Overview

The updated WHO pandemic influenza severity assessment (PISA) framework set out in this document provides a systematic approach for interpreting data collected through existing surveillance systems and improving their usefulness for risk communication and decision-making. The approach enables the severity of current influenza and syndromic respiratory illness activity to be assessed relative to previous years by using historical data to set thresholds that then allow for the qualitative categorization of such activity. PISA is designed to be implemented continuously based on stable/ routine reporting systems, enabling activity during epidemic and pandemic periods to be compared. Information to assess severity especially early and throughout the course of a pandemic will also be provided through investigations, studies and modelling.