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Most Flu Is Asymptomatic — Physician’s First Watch
Most Flu Is Asymptomatic
By Joe Elia
Influenza, whether of the seasonal or pandemic variety, is asymptomatic in most people with serologically confirmed infection, according to a study in the Lancet Respiratory Medicine.
Researchers studied five successive cohorts of people in England during the 2006-2011 flu seasons. The cohorts ranged in size from 600 to 3500, and all members provided blood samples before and after each flu season. Their households were contacted weekly to identify flu-like illness and symptoms.
On average, roughly 20% of the unvaccinated had serologic evidence of influenza infection, but up to three quarters of the infected were asymptomatic. The proportions did not vary significantly between seasonal and pandemic influenzas. The pandemic H1N1 strain was associated with less severe symptoms than the seasonal H3N2 strain.
A commentator says an important unanswered question is how much the asymptomatic cases contribute to flu transmission