BACKGROUND: The 1918-1919 A/H1N1 influenza pandemic killed approximately 50 million people worldwide. Historical records suggest that an early pandemic wave struck Europe during the summer of 1918. METHODS: We obtained surveillance data that were compiled weekly, during 1910-1919, in Copenhagen, Denmark; the records included medically treated influenza-like illnesses (ILIs), hospitalizations, and deaths by age. We used a Serfling seasonal regression model to quantify excess morbidity and mortality, and we estimated the reproductive number (R) for the summer, fall, and winter pandemic waves. RESULTS: A large epidemic occurred in Copenhagen during the summer of 1918; the age distribution of deaths was characteristic of the 1918-1919 A/H1N1 pandemic overall. That summer wave accounted for 29%-34% of all excess ILIs and hospitalizations during 1918, whereas the case-fatality rate (0.3%) was many-fold lower than that of the fall wave (2.3%). Similar patterns were observed in 3 other Scandinavian cities. R was substantially higher in summer (2.0-5.4) than in fall (1.2-1.6) in all cities. CONCLUSIONS: The Copenhagen summer wave may have been caused by a precursor A/H1N1 pandemic virus that transmitted efficiently but lacked extreme virulence. The R measured in the summer wave is likely a better approximation of transmissibility in a fully susceptible population and is substantially higher than that found in previous US studies. The summer wave may have provided partial protection against the lethal fall wave.
BACKGROUND: The 1918-1919 A/H1N1 influenza pandemic killed approximately 50 million people worldwide. Historical records suggest that an early pandemic wave struck Europe during the summer of 1918. METHODS: We obtained surveillance data that were compiled weekly, during 1910-1919, in Copenhagen, Denmark; the records included medically treated influenza-like illnesses (ILIs), hospitalizations, and deaths by age. We used a Serfling seasonal regression model to quantify excess morbidity and mortality, and we estimated the reproductive number (R) for the summer, fall, and winter pandemic waves. RESULTS: A large epidemic occurred in Copenhagen during the summer of 1918; the age distribution of deaths was characteristic of the 1918-1919 A/H1N1 pandemic overall. That summer wave accounted for 29%-34% of all excess ILIs and hospitalizations during 1918, whereas the case-fatality rate (0.3%) was many-fold lower than that of the fall wave (2.3%). Similar patterns were observed in 3 other Scandinavian cities. R was substantially higher in summer (2.0-5.4) than in fall (1.2-1.6) in all cities. CONCLUSIONS: The Copenhagen summer wave may have been caused by a precursor A/H1N1 pandemic virus that transmitted efficiently but lacked extreme virulence. The R measured in the summer wave is likely a better approximation of transmissibility in a fully susceptible population and is substantially higher than that found in previous US studies. The summer wave may have provided partial protection against the lethal fall wave.
Authors: Lone Simonsen; Thomas A Reichert; Cecile Viboud; William C Blackwelder; Robert J Taylor; Mark A Miller Journal: Arch Intern Med Date: 2005-02-14
Authors: Zong-Mei Sheng; Daniel S Chertow; Xavier Ambroggio; Sherman McCall; Ronald M Przygodzki; Robert E Cunningham; Olga A Maximova; John C Kash; David M Morens; Jeffery K Taubenberger Journal: Proc Natl Acad Sci U S A Date: 2011-09-19 Impact factor: 11.205
Authors: Shaun A Truelove; Amit S Chitnis; Richard T Heffernan; Amy E Karon; Thomas E Haupt; Jeffrey P Davis Journal: J Infect Dis Date: 2011-01-28 Impact factor: 5.226
Authors: G Chowell; C Viboud; L Simonsen; M A Miller; J Hurtado; G Soto; R Vargas; M A Guzman; M Ulloa; C V Munayco Journal: Vaccine Date: 2011-07-22 Impact factor: 3.641