Deaths Associated with Influenza Pandemic of 1918–19, Japan

Siddharth Chandra

Author affiliation: Michigan State University, East Lansing, Michigan, USA

Abstract

Current estimates of deaths from the influenza pandemic of 1918–19 in Japan are based on vital records and range from 257,000 to 481,000. The resulting crude death rate range of 0.47%–0.88% is considerably lower than parallel and conservative worldwide estimates of 1.66%–2.77%. Because the accuracy of vital registration records for early 20th century Asia is questionable, to calculate the percentage of the population who died from the pandemic, we used alternative prefecture-level population count data for Japan in combination with estimation methods for panel data that were not available to earlier demographers. Our population loss estimates of 1.97–2.02 million are appreciably higher than the standing estimates, and they yield a crude rate of population loss of 3.62%–3.71%. This rate resolves a major puzzle about the pandemic by indicating that the experience of Japan was similar to that of other parts of Asia.

The influenza pandemic of 1918–19 caused unprecedented devastation (1); worldwide, it is estimated to have taken 25–100 million lives (2,3), exceeding the combined death toll of both world wars. One of the strangest aspects of the currently held wisdom about the pandemic is the curiously low death rate attributed to Japan compared with other countries in Asia. Official records for Japan put the death toll at 257,363 persons (4), resulting in a crude influenza-attributable death rate of 0.47%. Patterson and Pyle (2) reported 350,000 deaths, and Johnson and Mueller (3) cited a figure from Palmer and Rice (5) of 388,000 deaths. Given Japan’s population of >54 million at the time (6), the influenza-attributable mortality rates (0.64%–0.71%) are remarkably low by Asian standards, although they are similar to the rates calculated for the United States, Canada, and western Europe (0.65%, 0.61%, and ≈0.48%, respectively) (3). Patterson and Pyle’s (2) conservative estimate of a global rate of 1.66% and Johnson and Mueller’s (3) substantial upward revision of that percentage to 2.77% suggest that the estimates for Japan, which are less than one quarter of the latter estimate, merit closer scrutiny. Although the epidemiologic approach used by Richard et al., which also uses death statistics reported by the Japanese health authorities, raises the estimate to 481,000 (or 0.88% of the population at the time) (7), even this estimate is extraordinarily lower than estimates from other parts of Asia.
As Taeuber argued in her classic book, The Population of Japan, Japan occupies a special place in demography (8). Worldwide it remains one of the largest economies (third in 2011) and one of the most populous countries (tenth in 2011). Yet, surprisingly, substantial knowledge gaps remain with regard to the influenza pandemic of 1918–19 in Japan, rendering it “a strangely neglected episode in modern Japanese history” (4, p. 389). For example, a search of Taeuber’s work for the term “influenza” revealed only 1 mention of the influenza epidemic of 1918, in the context of speculation that it “may have led to reduced conceptions” (8, p. 233).
The few scholars who have studied the influenza pandemic in Japan have approached it from 1 of 3 broad perspectives: historical, epidemiologic, or demographic. The historical approach is exemplified by the works of Palmer and Rice, which provide a qualitative contextualization of aspects of the pandemic and its management in Japan (4,5,9,10). A second line of research is epidemiologic, within which 2 broad goals are pursued. The first goal is to produce estimates of major epidemiologic characteristics of the virus (11–13), and the second goal is to produce epidemiology-based estimates of mortality rates from the pandemic (7). The demographic approach is exemplified by Morita, Okazaki, Taeuber, and Yasukawa and Hirooka (8,14–16). Although these studies emphasize broader patterns of population growth in Japan, a few address the question of death rates during the pandemic. For example, Yasukawa and Hirooka (16) relied directly on official death statistics, including those from the pandemic, to produce estimates of the population in early 20th-century Japan. Unfortunately, the quantitative literature seems to have more or less accepted the official vital statistics on disease-specific deaths, feeding them (and therefore their inaccuracies) into otherwise technically refined estimates of population and population growth.
A common characteristic of the above studies is their heavy reliance on official vital and health statistics of the time. Such data are widely recognized by demographers as being plagued by the often-severe problem of underreporting. Indeed, according to Johnson and Mueller, “it is generally accepted that recorded statistics of influenza morbidity and mortality are likely to be a significant understatement” (3, p. 108). For India, Davis estimated that the “amount of underregistration certainly exceeds 30 per cent at all times, and is probably nearer 50 per cent” (17, p. 34). For Indonesia, Gooszen advised that such data “should be regarded with a good deal of caution” (18, p. 32), and Nitisastro opined that “for the system of registering deaths, the quality of the results was poor” (19, p. 101). Japan is no exception to this pattern. According to Mosk, “we do not have a trustworthy picture of what happened to vital rates in the Tokugawa period…. The same can be said for the Meiji period” (20, p. 658), and Taeuber’s assessment was that “the critical question is the accuracy of the records of vital events” (8, p. 50). The uncharacteristically low estimates of deaths from influenza in Japan provide a strong rationale for cross-checking the findings in the manner of Davis’ classic study of India (17).
We therefore used recently developed statistical methods to estimate the loss of population in Japan from the influenza pandemic of 1918–19. We adopted an approach that intentionally avoids heavy reliance on vital registration data and is based instead on population count data for Japan of that period. By applying data for multiple prefectures over time to prefecture-level population statistics, we estimated population loss from the pandemic to be the difference between expected population (using the prepandemic trajectory) and observed population (using the postpandemic trajectory) (17,21,22). The new estimates are appreciably higher than the earlier estimates, bringing Japan’s pandemic experience in line with that of other parts of Asia and resolving a major puzzle in the epidemiology of the 1918–19 pandemic.