title: Different transmission patterns in the early stages of the influenza A(H1N1)v pandemic: a comparative analysis of 12 European countries.
abstract: Following the emergence of a novel strain of influenza A(H1N1) in Mexico and the United States in April 2009, its epidemiology in Europe during the summer was limited to sporadic and localised outbreaks. Only the United Kingdom experienced widespread transmission declining with school holidays in late July. Using statistical modelling where applicable we explored the following causes that could explain this surprising difference in transmission dynamics: extinction by chance, differences in the susceptibility profile, age distribution of the imported cases, differences in contact patterns, mitigation strategies, school holidays and weather patterns. No single factor was able to explain the differences sufficiently. Hence an additive mixed model was used to model the country-specific weekly estimates of the effective reproductive number using the extinction probability, school holidays and weather patterns as explanatory variables. The average extinction probability, its trend and the trend in absolute humidity were found to be significantly negatively correlated with the effective reproduction number - although they could only explain about 3% of the variability in the model. By comparing the initial epidemiology of influenza A (H1N1) across different European countries, our analysis was able to uncover a possible role for the timing of importations (extinction probability), mixing patterns and the absolute humidity as underlying factors. However, much uncertainty remains. With better information on the role of these epidemiological factors, the control of influenza could be improved.
authors.affiliation: Centre for Infections, Health Protection Agency, London, UK. Stefan.Flasche@hpa.org.uk
authors.forename: Stefan
authors.initials: S
authors.lastname: Flasche
authors.forename: Niel
authors.initials: N
authors.lastname: Hens
authors.forename: Pierre-Yves
authors.initials: PY
authors.lastname: Boëlle
authors.forename: Joël
authors.initials: J
authors.lastname: Mossong
authors.forename: W Marijn
authors.initials: WM
authors.lastname: van Ballegooijen
authors.forename: Baltazar
authors.initials: B
authors.lastname: Nunes
authors.forename: Caterina
authors.initials: C
authors.lastname: Rizzo
authors.forename: Florin
authors.initials: F
authors.lastname: Popovici
authors.forename: Patricia
authors.initials: P
authors.lastname: Santa-Olalla
authors.forename: Frantiska
authors.initials: F
authors.lastname: Hrubá
authors.forename: Kremena
authors.initials: K
authors.lastname: Parmakova
authors.forename: Marc
authors.initials: M
authors.lastname: Baguelin
authors.forename: Albert Jan
authors.initials: AJ
authors.lastname: van Hoek
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Desenclos
authors.forename: Pascale
authors.initials: P
authors.lastname: Bernillon
authors.forename: Amparro Larrauri
authors.initials: AL
authors.lastname: Cámara
authors.forename: Jacco
authors.initials: J
authors.lastname: Wallinga
authors.forename: Tommi
authors.initials: T
authors.lastname: Asikainen
authors.forename: Peter J
authors.initials: PJ
authors.lastname: White
authors.forename: W John
authors.initials: WJ
authors.lastname: Edmunds
mesh_terms: D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D002648:Child; D004196:Disease Outbreaks; D005060:Europe / Q000453:epidemiology; D006693:Holidays; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000302:isolation & purification; D007251:Influenza, Human / Q000175:diagnosis / Q000453:epidemiology* / Q000635:transmission*; D008297:Male; D008875:Middle Aged; D058873:Pandemics; D012044:Regression Analysis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012307:Risk Factors; D012574:Schools; D012621:Seasons; D012919:Social Behavior; D014887:Weather; D055815:Young Adult