The finding will help scientists understand how the disease spreads, who is likely to get sick, and how to develop new vaccines that keep the disease in check effectively, scientists indicated in the study.
“For adults, we found that influenza infection is actually much less common than some people think. In childhood and adolescence, it’s much more common, possibly because we mix more with other people,” said Mr. Steven Riley of Imperial College London, who worked on the research.
For the study, researchers examined blood samples from volunteers in Southern China and looked at antibodies levels against nine strains of flu that affected the population from 1968 to 2009.
Scientists found that children get flu on average every other year, but infections less frequent with age. Illnesses with “flu-like” symptoms are often caused by other bugs such as rhinoviruses and coronaviruses, which makes it difficult for individuals to know if they have the real flu, the researchers said.
The team, which included researchers from Britain, the United States and China, came up with a mathematical model of how immunity to flu changes across the lifetime as people run into several virus strains.
“What we’ve done in this study is to analyze how a person’s immunity builds up over a lifetime of flu infections,” said Mr. Adam Kucharski, of London School of Hygiene & Tropical Medicine.