- Occurrence (distribution by age, season, serotype), type of community (open/closed) and severity of disease including CFR (case fatality rate)

- Incubation, transmission and exposure period

- Chemoprophylaxis of contacts and vaccination of high risk group

Steps/outcomes of outbreak control

- Protect close contacts: Identify them and provide prophylactic drugs

2. Prevent spread in open/closed communities by vaccinating people at risk

3. Active surveillance of new cases

4. Consistent communication of events and control actions to media, community and health care providers

Critical: quick action and completeness of investigation and prophylaxis/vaccination