Lancet Infect Dis

BackgroundThe goal of vaccination programs designed to prevent outbreaks following the introduction of infectious persons is maintaining the average number of secondary infections per infectious person 64 1. Our aim was to assess heterogeneity in vaccine uptake and other characteristics that, together with non-random mixing, may increase this number and to evaluate strategies to mitigate its impact.MethodsBecause most US children attend elementary school in their own neighborhoods, surveys of children entering kindergarten (attaining 5 years of age before 1 September) permit assessment of spatial heterogeneity in the proportion immune. We obtained results for 39,132 children who began school in 2008 in San Diego County, where a measles outbreak began in a school 12 of whose 40 students (30%) had personal-belief exemptions to vaccination. Using a mixing model suitable for spatially-stratified populations, we calculated the average numbers of secondary infections per infectious person for the diseases against which MMR vaccine protects. We also mapped contributions to this number for measles in San Diego County's 638 schools and its largest District, comprising 200 schools (31%), and determined the impact of plausible interventions to reduce heterogeneity in vaccine uptake.FindingsImpacts ranged from negligible to nearly complete reduction in outbreak potential. Vaccinating the 972 children with personal-belief exemptions was comparable to the most effective intervention considered, vaccinating 638 children attending the 114 schools < 90% of whose students were immune, which increased MMR uptake by 50%.InterpretationInsofar as children with personal-belief exemptions to vaccination not only live in the same households or neighborhoods or attend the same schools, but associate preferentially with other children with like-minded parents, they increase the risk of outbreaks more than may have been appreciated heretofore.20162018-03-20T00:00:00ZCC999999/Intramural CDC HHS/United States26852723PMC5859952714