One hundred years ago in 1919: New Zealand's birth reduction shock associated with an influenza pandemic

Abstract

AIM:We aimed to conduct a preliminary analysis of any association between the 1918 influenza pandemic and its impact on birth rates in New Zealand. METHODS:Official data covering the period 1910 to 1930 were sourced from multiple New Zealand Yearbooks. Estimates were made of the size of the natality impacts and estimates made of the potential causes. RESULTS:In 1919 there were 3,756 fewer non-Māori and 239 fewer Māori births than the pre-pandemic year of 1917, with these representing reductions in birth rates per 1,000 population of 16.6% and 19.8% respectively. The birth rate reductions in the pandemic year of 1918 (relative to 1917) were less at 8.8% and 6.7% reductions respectively. We estimated the likely major driver of the natality deficit in 1919 was embryonic and fetal loss due to influenza infection in pregnancy. Smaller roles were plausibly played by adult deaths during the pandemic and reduced sexual activity associated with the social turbulence of the peak pandemic months. CONCLUSIONS:The reduction in birth rates in New Zealand in 1918 and especially 1919 are consistent with international data associated with the 1918 influenza pandemic. The relatively higher natality loss for Māori for 1919 is also consistent with other epidemiological data on the unequal burden from this pandemic. Pandemic planning needs to consider ways to prevent such future burdens and associated inequalities. There is also a need to improve on the current low level of routine influenza vaccination in pregnancy so as to minimise fetal loss from seasonal influenza infection.