News sources are reporting a story about the terrific consequences of parents’ decisions to refuse vaccinations for their young children. The story is predicated on a study in Pediatrics that was released this morning.
Vaccines protect individuals from contracting such diseases as measles, mumps, rubella, diphtheria, tetanus, and pertussis and, what is more, protect others around the individuals. If a high percentage of the population in a given area is vaccinated against a disease, then when the almost-inevitable infection occurs in one or a few individuals, the disease does not sweep rapidly and tragically through that population. This is the so-called “herd immunity.” Importantly, if the herd is safer, then individuals who are not immune are also safer.
Herd immunity is easy to understand when the population is quite large. However, it is important to think about the phenomenon when the population is much smaller. Consider for example if the population is a family group composed of only a few people. The youngest among those may not be able to be vaccinated, but if all the others are vaccinated, then the disease is less likely to strike those young members of the family group. But, if only a few of the family members are vaccinated and one of the individuals contracts the disease, all the other unvaccinated individuals (little brothers, little sisters) are at substantial risk for contracting it, too.
Sadly as J. M. Glanz and his colleagues reported in the journal Pediatrics, when parents refuse pertussis vaccinations for their children, the risk for the infants in the family to contract pertussis increases. The children of parents who refuse pertussis vaccination were about 25 times more likely to contract the disease than those in families where the vaccinations were not refused.
Here is the abstract for the study by Professor Glanz and colleagues:
Glanz, J. M., McClure, D. L., Magid, D. J., Daley, M. F., France, E. K., Salmon, D. A., & Hambridge, S. J. (2009). Parental refusal of pertussis vaccination is associated with an increased risk of pertussis infection in children. Pediatrics, 123, 1446-1451.
OBJECTIVE. The objective of this study was 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.
METHODS. We conducted a case-control study of children enrolled in the Kaiser Permanente of Colorado health plan between 1996 and 2007. Each pertussis case was matched to 4 randomly selected controls. Pertussis case status and vaccination status were ascertained by medical chart review.
RESULTS. We identiﬁed 156 laboratory-conﬁrmed pertussis cases and 595 matched controls. There were 18 (12%) pertussis vaccine refusers among the cases and 3 (0.5%) pertussis vaccine refusers among the controls. Children of parents who refused pertussis immunizations were at an increased risk for pertussis compared with children of parents who accepted vaccinations. In a secondary case-control analysis of children continuously enrolled in Kaiser Permanente of Colorado from 2 to 20 months of age, vaccine refusal was associated with a similarly increased risk of pertussis. In the entire Kaiser Permanente of Colorado pediatric population, 11% of all pertussis cases were attributed to parental vaccine refusal.
CONCLUSIONS. Children of parents who refuse pertussis immunizations are at high risk for pertussis infection relative to vaccinated children. Herd immunity does not seem to completely protect unvaccinated children from pertussis. These ﬁndings stress the need to further understand why parents refuse immunizations and to develop strategies for conveying the risks and beneﬁts of immunizations to parents more effectively.
This study makes me want to dig through my old posts and find the one where I suggested that society create an island for all those who want to refuse scientifically sensible medical care. Let those folks live there and evolve on their own.
Link to the Glanz et al. study.