One more time: Vaccine refusal endangers children

ResearchBlogging.orgOne of the claims of the anti-vaccine movement that most irks me is that their actions do not risk harm to anyone other than their own unvaccinated children. Given that vaccination against many infectious diseases also depends on the concept of herd immunity to provide protection to members of the population who either cannot be vaccinated for medical reasons, are too young to be vaccinated, or who belong to the minority who do not develop adequate immunity to vaccination, such claims are patently false. However, another frequently stated belief is that vaccines are ineffective, that they are not necessary to avoid the infectious diseases they protect against. They seem to think that good nutrition and good living will be enough. It’s not, of course, but that’s what they think.

Today a study was released in the June 1 issue of Pediatrics that demonstrates just that. A collaborative effort between the University of Colorado, Kaiser Permanente Colorado (KPCO), Johns Hopkins Bloomberg School of Public Health, and Community Health Services, Denver, it’s entitled Parental Refusal of Pertussis Vaccination Is Associated With an Increased Risk of Pertussis Infection in Children. It’s shown up in the media, including NPR, under titles such as Is Vaccine Refusal Worth The Risk?, Unvaccinated kids 23 times as likely to get pertussis, Kaiser study shows, and Whooping cough returns in kids as parents skip vaccines. Its conclusions are the kind of “well, duh!” conclusions that are painfully obvious. Unfortunately, the anti-vaccine movement has been successful enough in bringing back once rare or even virtually eradicated diseases back to threaten our children that studies of this sort do need to be done.

Colorado, unfortunately, is the perfect place to do a study of this sort. Boulder, CO has been one of the strongholds of the anti-vaccine movement for quite some time, as described in 2002 by Arthur Allen:

Boulder, which has the lowest schoolwide vaccination rate in Colorado, has one of the highest per capita rates of whooping cough in the United States. The problem started in 1993 when fifty-two people in Boulder County contracted the disease. Since then the county has seen an average of eighty-one cases a year. Although unvaccinated children are six times as likely as vaccinated children to get whooping cough during an outbreak, about half the cases in Colorado have involved vaccinated children; the whooping cough vaccine sometimes fails to produce effective immunity, and even successful pertussis immunity generally wanes by age ten. “At first we called it an outbreak, then we started calling it a sustained outbreak; now we just say it’s endemic,” Ann Marie Bailey, the county nurse epidemiologist when I visited Boulder last year, told me.

Glantz et al took advantage of this and Kaiser Permanente’s extensive database of patients in Colorado to perform a case control study of children enrolled in Kaiser Permanente between 1996 and 2007, determining vaccination status and pertusis status by chart review. Kaiser in Colorado has 430,000 current members, and children receive full vaccination coverage as recommended by the Advisory Committee on Immunization Practices. The study was designed to determine if children who contracted pertussis infection were more likely to have parents who refused pertussis vaccinations than a similar group of children who did not develop pertussis infection. All potential cases of pediatric pertussis were identified using KPCO’s database, and skilled medical abstractors, who were blinded to the vaccination status of the research subjects, examined the charts to identify which children carried a diagnosis of pertusis. Patients were classified as confirmed cases if they had a medical chart-verified positive PCR test or a positive culture for Bordetella pertussis, the bacteria that causes pertusis. Controls without for each case of pertusis were four randomly selected children controls matched by gender, length of KPCO enrollment, and age at the date of diagnosis. Vaccination status was then determined for each group, and parents were classified as “vaccine refusers” if they had refused one or more vaccines for nonmedical reasons.

The results? Glantz et al identified 156 laboratory-confirmed pertussis cases and 595 matched controls The relative risks of pertussis among vaccine refusers and matched controls are summarized in the chart below:


The results are striking. Vaccine refusal is associated with a nearly 23-fold increased risk of developing pertussis. Indeed, it’s even more than that. In the vaccine refuseniks:

The percentage attributable risk in the vaccine refuser population was 99.5% (95% CI: 98.1%-99.9%), and the total population attributable risk was 11.0% (95% CI: 5.8%-16.0%). These estimates suggest that all 18 of the unvaccinated pertussis cases were attributed to vaccine refusal, and 11% of the pertussis cases in the total population were associated with vaccine refusal.

In other words, virtually all the risk of pertussis in the vaccine refusers came from being unvaccinated, and 11% of the pertussis cases in the total population can be attributed to vaccine refusal. One can only predict that that 11% figure will increase if vaccine refusal increases, thanks to the misguided and profoundly harmful campaign being waged by Generation Rescue, Jenny McCarthy, and other antivaccine activists, given that the only reason the number is that low now is because the vaccine is not 100% effective and the number of unvaccinated, although growing in many parts of the country, is still relatively small. In any case, what’s remarkable about this study is that it is the very first to use detailed individual-level data from well-maintained and detailed databases; previous studies have relied upon population-level data and school data. Those studies showed a six- or seven-fold increased risk associated with vaccine refusal, which is bad enough. This study, on the other hand, showed a higher risk probably because of more detailed, individual-level data, plus the fact that previous studies have shown that a significant proportion of children classified as vaccine exempt by schools may have actually been at least partially immunized. More importantly, though, school records don’t usually specify which immunizations were refused by parents when they claim a personal exemption. It’s impossible to know how many of those claiming exemptions actually did receive the DPT vaccine, which would tend to falsely depress the apparent relative risk of pertussis in the unvaccinated. This study pinpointed exactly which patients had refused the pertussis vaccine, allowing for a more accurate risk assessment.

The authors also tried to control for confounders. The most obvious confounder is obvious. Vaccine refusers often exhibit different health care choices and health care-seeking behavior when their children become ill. Specifically, they may be less likely to seek out “conventional” medical care when their children develop a cough or early symptoms that may be pertusis. Second, a child’s vaccination status, if known, can definitely influence how likely a physician is, when faced with a child with a severe cough, to test for pertussis. However, these two confounders would tend to act in different directions, with decreased visits to physicians tending to make a diagnosis of pertussis less likely for mild cases and the tendency of physicians to be more aggressive testing children who are unvaccinated tending to increase the likelihood of a pertussis diagnosis, especially in milder cases. The bottom line is that the net effect of these confounders was almost certainly small compared to the high relative risk found.

The authors conclude:

Despite high pertussis immunization rates in Colorado, herd immunity did not prevent a high relative-risk for pertussis in vaccine refusers. This is likely because of a combination of waning immunity to pertussis in adolescents and adults, ongoing endemic circulation, the highly contagious nature of the bacterium, and frequent asymptomatic infections. Of note, herd immunity to pertussis may increase over time because of the impact of the newly recommended adolescent and adult pertussis booster vaccines.


These results have important implications for families and the physicians who care for them. We found that children of parents who refuse pertussis vaccination are at a greatly increased risk for pertussis infection. This result dispels one of the commonly held beliefs among vaccine-refusing parents that their children are not at risk for vaccine-preventable diseases. Future research should focus on the community impact of vaccine refusal and the risks to other vulnerable populations, including children who are too young to be fully immunized and older adults with waning immunity. Furthermore, our study highlights the need for effective risk communication between parents and physicians about vaccines and the diseases they prevent.

I agree that effective risk communication is important. Indeed, fence-sitters may be convinced by hard data showing that failing to immunize does result in potentially seriously harmful consequences for their children. In that, this study might well help. However, I doubt that this study will sway anyone in the anti-vaccine movement. Showing them evidence, such as this study provides, that the risks of not vaccinating are real and potentially serious isn’t the issue. The real issue that drives them is on the vaccine risk side of the equation. The anti-vaccine movement has systematically exaggerated the risks of vaccination, spreading misinformation that they contain all sorts of “toxins” and repeating the scientifically discredited hypothesis that vaccines cause autism and various neurodevelopmental disorders. They don’t, but that is the real side of the equation that is driving the fear of vaccines. As Arthur Allen described in Boulder:

Jia Gottlieb, a family practitioner who offers acupuncture and breathing exercises along with traditional medicine, said, “When I get parents who don’t vaccinate, I tell them, ‘When your boy gets a vaccination he takes on a risk for the public good, just like the firemen [at the World Trade Center] who went back into the buildings.'” But Gottlieb’s words usually tall on deaf ears. “These are probably people who donate a lot of money to good causes,” he said, “but their view is ‘I’m going to let everyone else’s child take a risk but not my own.’ That’s not avant-garde. That’s not enlightened. It’s pretty primitive. And ironically, in a town like Boulder the selfish strategy is probably not in the best interests of your child either.'”

Indeed it’s not. Moreover, the example Gottleib uses is vastly overblown, as it equates vaccines with death in a burning building. That’s the very problem with the antivaccine movement; it vastly inflates the risk of vaccines beyond all reason. Indeed, it’s true that there is a small risk being taken on for the public good, but it’s infitessimally small on the order of one or two in a million for serious side effects, nowhere near akin to firemen running back into the World Trade Center on 9/11, where they faced a very high risk of death and knew it. Moreover, it’s about more than risking oneself to save others. That’s an important consideration, but vaccination has always been far more about protecting one’s children from serious diseases at a very low risk to those children compared to that of the diseases being protected against. Ironically, this study in Pediatrics is strong evidence that the “enlightened self-interest” shown by parents of vaccine refusers is not only not particularly enlightened but, when you come right down to it, not even truly in the self-interest of the children of antivaccine parents. Unfortunately, that message won’t sink into some thick skulls, as one burningly stupid comment after this story demonstrates so painfully:

Those of us who do not vaccinate our kids do not “refuse” to do so. We make an informed decisions. What the article doesn’t say is that those of us who choose not to risk vaccinations, have a far less likely chance of seeing side effects from the vaccine such as high fever, days of discomfort, and even long-term brain damage. There is a risk. There is always the risk. The important question is whether the risk is worth the benefit.

In the case of most vaccines, including pertussis, the answer is no.

Pertussis is not a dangerous disease when compared to the risks of vaccine. The chances of dying or long-term health risk is greater than the chance of serious side-effect from the shot. To be clear, you have as much or greater chance of getting sick from the shot then you do from the disease.

My kids both had whopping cough last summer. They were very sick for about a week or so, the cough continued for 10 weeks on and off and now I don’t have to worry about them getting it again because they are naturally immune. Not real serious.

This is the most typical situation.

Serious illness for a week, followed by a lesser degree of illness for ten weeks, and this idiot thinks it’ “not real serious.” Maybe if one of her children had died of whooping cough, which most definitely can happen, this woman would still consider it “not that serious.” I don’t know about you, but I’d have hated to have a mother so callous about my suffering as this mother, who is saying in essence to her children: “Don’t mind that week of coughing that’s making your chest hurt so much that it feels like your lungs are going to come bursting out of your throat and the ten weeks after that of still more coughing. Just think of the fantastic natural immunity you’ll have after all that suffering is over! After all, that which does not kill you makes you stronger.” In the meantime, look for the antivaccine propagandists at Age of Autism to attack this study within the next day or two, using the same sorts of callous and scientifically ignorant arguments as this mother. Despite the appeals to the “mommy instinct” that anti-vaccine spokeswomen like Jenny McCarthy like to make, the “mommy instinct” is often wrong, and good intentions do not always result in good outcomes. In fact, there’s a reason for the saying “the road to hell is paved with good intentions.”

As I mentioned at the beginning of this post, qualitatively, its conclusions are the kind of “well, duh!” conclusions that are painfully obvious and completely expected. Even so, I was surprised at the magnitude of the increased risk observed in the children of vaccine refusers; it was at least twice as much as I would have guessed if you had asked me before the study came out. To put it in perspective, the relative of lung cancer in heavy smokers is only on the order of 10 or so. Since certain a certain pediatrician who is an apologist for the anti-vaccine movement likes to make specious comparisons betwee the vaccine industry and the tobacco industry, I can’t resist finishing with this analogy. Unvaccinated children are at a such a high risk of pertussis compared to vaccinated children that this increased risk is more than twice the increase in risk that smokers have of getting lung cancer compared to nonsmokers.

Vaccine refusal is to infectious disease as smoking is to lung cancer, only twice as much!


Jason M. Glanz, PhD, David L. McClure, PhD, David J. Magid, MD, MPH, Matthew F. Daley, MD, Eric K. France, MD, MSPH, Daniel A. Salmon, PhD, MPH, & Simon J. Hambidge, MD, PhD (2009). Parental Refusal of Pertussis Vaccination Is Associated With an Increased Risk of Pertussis Infection in Children Pediatrics, 123 (6), 1446-1451