IJE Advance Access originally published online on March 24, 2004
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International Journal of Epidemiology, Volume 33, Number 3, pp. 566-572
IJE vol.33 no.3 © International Epidemiological Association 2004; all rights reserved.
Article |
Ageing populations and childhood infections: the potential impact on epidemic patterns and morbidity
1 Department of Infectious Disease Epidemiology, Imperial College London, W2 1PG, UK
2 Dipartimento di Statistica e Matematica Applicata all'Economia, Università di Pisa, Via C Ridolfi 10, 56124 Pisa, Italy
Correspondence: Department of Infectious Disease Epidemiology, Division of Primary Care and Population Health Sciences, Faculty of Medicine, Imperial College London, Norfolk Place, London W2 1PG, UK. E-mail: jr.williams{at}imperial.ac.uk
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.
Keywords Age distribution, childhood infections, fertility, health transition, health planning, immunization programs, Italy, mathematical model, measles, non-linear dynamics, population decline, population dynamics, rubella, theoretical models, vaccination coverage
Accepted 17 December 2003
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