Estimating excess mortality due to the COVID-19 pandemic: a systematic analysis of COVID-19-related mortality, 2020–21

Abstract

Mortality  statistics  are  fundamental  to  public  health  decision  making.  Mortality  varies  by  time  and  location,  and  its  measurement  is  affected  by  well  known  biases  that  have  been  exacerbated  during  the  COVID-19 pandemic. This paper aims to estimate excess mortality from the COVID-19 pandemic in 191 countries and territories, and 252 subnational units for selected countries, from Jan 1, 2020, to Dec 31, 2021.

Methods

All-cause  mortality  reports  were  collected  for  74  countries  and  territories  and  266  subnational  locations  (including 31  locations  in  low-income  and  middle-income  countries)  that  had  reported  either  weekly  or  monthly  deaths  from  all  causes  during  the  pandemic  in  2020  and  2021,  and  for  up  to  11  year  previously.  In  addition,  we  obtained excess mortality data for 12 states in India. Excess mortality over time was calculated as observed mortality, after  excluding  data  from  periods  affected  by  late  registration  and  anomalies  such  as  heat  waves,  minus  expected  mortality. Six models were used to estimate expected mortality; final estimates of expected mortality were based on an ensemble of these models. Ensemble weights were based on root mean squared errors derived from an out-of-sample predictive validity test. As mortality records are incomplete worldwide, we built a statistical model that predicted the excess mortality rate for locations and periods where all-cause mortality data were not available. We used least absolute shrinkage and selection operator (LASSO) regression as a variable selection mechanism and selected 15 covariates, including  both  covariates  pertaining  to  the  COVID-19  pandemic,  such  as  seroprevalence,  and  to  background  population  health  metrics,  such  as  the  Healthcare  Access  and  Quality  Index,  with  direction  of  effects  on  excess  mortality concordant with a meta-analysis by the US Centers for Disease Control and Prevention. With the selected best model, we ran a prediction process using 100 draws for each covariate and 100 draws of estimated coefficients and  residuals,  estimated  from  the  regressions  run  at  the  draw  level  using  draw-level  input  data  on  both  excess  mortality and covariates. Mean values and 95% uncertainty intervals were then generated at national, regional, and global levels. Out-of-sample predictive validity testing was done on the basis of our final model specification.

Findings

Although reported COVID-19 deaths between Jan 1, 2020, and Dec 31, 2021, totalled 5·94 million worldwide, we estimate that 18·2 million (95% uncertainty interval 17·1–19·6) people died worldwide because of the COVID-19 pandemic (as measured by excess mortality) over that period. The global all-age rate of excess mortality due to the COVID-19 pandemic was 120·3 deaths (113·1–129·3) per  100 000 of the population, and excess mortality rate exceeded 300 deaths per 100 000 of the population in 21 countries. The number of excess deaths due to COVID-19 was largest in the regions of south Asia, north Africa and the Middle East, and eastern Europe. At the country level, the highest numbers of cumulative excess deaths due to COVID-19 were estimated in India (4·07 million [3·71–4·36]), the USA (1·13  million  [1·08–1·18]),  Russia  (1·07  million  [1·06–1·08]),Mexico  (798  000  [741 000–867 000]),  Brazil  (792 000[730 000–847 000]),  Indonesia  (736 000  [594 000–955 000]),  and  Pakistan  (664 000  [498 000–847 000]).  Among  these  countries,   the   excess   mortality   rate   was   highest   in   Russia   (374·6   deaths   [369·7–378·4]   per   100 000)   and   Mexico (325·1 [301·6–353·3] per  100 000), and was similar in Brazil (186·9 [172·2–199·8] per  100 000) and the USA (179·3 [170·7–187·5] per  100 000).

Interpretation

The full impact of the pandemic has been much greater than what is indicated by reported deaths due to  COVID-19  alone.  Strengthening  death  registration  systems  around  the  world,  long  understood  to  be  crucial  to  global  public  health  strategy,  is  necessary  for  improved  monitoring  of  this  pandemic  and  future  pandemics.  In  addition, further research is warranted to help distinguish the proportion of excess mortality that was directly caused by SARS-CoV-2 infection and the changes in causes of death as an indirect consequence of the pandemic.