Estimating global and country-specific excess mortality during the COVID-19 pandemic – World Health Organization

Overview

Estimating the true mortality burden of COVID-19 for everycountry in the world is a difficult, but crucial, public health endeavor.Attributing deaths, direct or indirect, to COVID-19 is problematic. A moreattainable target is the excess deaths, the number of deaths in a particularperiod, relative to that expected during normal times, and we estimatethis for all countries on a monthly time scale for 2020 and 2021. The excessmortality requires two numbers, the total deaths and the expected deaths, butthe former is unavailable for many countries, and so modeling is required forthese countries, and the expected deaths are based on historic data and wedevelop a model for producing expected estimates for all countries.We allowfor uncertainty in the modeled expected numbers when calculating the excess.We describe the methods that were developed to produce World HealthOrganization (WHO) excess death estimates. To achieve both interpretabilityand transparency we developed a relatively simple overdispersed Poissoncount framework, within which the various data types can be modeled. Weuse data from countries with national monthly data to build a predictive log-linearregression model with time-varying coefficients for countries withoutdata. For a number of countries, subnational data only are available, and weconstruct a multinomial model for such data, based on the assumption thatthe fractions of deaths in specific sub-regions remain approximately constantover time. Our inferential approach is Bayesian, with the covariate predictivemodel being implemented in the fast and accurate INLA software. Thesubnational modeling was carried out using MCMC in Stan or in some nonstandarddata situations, using our own MCMC code. Based on our modeling,the 95% interval estimate for global excess mortality, over 20202021,is 13.316.6 million.

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Estimating global and country-specific excess mortality during the COVID-19 pandemic - World Health Organization