Pertussis is a highly contagious and potentially deadly respiratory infection that affects mostly children in the developing world. The low prevalence of pertussis in industrialized nations is partly due to the effectiveness of the pertussis vaccine. However, several studies have indicated that the rates of pertussis in the US have significantly increased during the last decade, likely due to a parallel decrease in vaccinations, as parents have become increasingly worried about vaccine safety. But is this true? Are children of parents who decline the pertussis vaccine at higher risk for acquiring this disease?
The journal of the American Academy of Pediatrics recently published a study that examined the association between vaccination refusal and pertussis infections in Colorado. In this study, the authors conducted a case-control examination of children between 2 months and 18 years who were members of a large health plan (Kaiser Permanente Colorado). The study included 156 cases of pertussis and 595 control non-pertussis children.
The authors found time trend in the cases of pertussis, with a large increase in cases of pertussis after the year 2000.
Of the 156 children who acquired pertussis, 12% were children of parents who refused vaccination.
In contrast, only 0.5% of the children who did not get pertussis were children of parents who refused vaccination.
Among children of all ages, refusing vaccination increased the risk of pertussis infection by 2,280%!!!
And these numbers may actually be an underestimate of the real risk of vaccine refusal, since the authors found a possible bias in diagnostic practices. Specifically, parents who agreed to vaccinate their children were 2 times more likely than vaccine-refusing parents to visit the doctor for upper respiratory infections. One interpretation of this finding is that parents who accepted the vaccination are more likely to seek medical services when their kids are sick than parents who refused vaccination. If this is the case, it is likely that cases of pertussis in the unvaccinated kids may have been missed (as these kids were less likely to visit the doctor) so that the rate of pertussis among unvaccinated kids is actually higher than what was observed in this study.
In sum, this study indicated that children of parents who refused vaccination were over-represented among cases of pertussis in Colorado during the past decade and that vaccination refusal increased the risk of pertussis by more than 2000%
These findings made me think about the underlying reasons that drive some parents to refuse vaccination: the fear that by vaccinating their kids they are increasing their kids’ risk of having a severe side effect. But I’m wondering if these parents are properly weighting the risks. Specifically, I wonder how many of these parents have reliable information about both sides of the equation; so that the real and known risks of vaccination are properly weighted against the real and known risks of non-vaccination (such as a 2,000% increase in the risk of acquiring pertussis)?
Glanz, J., McClure, D., Magid, D., Daley, M., France, E., Salmon, D., & Hambidge, S. (2009). Parental Refusal of Pertussis Vaccination Is Associated With an Increased Risk of Pertussis Infection in Children PEDIATRICS, 123 (6), 1446-1451 DOI: 10.1542/peds.2008-2150