In Colorado, you are allowed to enroll your children in school without them having had all their supposedly required vaccines. Instead, Colorado parents are allowed to sign a waiver and then enroll their children. According to a KCFR/Colorado Public Radio interview with a medical researcher working for Kaiser Permanente, this fact partly explains why Colorado has about 800 cases of pertussis (aka whooping cough) a year, one of the highest rates in the country.

Kaiser Permanente (KP) is a large HMO that maintains its patient records in electronic form, a fact that makes the records very useful for researching disease. A new study performed by researcher Jason Glanz of KP finds that children who have never received a pertussis vaccine are 23x more likely to catch the disease than children who have been vaccinated. Of the approximately 800 cases of pertussis per year, that works out to 767 children who might not have caught pertussis if they’d been vaccinated, while only 33 children would have caught pertussis even after receiving the vaccine.

The interview suggests that one reason parents might be resistant to vaccinating their children is that all vaccines cary some small risk of severe reactions. Flu vaccine is produced in eggs, for example, and so a child with an undetected egg allergy could have a serious allergic reaction. Similarly, while vaccines no longer use mercury-based preservatives, such preservatives have been used in the past and parents understandably might not want to expose their children to mercury. The problem is that the vaccine risks are almost always lower than the risks of the disease being vaccinated against.

The risk of a severe reaction to pertussis vaccine is approximately 1 in 15,000. The Census Bureau estimates that there were 1.21 million children under the age of 17 in the state of Colorado in 2008. Those 767 children who weren’t vaccinated and still caught pertussis works out to a rate of unvaccinated pertussis of 1 in 1578, nearly 10x the rate of severe reactions. The rate of vaccinated pertussis is 1 case in 36,667.

In other words, your children are ten times more likely to get pertussis if they’re unvaccinated than they are to suffer from a severe vaccine reaction.

Ultimately, though, while the data is unequivical regarding the effectiveness of the pertussis vaccine, sometimes data just doesn’t matter. Sometimes it’s enough to know that a “severe” reaction could be as minor as a high fever or crying for several hours or as severe as convulsions. The human mind doesn’t always pay attention to the data, after all, focusing instead on the worst case. That approach has proven to be a good survival strategy, even if it’s misguided in this case. To parents who refuse to vaccinate their children, I have only one thing to say:

Talk to your pediatrician and follow their advice. And if your pediatrician has children and vaccinated them, well, that’s called “putting your money where your mouth is,” and it’s worthy of respect.

Ok, so I have two things. In case you’re wondering, I’ve had my children vaccinated.