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A meta-analysis of studies of influenza A (H1N1) infection in 2009 showed that healthcare workers were twice as likely to have influenza than non-healthcare workers and healthcare workers can transmit influenza without knowing they are infected.(2,3) In general, around 10%of adults who do not receive an influenza vaccination catch influenza annually and approximately half of these cases are asymptomatic.
Influenza does not always cause symptoms or make a person feel unwell.(5-8)Data from the Southern Hemisphere Influenza and Vaccine Effectiveness Researchand Surveillance (SHIVERS) study, based in Auckland, suggest that four out offive children and adults (80%) with influenza did not have symptoms.(4) In anearlier study following the 2009 influenza season in New Zealand, almost onequarter of the adults who reported that they had not had influenza in 2009 hadserological evidence of prior infection (21% [95% confidence interval13–30%]).(9)
Healthcare workers have a duty of care to protect vulnerable patients from the serious health threat of influenza illness. Studies demonstrate that annual influenza vaccination for healthcare workers is likely to reduce illness among the patients they care for.(10-12) Relying on patients being vaccinated is not enough as vulnerable people may have a poor immune response to their vaccination or may not have been vaccinated this year.