Incubation period of influenza A and B viruses

The incubation period for influenza A virus typically lasts 2–7 days, while that of influenza B virus is longer, generally lasting 7–14 days and sometimes extending to 20 days or more. Influenza A and B viruses are the two main types responsible for seasonal influenza. The incubation period is an important indicator for determining whether a person has been exposed to the virus, thereby guiding subsequent treatment plans and helping reduce societal impact. For influenza A, clinical symptoms such as runny nose, cough, and fever usually begin to appear within 2–7 days after infection; once these symptoms emerge, infection with influenza A can be diagnosed. In contrast, the incubation period for influenza B virus is longer—typically 7–14 days—and infections may lead to more severe and prolonged symptoms. Therefore, prompt diagnosis is essential so that timely treatment measures can be initiated.