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

Grais, R.F.; Ferrari, M.J.; Dubray, C.; Bjørnstad, O.N.; Grenfell, B.T.; Djibo, A.; Fermon, F.; Guerin, P.J.

doi:10.1016/j.trstmh.2005.10.014

« Previous Next »Transactions of the Royal Society of Tropical Medicine and Hygiene
Volume 100, Issue 9 , Pages 867-873, September 2006

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

R.F. Grais
- Epicentre, 8 rue Saint Sabin, 75011 Paris, France
- Corresponding author. Tel.: +33 1 40 21 29 43; fax: +33 1 40 21 28 03.
M.J. Ferrari
- Department of Entomology, 501 ASI Bldg, Penn State University, University Park, PA 16802, USA
C. Dubray
- Epicentre, 8 rue Saint Sabin, 75011 Paris, France
O.N. Bjørnstad
- Department of Entomology, 501 ASI Bldg, Penn State University, University Park, PA 16802, USA
- Fogarty International Center, National Institutes of Health, Bethesda, MD 20892, USA
B.T. Grenfell
- Department of Entomology, 501 ASI Bldg, Penn State University, University Park, PA 16802, USA
- Fogarty International Center, National Institutes of Health, Bethesda, MD 20892, USA
A. Djibo
- Ministry of Health, Niamey, Niger
F. Fermon
- Médecins Sans Frontières, 8 rue Saint Sabin, 75011 Paris, France
P.J. Guerin
- Epicentre, 8 rue Saint Sabin, 75011 Paris, France

Received 4 July 2005; received in revised form 17 October 2005; accepted 18 October 2005.

Summary

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.

Keywords: Measles, Vaccination, Epidemic modelling, Reproductive ratio, Niger