Influenza A viruses are the most harmful, as they can cause severe disease.influenza is usually responsible for the majority of seasonal flu cases. It is found in humans and in animals. Influenza A is spread from person to person by people who are already infected. Touching objects the infected person has touched or even being in the same room as the person, especially if they are coughing or sneezing, is enough to become infected yourself.
Influenza B almost exclusively infects