Mortality burden from seasonal influenza and 2009 H1N1 pandemic influenza in Beijing, China, 2007‐2013

Abstract

BackgroundData about influenza mortality burden in northern China are limited. This study estimated mortality burden in Beijing associated with seasonal influenza from 2007 to 2013 and the 2009 H1N1 pandemic.MethodsWe estimated influenza‐associated excess mortality by fitting a negative binomial model using weekly mortality data as the outcome of interest with the percent of influenza‐positive samples by type/subtype as predictor variables.ResultsFrom 2007 to 2013, an average of 2375 (CI 1002‐8688) deaths was attributed to influenza per season, accounting for 3% of all deaths. Overall, 81% of the deaths attributed to influenza occurred in adults aged ≥65 years, and the influenza‐associated mortality rate in this age group was higher than the rate among those aged <65 years (113.6 [CI 49.5‐397.4] versus 4.4 [CI 1.7‐18.6] per 100 000, P < .05). The mortality rate associated with the 2009 H1N1 pandemic in 2009/2010 was comparable to that of seasonal influenza during the seasonal years (19.9 [CI 10.4‐33.1] vs 17.2 [CI 7.2‐67.5] per 100 000). People aged <65 years represented a greater proportion of all deaths during the influenza A(H1N1)pdm09 pandemic period than during the seasonal epidemics (27.0% vs 17.7%, P < .05).ConclusionsInfluenza is an important contributor to mortality in Beijing, especially among those aged ≥65 years. These results support current policies to give priority to older adults for seasonal influenza vaccination and help to define the populations at highest risk for death that could be targeted for pandemic influenza vaccination.

State‐level estimates of excess hospitalizations and deaths associated with influenza

“…During 2009, the numbers and rates of excess hospitalizations and deaths attributed to influenza A(H1N1) were disproportionately high among persons aged <65 years, particularly among infants. The left shift in the age distribution of morbidity and mortality due to pandemic influenza A(H1N1) is thought to result from the presence of pre‐existing immunity among persons in older birth cohorts due to prior exposure to antigenically similar H1N1 viruses . In our study, influenza A(H1N1) continued to be associated with relatively high rates of excess hospitalization and death among the younger age groups when circulating during seasons following the pandemic.…”

“…One was the inability to account for respiratory syncytial virus (or other seasonal potential confounders) in our models, which may have led to overestimation in our results for influenza. However, other investigators have considered respiratory syncytial virus to be captured by the seasonal baseline . Another potential limitation was that influenza testing practices changed following the 2009 pandemic, which may have affected our virus surveillance data .…”

“…The above findings and our approach to estimating the state‐level burden of influenza apply to broader public health prevention and response efforts in several ways. First, we demonstrated that it is feasible to calculate state‐level estimates of influenza burden using methods established for national public health purposes . Second, the approach accounted for the known under‐detection of influenza inherent to surveillance based on laboratory diagnosis or direct review of influenza diagnoses in administrative records .…”

“…We, therefore, adapted CDC's methods and analogous methods from similar studies to estimate influenza excess hospitalizations and deaths in Colorado. [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] We demonstrate that periodic disease burden estimates are feasible and provide additional information about serious influenza outcomes not routinely available in a state.…”

“…The application of similar estimation methods to state‐level data has the potential to provide local burden estimates that complement existing influenza surveillance. We, therefore, adapted CDC’s methods and analogous methods from similar studies to estimate influenza excess hospitalizations and deaths in Colorado . We demonstrate that periodic disease burden estimates are feasible and provide additional information about serious influenza outcomes not routinely available in a state.…”