Researchers analyzed blood samples from volunteers in Southern China and found that while children get flu on average every other year, flu infections become less frequent as people progress through childhood and early adulthood; and from the age of 30 onwards, flu infections tend to occur at a steady rate of about two per decade. Possibly this increased frequency of infections in childhood and adolescence could be because youngsters tend to mix more with other people. However, the researchers noted that the exact frequency of infection will vary depending on background levels of flu and vaccination.
Adam Kucharski said, "There's a lot of debate in the field as to how often people get flu, as opposed to flu-like illness caused by something else. These symptoms could sometimes be caused by common cold viruses, such as rhinovirus or coronavirus. Also, some people might not realize they had flu, but the infection will show up when a blood sample is subsequently tested."