the 1970s and 1980s, the studies of DTaP vaccine in the 1980s, and the efficacy trials of the 1990s comparing DTP vaccines with DTaP vaccines, literally hundreds of articles about pertussis were published. Although this information largely escaped physicians who care for adults, some pediatricians, public health officials, and the public became more aware of pertussis, and reporting therefore improved.
Moreover, during the past decade, polymerase-chain-reaction (PCR) assays have begun to be used for diagnosis, and a major contributor to the difference in the reported sizes of the 2005 and 2010 epidemics in California may well have been the more widespread use of PCR in 2010. Indeed, when serologic tests that require only a single serum sample and use methods with good specificity become more routinely available, we will see a substantial increase in the diagnosis of cases in adults.
In addition, of particular concern at present is the fact that DTaP vaccines [a newer vaccine introduced in the late 1990s] are less potent than DTP vaccines.4 Five studies done in the 1990s showed that DTP vaccines have greater efficacy than DTaP vaccines. Recent data from California also suggest waning of vaccine-induced immunity after the fifth dose of DTaP vaccine.5 Certainly the major epidemics in 2005, in 2010, and now in 2012 suggest that failure of the DTaP vaccine is a matter of serious concern.
Finally, we should consider the potential contribution of genetic changes in circulating strains of B. pertussis.4 It is clear that genetic changes have occurred over time in three B. pertussis antigens — pertussis toxin, pertactin, and fimbriae. . . .
Nothing about declining vaccination rates. Nothing.
The writer concludes, very sensibly, that "better vaccines are something that industry, the Center for Biologics Evaluation and Research of the Food and Drug Administration, and pertussis experts should begin working on immediately."
He also admonishes that "we should maintain some historical perspective on the renewed occurrences of epidemic pertussis and the fact that our current DTaP vaccines are not as good as the previous DTP vaccines: although some U.S. states have noted an incidence similar to that in the 1940s and 1950s, today's national incidence is about one twenty-third of what it was during an epidemic year in the 1930s."
I should point out too that in research I've done, I've just not found any evidence that a meaningful proportion of the general public views childhood vaccination as risky, or that there is any meaningful cultural divisions on this point.
Indeed, such vaccinations are one of the most commonly cited grounds members of the U.S. general public give for their (remarkably) high regard for scientists.
So ... what to make of this?
Here are some questions:
1. Is there evidence I'm overlooking that suggests there really is a meaningful, measureable decline in vaccine rates in the U.S.? If so, please point it out, and I will certainly post it!
2. Is there evidence that nonvaccination (aside, say, from that in newly arrived immigrant groups) is genuinely responsible for any increase in any childhood disease? Ditto!
3. If not, why does the media keep making this claim? Why do so many people not ask to see some evidence?
4. If there isn't evidence for the sorts of reports I'm describing, is it constructive to make people believe that nonvaccination is playing a bigger role than it actually is in any outbreaks of childhood diseases? Might doing so actually reduce proper attention to the actual causes of such outbreaks, including ineffective vaccines? Might they stir up anxiety by actually inducing people to believe that more people are worried about the vaccines than really are?
Can you please help increase my understanding, fellow citizens?
Some helpful commentators have sent things in offline. I will consult the rules committee on whether they are eligible to win the t-shirt.
Just to sharpen a bit:
1. I don’t dispute—and don’t see how any reasonable person could—that there will be a correlation between the vaccine rate and incidences of various diseases. For that reason, we should promote vaccination through mandatory vaccination regimes and other appropriate public health policies and should condemn anyone who denies these things. Good arguments and good evidence for these propositions are easy to find. But they are not what I'm asking about.
2. I’m interested in the claim—made over & over & over in words to this effect—that there is a "growing anti-vaccine movement, typified in coastal California's whooping cough outbreaks"? First, what does it mean for there to be a “movement”? Second, what is the evidence that it is “growing”? And third, what is the evidence that growth in the movement is influencing the incidence of childhood diseases?
One commentator referred me to:
Omer, S.B., Enger, K.S., Moulton, L.H., Halsey, N.A., Stokley, S. & Salmon, D.A. Geographic Clustering of Nonmedical Exemptions to School Immunization Requirements and Associations With Geographic Clustering of Pertussis. American Journal of Epidemiology 168, 1389-1396 (2008).
This study finds that there is a greater incidence of whooping cough in census tracts with higher numbers of “exempters.” I'd put this study in category 1. Nothing in it suggests that a “growing anti-vaccine movement” is “causing” an epidemic in whopping cough. Indeed, it addresses a period from 1993 to 2004—well before the outbreaks in 2010 and 2012. I assume the NEJM commentary writer was aware of this study when he concluded that an ineffective vaccine booster (the source of the outbreak identified in the NEJM study) combined with new strains of pertussis was the source of the outbreaks in 2010 and 2012. But in any case, it doesn’t support the assertion that the “Anti-Vaccine Movement Causes the Worst Whooping Cough Epidemic in 70 Years,” and doesn't make the argument for presenting the case for universal vaccination in these terms.
Maybe some other set of data do.