Mortality displacement

Mortality displacement denotes a temporary increase in the mortality rate (number of deaths) in a given population, also known as excess mortality or an excess mortality rate. It is usually attributable to environmental phenomena such as heat waves, cold spells, epidemics and pandemics, especially influenza pandemics, famine or war.

The COVID-19 pandemic in Spain caused significant excess mortality (expected rate in black, with confidence intervals in gray). Reporting lags lead to undercounting in the latest (rightmost) data.

During heat waves, for instance, there are often additional deaths observed in the population, affecting especially older adults and those who are sick. After some periods with excess mortality, however, there has also been observed a decrease in overall mortality during the subsequent weeks. Such short-term forward shift in mortality rate is also referred to as harvesting effect. The subsequent, compensatory reduction in mortality suggests that the heat wave had affected especially those whose health was already so compromised that they "would have died in the short-term anyway".[1]

Across 24 European countries, mortality data are consolidated by the platform EuroMOMO (European mortality monitoring activity), aiming to detect and measure excess deaths related to seasonal influenza, pandemics and other public health threats. EuroMOMO is hosted and maintained by the Department of Infectious Disease Epidemiology and Prevention of Copenhagen, Denmark.

The study centre at the Statens Serum Institut in Copenhagen publishes a weekly situation report and regular scientific articles. Periods of high excess mortality have also been described for the United States.[2]