Fig. 5

Increased attack rates in an age-specific epidemic model. Variation in duration of immunity increases the epidemic peak (a) and the attack rates in the unvaccinated (b) as well as in the vaccinated (c) subpopulations. In this model we assume a leaky vaccine, use age-specific contact patterns, and take realistic latent and infectious periods (using two latent compartments and two infectious compartments). The time series shows periodic behavior with periods of 2 and 3 years (at vaccination coverages 0-13% and 14-15%, respectively) for the scenario with constant duration of immunity. Shown are the averages of the periodic epidemics, explaining the irregularity of the blue curves. Percentile bands are not drawn in b and c