Managing the risks of vaccine hesitancy and refusals

In The Lancet Infectious Diseases, John Glasser and colleagues report the results of a spatially-stratified model to better understand the dynamics of disease outbreaks and the link with vaccine hesitancy and refusal. Using data for 39 132 children starting elementary school in San Diego County, CA, USA, in 2008 (2% of whom had a personal-belief exception to vaccines), the authors show the effect of heterogeneity on the reproduction numbers for measles, mumps, and rubella. Although the mean population immunities for measles, mumps, and rubella were similar to the population-immunity thresholds, modelling for non-random mixing (unvaccinated children tend to preferentially mix with other unvaccinated children) and heterogeneity caused the basic reproductive numbers to increase by 70%, meaning that an introduced infectious person could cause an outbreak.