The Influenza Risk Assessment Tool (IRAT) is an evaluation tool developed by CDC and external influenza experts that assesses the potential pandemic risk posed by influenza A viruses that currently circulate in animals but not in humans. The IRAT assesses potential pandemic risk based on two different scenarios: “emergence” and “public health impact.”
“Emergence” refers to the risk of a novel (i.e., new in humans) influenza virus acquiring the ability to spread easily and efficiently in people. “Public health impact” refers to the potential severity of human disease caused by the virus (e.g., deaths and hospitalizations) as well as the burden on society (e.g., missed workdays, strain on hospital capacity and resources, and interruption of basic public services) if a novel influenza virus were to begin spreading efficiently and sustainably among people.
The IRAT uses 10 scientific criteria to measure the potential pandemic risk associated with each of these scenarios. These 10 criteria can be grouped into three overarching categories: “properties of the virus,” “attributes of the population,” and “ecology & epidemiology of the virus.” Influenza subject matter experts evaluate novel influenza viruses based on each of these 10 criteria. Each of the 10 criteria is then weighted statistically based on its significance to each of the two scenarios. A composite score for each virus is then calculated based on the given scenario. These composite scores provide a means to rank and compare influenza viruses to each other in terms of their potential pandemic risk for each of the two scenarios.
As we learn more about influenza A viruses, these 10 criteria may change, other criteria may be added or some current criteria may be dropped. The IRAT is designed to be flexible and responsive to current scientific advances.