Many adults report getting "flu" most winters – but in fact they are likely to contract it about twice a decade, according to a new study.
Many other disease-causing agents can cause flu-like illnesses, say Dr Adam Kucharski of the London School of Hygiene & Tropical Medicine, UK, and colleagues.
The team investigated the real prevalence of flu by analysing blood samples from volunteers in Southern China. The antibodies in these samples were compared with nine different strains of flu which were in circulation between 1968 and 2009.
This showed that flu infections get less frequent as we age, from a rate of every two years in children to every five years from the age of 30.
This is the first time a research team has reconstructed a group’s history of infection from modern-day blood samples. They also showed that the blood retains antibodies for flu strains the immune system has previously encountered. So strains of the virus that are encounter earlier in life evoke stronger immune responses.
"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," said Dr Kucharski. "These symptoms could sometimes be caused by common cold viruses, such as rhinovirus or coronavirus. Also, some people might not realise they had flu, but the infection will show up when a blood sample is subsequently tested."
He adds: "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."
Details appear today in the journal PLoS Biology.
Kucharski, A.J. et al. Estimating the life course of influenza A(H3N2) antibody responses from cross-sectional data. PLoS Biology 4 March 2015 [abstract]
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