Global Mortality Impact of the 1957-1959 Influenza Pandemic

Abstract

Background: Quantitative estimates of the global burden of the 1957 influenza pandemic are lacking. Here we fill this gap by modeling historical mortality statistics.

Methods: We used annual rates of age- and cause-specific deaths to estimate pandemic-related mortality in excess of background levels in 39 countries in Europe, the Asia-Pacific region, and the Americas. We modeled the relationship between excess mortality and development indicators to extrapolate the global burden of the pandemic.

Results: The pandemic-associated excess respiratory mortality rate was 1.9/10,000 population (95% confidence interval [CI], 1.2-2.6 cases/10,000 population) on average during 1957-1959. Excess mortality rates varied 70-fold across countries; Europe and Latin America experienced the lowest and highest rates, respectively. Excess mortality was delayed by 1-2 years in 18 countries (46%). Increases in the mortality rate relative to baseline were greatest in school-aged children and young adults, with no evidence that elderly population was spared from excess mortality. Development indicators were moderate predictors of excess mortality, explaining 35%-77% of the variance. Overall, we attribute 1.1 million excess deaths (95% CI, .7 million-1.5 million excess deaths) globally to the 1957-1959 pandemic.

Conclusions: The global mortality rate of the 1957-1959 influenza pandemic was moderate relative to that of the 1918 pandemic but was approximately 10-fold greater than that of the 2009 pandemic. The impact of the pandemic on mortality was delayed in several countries, pointing to a window of opportunity for vaccination in a future pandemic.

Keywords: development indicators; global disease burden; health indicators; historical studies; models; mortality rates; pandemic influenza; pandemic planning; severity; vital statistics.

Figure 1.

Country-specific influenza-related excess mortality rates from respiratory causes, 1950–1970. Excess mortality rate is calculated as the observed annual mortality rate minus a model-predicted spline baseline fitted to the mortality rate outside the 1957–1959 pandemic period. The 2 black vertical lines highlight mortality attributable to the pandemic period. A, All-age mortality. B, Mortality among individuals aged 15–24 years, the age group with the highest increase in mortality, relative to baseline, during the pandemic period. Mortality rates range from low (yellow) to high (red). Abbreviation: SAR, Special Administrative Region.

Figure 2.

Global maps of pandemic influenza–related mortality rates during the 1957–1959 pandemic period. Estimates are based on 39 countries with available respiratory disease–related mortality data (top panel) and model extrapolation to 122 world countries based on development and geographic indicators (bottom panel).