Ageing populations and childhood infections: the potential impact on epidemic patterns and morbidity.

BACKGROUND: Population decline, arising from below replacement fertility and possibly giving rise to substantial changes in age distribution, is a feature of many industrialized developed countries; Italy is one of the most notable European examples. The potential influence of this phenomenon on prevalence of chronic non-infectious disease is well known, but little attention to date has been paid to the impact on severe disease due to childhood infections in those cases where control is insufficient to achieve elimination.
METHODS: A transmission dynamics model incorporating realistic demography is used to investigate the possible impact of population decline and ageing and suboptimal vaccination uptake on the age distribution of incidence of measles infection and of consequent mortality. Data from Italy is used to parameterize the model.
RESULTS: Population ageing in the absence of vaccination is shown to reduce per capita incidence of infection but also to increase average and upper quartile ages at infection. The effect is substantially enhanced by significantly suboptimal vaccination uptake, when disease-induced mortality has, for a period, the potential to exceed that in the absence of vaccination.
CONCLUSIONS: Although a substantially increased burden from chronic non-infectious disease has frequently been proposed as a consequence of population decline, there is also potential for an increase in morbidity and mortality from measles and other childhood infectious diseases, particularly where vaccine uptake is substantially below the optimum. Rubella is highlighted as a particular cause for concern. This work also has implications for less-developed countries.