Abstract
Due to differences in the circulation of influenza viruses, distribution and antigenic drift of A subtypes and B lineages, and susceptibility to infection in the population, the incidence of symptomatic influenza infection can vary widely between seasons and age-groups. Our goal was to estimate the symptomatic infection incidence in the Netherlands for the six seasons 2011/2012 through 2016/2017, using Bayesian evidence synthesis methodology to combine season-specific sentinel surveillance data on influenza-like illness (ILI), virus detections in sampled ILI cases and data on healthcare-seeking behaviour. Estimated age-aggregated incidence was 6.5 per 1000 persons (95% uncertainty interval (UI): 4.7-9.0) for season 2011/2012, 36.7 (95% UI: 31.2-42.8) for 2012/2013, 9.1 (95% UI: 6.3-12.9) for 2013/2014, 41.1 (95% UI: 35.0-47.7) for 2014/2015, 39.4 (95% UI: 33.4-46.1) for 2015/2016 and 27.8 (95% UI: 22.7-33.7) for season 2016/2017. Incidence varied substantially between age-groups (highest for the age-group <5 years: 23 to 47/1000, but relatively low for 65+ years: 2 to 34/1000 over the six seasons). Integration of all relevant data sources within an evidence synthesis framework has allowed the estimation - with appropriately quantified uncertainty - of the incidence of symptomatic influenza virus infection. These estimates provide valuable insight into the variation in influenza epidemics across seasons, by virus subtype and lineage, and between age-groups.
Highlights
Characteristics of the seasonal influenza epidemic that annually occurs in the northern hemisphere winter vary greatly between seasons
A frequently applied – indirect – approach for monitoring the seasonal influenza epidemic and measuring variation in intensity across seasons is through the incidence of influenza-like illness (ILI) from sentinel general practitioner (GP) networks, and/or the incidence of severe acute respiratory infection (SARI) from hospital surveillance [3]
The circulation of other respiratory viruses differs between seasons, which means that reliance on ILI or SARI data alone does not provide an accurate picture of the influenza epidemic intensity
Summary
Characteristics of the seasonal influenza epidemic that annually occurs in the northern hemisphere winter vary greatly between seasons (usually defined as week 40 through week 20 of the following year). Of the drivers of variation in transmission intensity between seasons [1], the dominant type (A or B), subtype (of influenza A) or lineage (of influenza B) of the circulating influenza viruses is a key factor. A frequently applied – indirect – approach for monitoring the seasonal influenza epidemic and measuring variation in intensity across seasons is through the incidence of influenza-like illness (ILI) from sentinel general practitioner (GP) networks, and/or the incidence of severe acute respiratory infection (SARI) from hospital surveillance [3]. The circulation of other respiratory viruses differs between seasons, which means that reliance on ILI or SARI data alone does not provide an accurate picture of the influenza epidemic intensity
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