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A comparative study of the 1918-1920 influenza pandemic in Japan, USA and UK: mortality impact and implications for pandemic planning - PubMed

Comparative Study

A comparative study of the 1918-1920 influenza pandemic in Japan, USA and UK: mortality impact and implications for pandemic planning

S A Richard et al. Epidemiol Infect. 2009 Aug.

Abstract

Historical studies of influenza pandemics can provide insight into transmission and mortality patterns, and may aid in planning for a future pandemic. Here, we analyse historical vital statistics and quantify the age-specific mortality patterns associated with the 1918-1920 influenza pandemic in Japan, USA, and UK. All three countries showed highly elevated mortality risk in young adults relative to surrounding non-pandemic years. By contrast, the risk of death was low in the very young and very old. In Japan, the overall mortality impact was not limited to winter 1918-1919, and continued during winter 1919-1920. Mortality impact varied as much as threefold across the 47 Japanese prefectures, and differences in baseline mortality, population demographics, and density explained a small fraction of these variations. Our study highlights important geographical variations in timing and mortality impact of historical pandemics, in particular between the Eastern and Western hemispheres. In a future pandemic, vaccination in one region could save lives even months after the emergence of a pandemic virus in another region.

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Figures

Fig. 1
Fig. 1

Monthly time-series of (a) influenza, (b) pneumonia and influenza, and (c) all-cause mortality rates (——) and predicted Serfling model baseline mortality rates (- - -), Japan, 1915–1923.

Fig. 2
Fig. 2

Comparison of the monthly and annual approaches for estimating excess (a) pneumonia and influenza and (b) all-cause mortality rates/100 population in the 47 Japanese prefectures, during the pandemic period 1918–1920. The monthly approach uses a Serfling seasonal regression and the annual subtraction approach uses rates in surrounding years 1915–1917 and 1921–1923 as baseline. National estimates for Japan are indicated by a solid square (■).

Fig. 3
Fig. 3

Peak month of excess pneumonia and influenza (P&I) mortality, by prefecture and pandemic season. (a) October 1918–May 1919 and (b) December 1919–May 1920. Excess P&I mortality is calculated by the monthly seasonal Serfling approach.

Fig. 4
Fig. 4

Age patterns of excess pneumonia and influenza (P&I) mortality rates in Japan, by year, 1918–1920. Excess mortality estimates are calculated with the annual approach (subtracting mortality in pandemic years 1918–1920 from average baseline mortality in surrounding years 1915–1917 and 1921–1923).

Fig. 5
Fig. 5

(a) Comparison of age-specific excess pneumonia and influenza (P&I) mortality rates during pandemic years 1918–1920 in Japan, UK, and USA. Estimates are calculated using the annual approach. (b) Ratio of P&I mortality during 1918–1920 pandemic years to baseline P&I mortality in 1915–1917 and 1921–1923, for Japan, UK, and USA. Extreme age groups (children aged <5 years and adults aged >55 years) were less affected than young adults, relative to non-pandemic influenza seasons.

Fig. 6
Fig. 6

Percent of excess pneumonia and influenza deaths during 1918–1920 occurring in each year, 1918 (■), 1919 (formula image), and 1920 (□) for Japan, UK, and USA. Excess mortality estimates are based on the annual approach.

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