Adults only tend to catch the flu twice a decade, a study suggests.

The researchers from the Imperial College in London analysed blood samples from volunteers in Southern China, looking at antibody levels against nine different influenza strains that circulated from 1968 to 2009.

They found that while children get flu on average every other year, flu infections become less frequent as they reach adulthood. From the age of 30 onwards, flu infections tend to occur at a steady rate of about two per decade, the study published in PLOS Biology showed.

The results demonstrate the value of interpreting immune responses in the context of a life- time of infection, the authors said.

“Integrating the life course of immunity into future analyses of influenza dy- namics could therefore lead to a better understanding of population susceptibility and the potential transmissibility of new seasonal strains,” they concluded.