Source: Feikin DR, Lezotte DC, Hamman RF, et al. Individual and community risk of measles and pertussis associated with personal exemptions to immunizations. JAMA. 2000;284:3145–3150.Investigators from the Colorado Department of Public Health and the Centers for Disease Control and Prevention determined the individual and community risks of measles and pertussis associated with lack of immunization because of personal exemptions (religious and philosophical). Colorado children between 3 and 18 years of age during 1987 to 1998 were included in this population-based, retrospective cohort study using standardized records. The percentage of Colorado children with personal exemptions increased from 1.25% to 2.06% from 1987–1998. During the 12-year study period, 505 confirmed measles cases and 1140 confirmed or probable pertussis cases occurred in Colorado, with 40% and 47% of the respective totals occurring in children age 3–18 years. Community risks for measles and pertussis were assessed at the county and school level. Outbreaks were evaluated to determine if their likelihood could be predicted by the proportion of children with personal exemptions (exemptors) in a school.On average, exemptors were 22 times more likely to develop measles than were vaccinated children, and exemptors aged 3–10 years were 62 times more likely. On average the risk for pertussis was 6 to 11 times higher in exemptors, and for exemptors aged 3–10 years the risk was 16 to 26 times greater; this age group also had the highest incidence of pertussis among exemptors.The risk of both measles and pertussis for vaccinated children aged 3–18 years was directly related to the frequency of exemptors in their county of residence (for measles RR=1.6; 95% CI, 1.0–2.4; for pertussis RR=1.9; 95% CI, 1.2–2.1). Schools with outbreaks of each disease had more exemptors compared to schools without outbreaks, although this was statistically significant for pertussis only (for measles P=.26; for pertussis P=.001). For each 1% increase in exemptors in a school, the risk of pertussis increased by 12% (OR 1.12; 95% CI, 1.05–1.20). Exemptors were more likely than non-exemptors to be the index case in an outbreak and, therefore, more likely to initiate outbreaks of both measles and pertussis. Both exemptors and vaccinated children were more likely to acquire measles from an exemptor, and a cluster of exemptors with measles was likely to perpetuate an outbreak.The article by Feikin et al should give pause to those who wish to replace mandatory with voluntary immunization at school entry. This study clearly shows that unimmunized children are not only themselves at risk for measles and pertussis (and perhaps other diseases) but also place immunized children at risk for these diseases because a small proportion of properly immunized children remain susceptible. For example, about 5% of children who receive a single dose of measles vaccine at age 12 months remain susceptible; following a second dose less than 1% are susceptible. Exemptors are also a public health concern. This study shows that exemptors are not only likely to initiate outbreaks at schools, they can also perpetuate the spread and make control of outbreaks more difficult. Immunization is the safest and most cost-effective method of infectious disease prevention. Smallpox has been eliminated and Haemophilus influenzae type b meningitis is almost eliminated. Measles, mumps, rubella, diphtheria and tetanus are rarely reported. Unfortunately, these same successes now contribute to the argument propagated by individuals opposed to immunizations. Because of the very low prevalence of vaccine-preventable diseases, rare side effects of immunization get undue negative publicity and opponents of immunization falsely link vaccines to unproven adverse effects. Furthermore, as pointed out by the accompanying editorial,1 many parents have neither seen nor heard of many of the vaccine-preventable diseases. Therefore, real or imagined side effects of vaccines become deterrents to successful vaccine programs. Fortunately, with some permitted exemptions, childhood immunizations are required by state laws for school and pre-school entry. While there may be legitimate medical reasons for exemptions from immunizations, this study provides strong evidence for the need to immunize all eligible children.Although we have long recognized that high immunization levels are required to control many vaccine-preventable diseases, few communities have assessed the reasons parents claim personal exemptions from school entry requirements, much less attempted to address them. Ultimately, the success of our community immunization programs is sustained by a societal consensus. School entry laws, while necessary, are not sufficient. We must also systematically monitor and address parents’ concerns about immunization, make the case for immunizations, and counter alarming media anecdotes with scientific evidence. Our immunization laws will not endure unless we do the hard work of sustaining the societal consensus that enabled them to be enacted.
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Sep 15, 2021
Tara C Smith 
