Transmissibility of influenza during the 21st-century epidemics, Spain, influenza seasons 2001/02 to 2017/18

Individuals under 15 years of age presented higher transmissibility, especially in the 2009 influenza A(H1N1) pandemic. Seasons with dominance/co-dominance of influenza A(H3N2) virus presented high intensities in older adults.In 12 seasons, the epidemic started between week 50 and week 3. Epidemics started earlier in individuals under 15 years of age than in those over 64 years when influenza B virus circulated as dominant/co-dominant. The average time from start to peak was 4.3 weeks and the average epidemic length was 8.7 weeks.  Eurosurveillance

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