Abstract
Background: Assessment of the effect of influenza on populations, including risk of infection, illness if infected, illness severity, and consultation rates, is essential to inform future control and prevention. We aimed to compare the community burden and severity of seasonal and pandemic influenza across different age groups and study years and gain insight into the extent to which traditional surveillance underestimates this burden. Methods: Using preseason and postseason serology, weekly illness reporting, and RT-PCR identification of influenza from nasal swabs, we tracked the course of seasonal and pandemic influenza over five successive cohorts (England 2006-11; 5448 person-seasons' follow-up). We compared burden and severity of seasonal and pandemic strains. We weighted analyses to the age and regional structure of England to give nationally representative estimates. We compared symptom profiles over the first week of illness for different strains of PCR-confirmed influenza and non-influenza viruses using ordinal logistic regression with symptom severity grade as the outcome variable. Findings: Based on four-fold titre rises in strain-specific serology, on average influenza infected 18% (95% CI 16-22) of unvaccinated people each winter. Of those infected there were 69 respiratory illnesses per 100 person-influenza-seasons compared with 44 per 100 in those not infected with influenza. The age-adjusted attributable rate of illness if infected was 23 illnesses per 100 person-seasons (13-34), suggesting most influenza infections are asymptomatic. 25% (18-35) of all people with serologically confirmed infections had PCR-confirmed disease. 17% (10-26) of people with PCR-confirmed influenza had medically attended illness. These figures did not differ significantly when comparing pandemic with seasonal influenza. Of PCR-confirmed cases, people infected with the 2009 pandemic strain had markedly less severe symptoms than those infected with seasonal H3N2. Interpretation: Seasonal influenza and the 2009 pandemic strain were characterised by similar high rates of mainly asymptomatic infection with most symptomatic cases self-managing without medical consultation. In the community the 2009 pandemic strain caused milder symptoms than seasonal H3N2. Funding: Medical Research Council and the Wellcome Trust.
| Original language | English |
|---|---|
| Pages (from-to) | 445-454 |
| Number of pages | 10 |
| Journal | The Lancet Respiratory Medicine |
| Volume | 2 |
| Issue number | 6 |
| DOIs | |
| Publication status | Published - Jun 2014 |
Bibliographical note
Funding Information:JSN-V-T has served on speaker bureaus for, served as a consultant to, and received grants and support for travel from Roche and GSK, but all personal remuneration stopped in Sept, 2010. He also received support for travel from Roche. IN was funded by GSK as chief investigator on a prospective, observational, multicentre, cohort, post-authorisation safety study of GlaxoSmithKline Biologicals A/California/7/2009 (H1N1) v-like pandemic vaccine adjuvanted with AS03. This study was part of the Medicines and Healthcare products Regulatory Agency's procedures for approval of the vaccination from 2009 to 2011. MZ has received funding from vaccine companies (Sanofi, Novartis, CSL, Baxter, GSK) and Roche for antiviral work. AMJçs been a Governor of the Wellcome Trust since 2011. ACH, WJE, NF, JSN-V-T, RP, JMW, and MZ have served on UK national advisory committees relevant to planning and response for seasonal and pandemic influenza. Authors not specifically mentioned declare that they have no competing interests.