So far 7,595 cases have been reported from the WHO African Region in 1998. However not all countries are experiencing this generally reduced level of activity. In recent weeks there has been a large outbreak in Chad. From 29 December 1997 to 22 March 1998 there were 2,835 cases and 239 deaths reported from Chad. Vaccination campaigns have been carried out in districts where the weekly attack rate has exceeded 5 cases per 100,000 population.
Early detection is crucial to the ability to mount a response to control epidemics.