Influenza infections may be less common that previously estimated, with adults over 30 only becoming infected an average of twice per decade. These study results appear online in the journal PLOS Biology.

A total of 151 children and adults from Southern China contributed a blood sample to evaluate antibody levels against a panel of nine different influenza A (H3N2) strains isolated from 1968–2008. Although children were infected with influenza on average every other year, these infections became less common through childhood and early adulthood. After the age of 30, influenza infections generally occurred twice per decade. A mathematical model developed by the researchers also supported previous evidence that strains of the influenza virus encountered earlier in life may spur greater immune responses vs. those from later in life.

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The authors surmise that frequency of infection may vary due to environmental factors, previous influenza infections, and immunization. In addition, individuals may mistake influenza infections for a flu-like illness caused by common cold viruses like rhinovirus or coronavirus.

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