title: Revealing the True Incidence of Pandemic A(H1N1)pdm09 Influenza in Finland during the First Two Seasons - An Analysis Based on a Dynamic Transmission Model.
abstract: The threat of the new pandemic influenza A(H1N1)pdm09 imposed a heavy burden on the public health system in Finland in 2009-2010. An extensive vaccination campaign was set up in the middle of the first pandemic season. However, the true number of infected individuals remains uncertain as the surveillance missed a large portion of mild infections. We constructed a transmission model to simulate the spread of influenza in the Finnish population. We used the model to analyse the two first years (2009-2011) of A(H1N1)pdm09 in Finland. Using data from the national surveillance of influenza and data on close person-to-person (social) contacts in the population, we estimated that 6% (90% credible interval 5.1 - 6.7%) of the population was infected with A(H1N1)pdm09 in the first pandemic season (2009/2010) and an additional 3% (2.5 - 3.5%) in the second season (2010/2011). Vaccination had a substantial impact in mitigating the second season. The dynamic approach allowed us to discover how the proportion of detected cases changed over the course of the epidemic. The role of time-varying reproduction number, capturing the effects of weather and changes in behaviour, was important in shaping the epidemic.
authors.affiliation: University of Helsinki, Helsinki, Finland.|National Institute for Health and Welfare, Helsinki, Finland.
authors.forename: Mikhail
authors.initials: M
authors.lastname: Shubin
authors.affiliation: Rybinsk State Aviation Technical University, Rybinsk, Russia.
authors.forename: Artem
authors.initials: A
authors.lastname: Lebedev
authors.affiliation: National Institute for Health and Welfare, Helsinki, Finland.
authors.forename: Outi
authors.initials: O
authors.lastname: Lyytikäinen
authors.affiliation: National Institute for Health and Welfare, Helsinki, Finland.|University of Turku, Turku, Finland.
authors.forename: Kari
authors.initials: K
authors.lastname: Auranen
mesh_terms: D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D003198:Computer Simulation; D003627:Data Interpretation, Statistical; D005260:Female; D005387:Finland / Q000453:epidemiology; D006801:Humans; D015994:Incidence; D007223:Infant; D007231:Infant, Newborn; D007252:Influenza Vaccines / Q000627:therapeutic use; D007251:Influenza, Human / Q000453:epidemiology* / Q000517:prevention & control*; D008297:Male; D032541:Mass Vaccination / Q000706:statistics & numerical data; D008875:Middle Aged; D015233:Models, Statistical; D058873:Pandemics / Q000517:prevention & control* / Q000706:statistics & numerical data*; D015203:Reproducibility of Results; D018570:Risk Assessment / Q000379:methods; D012621:Seasons; D012680:Sensitivity and Specificity; D017678:Sex Distribution; D055815:Young Adult
chemical_list: D007252:Influenza Vaccines