Most people get the flu less often than they think

Photo: Sean Gallup / Getty Images.

Most adults get the flu less often than they thing. A study has found adults over the age of 30 only catch flu about twice a decade.

The research, published in the journal PLOS Biology, says flu-like illness can be caused by many pathogens, making it difficult to assess how often people get binfluenza.

The immune system responds to flu viruses by producing antibodies which target proteins on the virus surface. These proteins can change as the virus evolves but antibodies in the blood have a memory for strains encountered before.

Researchers 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 people move through childhood and early adulthood.

From the age of 30 onward, flu infections tend to occur at a steady rate of about two per decade.

Dr Adam Kucharski, who worked on the study at Imperial College London before moving to the London School of Hygiene & Tropical Medicine, 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.”

Some people might not realise they’ve had flu but the infection will show up when a blood sample is tested. This is the first time anyone has reconstructed a group’s history of infection from modern-day blood samples.

For adults, the study found that influenza infection is much less common than most people think.

The findings will help understanding how the immunity in the population affects the evolution of flu viruses, and potentially make predictions about how the virus will change in the future.

Dr Kucharski said: “What we’ve done in this study is to analyse how a person’s immunity builds up over a lifetime of flu infections. This information helps us understand the susceptibility of the population as a whole and how easy it is for new seasonal strains to spread through the population.”

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