Impact of public health responses during a measles outbreak in an Amish community in Ohio: modelling the dynamics of transmission

Abstract

We quantified measles transmissibility during a measles outbreak in Ohio in 2014 to evaluate the impact of public health responses. Case incidence and the serial interval (time between symptom onset in primary and secondary cases) were used to assess trends in the effective reproduction number R (average number of secondary cases generated per case). A mathematical model was parameterized by early R values to determine outbreak size and duration if containment measures had not been initiated, and the impact of vaccination. As containment started, we found a fourfold decline in R (~4 to 1) over 2 weeks, and maintenance of R < 1 as control measures continued. Under a conservative scenario, the model estimated 8,472 cases (90% confidence interval [CI]: 8,447, 8,489) over 195 days (90% CI: 179, 223) without control efforts, and 715 cases (90% CI: 103, 1,338) over 128 days (90% CI: 117, 139) when including vaccination; 7,757 fewer cases (90% CI: 7,130, 8,365) and 67 fewer outbreak days (90% CI: 48, 98) were attributed to vaccination. Vaccination may not account entirely for transmission reductions, suggesting changes in community behavior (social distancing) and other control efforts (isolation, quarantining) are important. Our findings highlight the benefits of measles outbreak response and of understanding behavior change dynamics.