The shifting demographic landscape of pandemic influenza.
BACKGROUND
As Pandemic (H1N1) 2009 influenza spreads around the globe, it strikes school-age children more often than adults. Although there is some evidence of pre-existing immunity among older adults, this alone may not explain the significant gap in age-specific infection rates.


RESULTS
Based on a retrospective analysis of pandemic strains of influenza from the last century, we show that school-age children typically experience the highest attack rates in primarily naive populations, with the burden shifting to adults during the subsequent season. Using a parsimonious network-based mathematical model which incorporates the changing distribution of contacts in the susceptible population, we demonstrate that new pandemic strains of influenza are expected to shift the epidemiological landscape in exactly this way.


CONCLUSIONS
Our analysis provides a simple demographic explanation for the age bias observed for H1N1/09 attack rates, and suggests that this bias may shift in coming months. These results have significant implications for the allocation of public health resources for H1N1/09 and future influenza pandemics.
Bansal
Shweta
S
Center for Infectious Disease Dynamics, The Pennsylvania State University, University Park, Pennsylvania, United States of America. shweta@sbansal.com
Pourbohloul
Babak
B
Hupert
Nathaniel
N
Grenfell
Bryan
B
Meyers
Lauren Ancel
LA
D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D000368:Aged; D002648:Child; D002675:Child, Preschool; D004196:Disease Outbreaks / Q000517:prevention & control*; D006801:Humans; D017589:Immunization Programs; D007223:Infant; D053118:Influenza A Virus, H1N1 Subtype / Q000276:immunology*; D007252:Influenza Vaccines / Q000008:administration & dosage / Q000276:immunology*; D007251:Influenza, Human / Q000453:epidemiology / Q000517:prevention & control* / Q000821:virology; D008875:Middle Aged; D011157:Population Dynamics; D018570:Risk Assessment; D012621:Seasons; D014481:United States / Q000453:epidemiology; D014505:Urban Population / Q000706:statistics & numerical data; D055815:Young Adult
D007252:Influenza Vaccines