A link between the North Atlantic Oscillation and measles dynamics during the vaccination period in England and Wales

Ecologists have become aware of the role played by interannual climatic variability on the temporal dynamics of infectious diseases. In this report, I present evidence from data on measles cases in England and Wales showing that during the post-vaccination period, the interannual variability of winter weather (represented by the North Atlantic Oscillation, NAO) influences the annual dynamics of the disease. Using annual measles data from seven cities and simple logistic models, this study reveals how, after vaccination, NAO increases its effects on measles fluctuations. In addition, this study shows that vaccination may be represented as a simple vertical and lateral perturbation effect (Royama's classification), by reducing the maximum per capita growth rate and the equilibrium number of infected individuals. The results suggest that vaccination will not lead to outbreaks of measles from regular cyclic to irregular chaotic dynamics. In contrast, because of the reduction in per capita growth rates, the disease dynamics appear to be more stable than during the pre-vaccination period. The analysis of annual data on infectious diseases may be useful for detecting long-term effects of climate and complements the classical analyses and modeling based on monthly or seasonal time-step data.