Influenza in New Zealand Before 1918: A Preliminary Report

Abstract

This paper aims to test the hypothesis of possible fatal immunological reactions to the A/H1N1 virus of the 1918 "Spanish" influenza pandemic caused by previous exposure to the A/H3N8 virus of the 1890–2 "Russian" influenza pandemic. Reconstruction of mortality peaks from influenza and excess pneumonia deaths in New Zealand before 1918 from newspapers and official death records enables comparison with peaks of influenza mortality by age in 1918 from individual death records. Influenza outbreaks in 1885, 1890–2, 1894 and 1898 appear to match mortality peaks for males in the 1918 pandemic. Peaks of female deaths in 1918 correspond to the previous influenza outbreaks of 1887 and 1890–2. The peak mortality for both sexes was in the age-groups 28–32 years. While lending strong support to the hypothesis of fatal immunological reaction derived from early exposure to a different influenza virus, this study also raises more puzzles: given that the A/H1N1 virus of 1918 was exceptionally virulent, why did so few children aged 5–15 die from it? Influenza normally kills only the very young and the very old. And why did twice as many European males than females die in the young-adult age-groups, while Māori males and females died at almost identical rates?