Conflicting COVID-19 excess mortality estimates

Excess mortality is an important metric summarising COVID-19 disease burden, informing public health policy and future preparedness needs.1 However, separating the deaths that occurred from COVID-19 versus those from all other causes is challenging. Essentially, the unknowns are the counterfactual, should an infection wave not have happened. A solution to this challenge is to estimate expected number of individuals who would have died and compare this with the observed number of deaths. The estimation of expected number of deaths must consider changes in population and seasonal dynamics and be based on an appropriate reference period. The COVID-19 Excess Mortality Collaborators2 present an important study that estimates 18·2 million excess deaths spread across 191 countries and territories in the first 2 years of the COVID-19 pandemic, 2020 and 2021. The authors use an ensemble-based approach to estimate global excess mortality due to data paucity in many countries. Although this global estimate might be broadly correct and serves as an important reminder of the effect of COVID-19, we strongly caution against the over-interpretation of the constituent country estimates. For European countries, we instead recommend the use of EuroMOMO—a standard and coordinated approach for mortality monitoring in Europe. EuroMOMO estimates expected excess mortality, correcting for delay in registration and changes in population and seasonality during a 5-year reference period.3 EuroMOMO excess mortality estimates include both surplus and deficit mortality, with deficit mortality expected under stringent control restrictions. Whether the COVID-19 Excess Mortality Collaborators2 consider both surplus and deficit mortality is unclear.