Kristie McNealy, MD

A new study out of Colorado has shown that parents can’t depend on “herd immunity” to protect their children from vaccine preventable diseases.  The study, which was a collaborative effort between the University of Colorado, Kaiser Permanente Colorado, Johns Hopkins Bloomberg School of Public Health, and Community Health Services, Denver, was published in the journal Pediatrics.

Researchers performed a case control study of Colorado children enrolled in Kaiser Permanente between 1996 and 2007, comparing those children that had a confirmed diagnosis of pertussis (whooping cough) to a group of gender and age matched controls.

In all, investigators studied 156 children with laboratory-confirmed pertussis cases and 595 matched control.  The findings showed that children who were unvaccinated had a nearly 23 times higher risk of contracting pertussis.  In addition, vaccine refusers made up 12% of confirmed pertussis cases, despite the fact that they made up only 0.5% of the control population, which was selected by age, gender and Kaiser enrollment criteria, not vaccination status.

In order to keep vaccine preventable diseases to a minimum, adequate vaccination coverage is required for herd immunity to protect those that are medically unable or too young to receive a vaccine, or unable to produce an adequate immune response to vaccines.  Unfortunately, a failing immunization program is leaving these individuals in a dangerous situation, a point which is illustrated by the fact that more than 1/2 of all US pertussis deaths reported in a study published in the March 2009 issue of Pediatric Infectious Disease were in infants under two months of age.

The current recommended schedule for the DTaP vaccine which protects against diptheria, tetanus and pertussis is a series of four doses given at 2 months, 4 months, 6 months and 15-18 months of age, followed by a booster given before kindergarten.

As a Colorado resident and mom (as well as an MD), this particular study strikes close to home.  While I understand and value the importance of personal choice and the freedom of individuals to dictate their medical care, and I stand opposed to government mandates forcing us to put things in our bodies, I find myself troubled by the reasoning presented by many vaccine refusing families I know.  The argument that a particular child is vaccinated and “has always been healthy” is one that falls apart quickly when that child actually catches a vaccine preventable disease.

At one time, in our not so distant past, parents expected to bury their children.  It was the tragic norm to have lost at least one child to an outbreak of the diseases we are now lucky to be able to control and prevent with vaccines.  Those that choose not to vaccinate because it is unnecessary, or because they think that pertussis is “just a cough” or measles is “just a rash” have clearly never seen a person die from one of these diseases.  I hope they never do.

Reference: 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.

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