Comparative community burden and severity of seasonal and pandemic influenza: results of the Flu Watch cohort study

摘要: Summary Background Assessment of the effect influenza on populations, including risk infection, illness if infected, severity, and consultation rates, is essential to inform future control prevention. We aimed compare community burden severity seasonal pandemic across different age groups study years gain insight into extent which traditional surveillance underestimates this burden. Methods Using preseason postseason serology, weekly reporting, RT-PCR identification from nasal swabs, we tracked course over five successive cohorts (England 2006–11; 5448 person-seasons' follow-up). compared strains. weighted analyses regional structure England give nationally representative estimates. symptom profiles first week for strains PCR-confirmed non-influenza viruses using ordinal logistic regression with grade as outcome variable. Findings Based four-fold titre rises in strain-specific average infected 18% (95% CI 16–22) unvaccinated people each winter. Of those there were 69 respiratory illnesses per 100 person-influenza-seasons 44 not influenza. The age-adjusted attributable rate was 23 person-seasons (13–34), suggesting most infections are asymptomatic. 25% (18–35) all serologically confirmed had disease. 17% (10–26) medically attended illness. These figures did differ significantly when comparing cases, 2009 strain markedly less severe symptoms than H3N2. Interpretation Seasonal characterised by similar high rates mainly asymptomatic infection symptomatic cases self-managing without medical consultation. In caused milder Funding Medical Research Council Wellcome Trust.