Epidemiology and Infection

Measles

Modelling the first dose of measles vaccination: the role of maternal immunity, demographic factors, and delivery systems

C. J. E. METCALFa1 c1, P. KLEPACa1, M. FERRARIa2a3, R. F. GRAISa4, A. DJIBOa5 and B. T. GRENFELLa1a3

a1 Department of Ecology and Evolutionary Biology, Princeton University, NJ, USA

a2 Centre for Infectious Disease Dynamics, Pennsylvania State University, PA, USA

a3 Fogarty International Center, National Institute of Health, MD, USA

a4 Epicentre, Paris, France

a5 Ministry of Health, Niger

SUMMARY

Measles vaccine efficacy is higher at 12 months than 9 months because of maternal immunity, but delaying vaccination exposes the children most vulnerable to measles mortality to infection. We explored how this trade-off changes as a function of regionally varying epidemiological drivers, e.g. demography, transmission seasonality, and vaccination coverage. High birth rates and low coverage both favour early vaccination, and initiating vaccination at 9–11 months, then switching to 12–14 months can reduce case numbers. Overall however, increasing the age-window of vaccination decreases case numbers relative to vaccinating within a narrow age-window (e.g. 9–11 months). The width of the age-window that minimizes mortality varies as a function of birth rate, vaccination coverage and patterns of access to care. Our results suggest that locally age-targeted strategies, at both national and sub-national scales, tuned to local variation in birth rate, seasonality, and access to care may substantially decrease case numbers and fatalities for routine vaccination.

(Accepted May 14 2010)

(Online publication June 07 2010)

Correspondence:

c1 Author for correspondence: Dr C. J. E. Metcalf, Department of Ecology and Evolutionary Biology, Eno Hall, Princeton University, Princeton NJ 0854, USA. (Email: cmetcalf@princeton.edu)

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