Objectives: To describe the duration and seasonality of meningitis epidemics in Southern Ethiopia and estimate the proportion of cases prevented by vaccination in order to assess the efficacy of current control strategies.
Methods: A descriptive study of epidemics occurring from 1999 to 2004. The number of cases reported in 24 districts undergoing vaccination campaigns was compared to 36 districts not receiving vaccines or where vaccines had been deployed in the zone.
Results: Sixty epidemics reporting a total of 5806 cases were identified. The duration of the epidemics ranged from 1 to 26 weeks with 45% lasting < or = 6 weeks. Forty-one epidemics reached the WHO epidemic threshold. Seventy-one percent of the cases reported from vaccinated areas occurred in the first 6 weeks compared to 62% in unvaccinated areas and 82% for districts where vaccines had been used in the zone.
Conclusions: The majority of epidemics had a short duration limiting the potential to implement current vaccines effectively. Delivering vaccine to areas adjacent to an epidemic seems to increase their efficacy, however the size of this additional area needs to be better defined.