Compare COVID-19 deaths between countries using all-cause excess mortality, says study

Inconsistent criteria for attributing a death to COVID-19, in age/comorbidity structures and in policies for identifying asymptomatic people with SARS-CoV-2 infection, are the main cause of between-country discrepancy of mortality metrics for the dreaded disease, according to a study.

“All-cause excess mortality is recommended as a more reliable metric for comparing countries,” the researchers said.

Data from open databases (primarily Our World in Data) were used to compare and interpret trends of mortality among 11 Western countries, namely Austria, Belgium, Canada, France, Germany, Italy, the Netherlands, Spain, Sweden, the UK, and the US.

The researchers also compared between-country trends in mortality rate and case-fatality (both including deaths for COVID-19 as numerator and therefore labeled as COVID-19 mortality metrics) and all-cause excess mortality (ie, observed deaths during the epidemic compared with those expected based on mortality in the same periods of previous years).

Belgium ranked first in death from COVID-19, potentially due to the broadest criterion for attributing a death to COVID-19, but it did not rank first for all-cause excess mortality. On the other hand, Italy, Spain, and the UK reported lower COVID-19 mortality, possible due to the narrower definitions for a COVID-19 death, but had higher all-cause excess mortality than Belgium. [J Hypertens 2021;39:856-860]

Notably, Germany and Austria consistently exhibited the lowest rates of COVID-19 mortality, case-fatality, and all-cause excess mortality.

The analysis revealed two groups of countries: the first group, which included Belgium, France, Italy, the Netherlands, Spain, and the UK, exceeded or nearly reached a twofold greater value than expected, mostly during the first epidemic wave; the second group, which included Austria, Canada, Germany, Sweden, and the US, never exceeded a 1.5-fold greater value than expected.

“Although these figures quantify overall differences in disease between countries, excess mortality has been shown to differ within countries, varying according to demographic parameters such as age, clinical parameters such as comorbidities, and social parameters such as specific features of different ethnic groups,” the researchers said. [Eurohealth 2020;26:45-50; PLoS Med 2020;17:e1003321; Lancet 2020;23:1004040]

Comparisons of COVID-19 deaths between countries and over time were deemed poorly informative and potentially biased due to two types of reasons: the numerator of the COVID-19 mortality rate (ie, the comparability of the criteria applied when attributing a death to COVID-19) and the denominator of the mortality rate (ie, the composition of the population that the COVID-19 data were derived from).

“With regard to the numerator of the COVID-19 mortality rate, according to the [World Health Organization], a death due to COVID-19 is ‘a death resulting from a clinically compatible illness, in a probable or confirmed COVID-19 case, unless there is a clear alternative cause of death that cannot be related to COVID–19 disease’,” the researchers said. [https://www.who.int/classifications/icd/Guidelines_Cause_of_Death_COVID-19-20200420-EN.pdf]

“With regard to the denominator of the COVID-19 mortality rate, distinction should be made between mortality rate and case-fatality as respectively representing denominators of the entire population and cases with reported COVID-19 infection,” they added.

No lack of data culture exists at present, but a “great cultural effort” has to be done to reintroduce a culture of “information supporting decisions” or evidence-based decision-making together with that of data culture, according to the researchers.

“Therefore, other than placing high priority on timely collection of mortality data in the future, educational efforts to introduce (or reintroduce) good practice with regard to correctly interpreting such data should be taken into account,” they said.