The main source of information during an influenza pandemic will come from well-placed and well-timed public health investigations and systematically and consistently collected surveillance data. During an influenza pandemic, these data will let us know how many cases are occurring in a country, who is most affected, where cases are occurring, how severe illnesses are, the use and effectiveness of interventions, and how health systems are being used. Such data are critical so that public health leaders can make informed, evidence-based decisions to reduce morbidity and mortality during the pandemic.

Consistent surveillance for influenza will be important during a pandemic to help monitor the situation. WHO has provided guidance to countries on the types of surveillance data to collect during an influenza pandemic and how those data can be used to describe the severity of an ongoing pandemic compared with seasonal influenza activity. This guidance will help countries prepare for influenza pandemics. This guidance will also help create a collaborative and coordinated global response to an influenza pandemic. WHO is updating the 2017 guidance for surveillance during a pandemic below.