Estimating transmission intensity for a measles epidemic in Niamey, Niger: lessons for intervention

• Published in: Transactions of the Royal Society of Tropical Medicine and Hygiene Vol. 100; no. 9; pp. 867 - 873
• Main Authors: Grais, R.F., Ferrari, M.J., Dubray, C., Bjørnstad, O.N., Grenfell, B.T., Djibo, A., Fermon, F., Guerin, P.J.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01-09-2006; Royal Society of Tropical Medicine and Hygiene; Elsevier
• Subjects: Age Distribution; Biological and medical sciences; Child, Preschool; Disease Outbreaks - prevention & control; Epidemic modelling; Human viral diseases; Humans; Infant; Infectious diseases; Measles; Measles - epidemiology; Measles - prevention & control; Measles - transmission; Measles Vaccine - therapeutic use; Medical sciences; Models, Biological; Niger; Niger - epidemiology; Prospective Studies; Reproductive ratio; Retrospective Studies; Urban Health; Vaccination; Vaccination - methods; Viral diseases; Viral diseases with cutaneous or mucosal lesions and viral diseases of the eye; Niger; Africa; Epidemic modelling; Niger; Measles; Vaccination; Reproductive ratio; Infection; Epidemic; Human; Viral disease; Transmission; Tropical medicine; Epidemiology
• ISSN: 0035-9203; 1878-3503
• DOI: 10.1016/j.trstmh.2005.10.014

The objective of this study is to estimate the effective reproductive ratio for the 2003–2004 measles epidemic in Niamey, Niger. Using the results of a retrospective and prospective study of reported cases within Niamey during the 2003–2004 epidemic, we estimate the basic reproductive ratio, effective reproductive ratio (RE) and minimal vaccination coverage necessary to avert future epidemics using a recent method allowing for estimation based on the epidemic case series. We provide these estimates for geographic areas within Niamey, thereby identifying neighbourhoods at high risk. The estimated citywide RE was 2.8, considerably lower than previous estimates, which may help explain the long duration of the epidemic. Transmission intensity varied during the course of the epidemic and within different neighbourhoods (RE range: 1.4–4.7). Our results indicate that vaccination coverage in currently susceptible children should be increased by at least 67% (vaccine efficacy 90%) to produce a citywide vaccine coverage of 90%. This research highlights the importance of local differences in vaccination coverage on the potential impact of epidemic control measures. The spatial–temporal spread of the epidemic from district to district in Niamey over 30 weeks suggests that targeted interventions within the city could have an impact.