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Three Quarters of People Infected With Flu Show No Symptoms

March 21, 2014
Public Health

A new study comparing the severity of seasonal and pandemic influenza over a five year period has found more than three quarters of those infected failed to develop any symptoms. The Flu Watch Study tracked five successive groups of households across England over six flu seasons between 2006 and 2011. Participants who were contacted weekly to report any symptoms such as colds or coughs provided blood samples before and after each flu season. Results revealed that approximately 18% of the unvaccinated community became infected with flu each winter but 77% of those infected showed no symptoms of the illness. 

Dr Andrew Hayward from University College London feels that the findings show that the number of infections in the community have been greatly underestimated. “Reported cases of influenza represent the tip of a large clinical and subclinical iceberg that is mainly invisible to national surveillance systems that only record cases seeking medical attention,” he said, adding, “Most people don’t go to the doctor when they have flu. Even when they do consult they are often not recognised as having influenza.”

The use of anti viral drug Tamiflu saved lives during the 2009 swine flu pandemic according to a separate report this week. Analysis of data involving more than 29,000 patients from 38 countries found that the drug reduced the risk of death by 19%. 

The abstract to the Flu Watch Study can be found here.