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Analysis of historical data has strongly shaped our understanding of the epidemiology of pandemic influenza and informs analysis of current and future epidemics. Here, the authors analyzed previously unpublished documents from a large household survey of the "Spanish" H1N1 influenza pandemic, conducted in 1918, for the first time quantifying influenza transmissibility at the person-to-person level during that most lethal of pandemics. The authors estimated a low probability of person-to-person transmission relative to comparable estimates from seasonal influenza and other directly transmitted infections but similar to recent estimates from the 2009 H1N1 pandemic. The authors estimated a very low probability of asymptomatic infection, a previously unknown parameter for this pandemic, consistent with an unusually virulent virus. The authors estimated a high frequency of prior immunity that they attributed to a largely unreported influenza epidemic in the spring of 1918 (or perhaps to cross-reactive immunity). Extrapolating from this finding, the authors hypothesize that prior immunity partially protected some populations from the worst of the fall pandemic and helps explain differences in attack rates between populations. Together, these analyses demonstrate that the 1918 influenza virus, though highly virulent, was only moderately transmissible and thus in a modern context would be considered controllable.

Original publication

DOI

10.1093/aje/kwr122

Type

Journal article

Journal

American journal of epidemiology

Publication Date

09/2011

Volume

174

Pages

505 - 514

Addresses

Medical Research Council Centre for Outbreak Modelling and Analysis, Department of Infectious Disease Epidemiology, School of Public Health, Imperial College London, St. Mary’s Campus, London W2 1PG, United Kingdom. c.fraser@imperial.ac.uk

Keywords

Humans, Models, Statistical, History, 20th Century, Family Health, Maryland, Influenza, Human, Pandemics