key: cord-0818561-83nc9qis
authors: Ghio, Daniela; Acosta, Enrique; Fisman, David; Noymer, Andrew; Stilianakis, Nikolaos I.; Assche, Simona Bignami-Van
title: Population Health and COVID-19 in Canada: a Demographic Comparative Perspective
date: 2021-09-22
journal: Can Stud Popul
DOI: 10.1007/s42650-021-00057-9
sha: fd77c9ec74469485f81cb38a7901b40f7a95eaaa
doc_id: 818561
cord_uid: 83nc9qis

nan

thus attempt to put Canada's pandemic experience in context. Recent demographic research has focused on excess mortality attributable to COVID-19 (for instance: Garcia-Guerrrero et al., and Decarie and Michaud, in this issue) , which is now considered to best represent the full impact of the pandemic since it includes both total COVID-19 mortality as well as mortality indirectly related to the disease (WHO, 2021) . Current global estimates of COVID-19 excess mortality are close to 3 million deaths, 1.2 million more than the official count of COVID-19 deaths. 1 The region of the Americas (that includes Canada, the USA, and Mexico) 2 accounts for 1.34-1.46 million excess deaths attributable to COVID-19, a figure slightly higher than the corresponding one for the European region (1.11-1.21 million excess deaths). 3 In Canada, the number of excess deaths is estimated at 18,511 between March 2020 and April 2021 (Statistics Canada, 2021a). However, Canada lags extremely behind other high-income countries in mortality and cause-of-death reporting, which is of provincial responsibility and largely paper-based (Décarie and Michaud, this issue). For instance, as of early June 2021, the province of Manitoba had not yet finished tallying the overall death count for 2020 (Statistics Canada, 2021a) , and cause-of-death data was complete only until February 2020-before the pandemic even begun (Moriarty et al., 2021) .

Given data limitations for the accurate estimation of excess mortality, comparisons of the case fatality risk (CFR), that is, the ratio of reported deaths to diagnosed infections of severe acute respiratory syndrome coronavirus (SARS-CoV-2), are useful to put the Canadian pandemic experience in context. The CFR has been one of the main indicators used for developing mitigation strategies (including vaccination) and evaluating their effectiveness across countries over the course of the pandemic. International comparisons of COVID-19 CFR have also become important to assess the health burden associated with SARS-CoV-2 mutations.

Estimates of COVID-19 CFR have varied substantially across countries over the course of the pandemic (Rajgor et al., 2020) . In part, as studies of other emerging pathogens like Ebola and SARS have shown (Ghani et al., 2005; Lipsitch et al., 2015; Wu et al., 2020) ; this is due to the delay between symptoms onset, diagnosis, and death or recovery. In the case of COVID-19, an additional source of bias is that a significant proportion of SARS-CoV-2 infections are mild or remain asymptomatic, 1 Only 16 of the WHO's 106 member states have sufficient data to calculate excess mortality empirically. Several demographers (including Noymer, Acosta and Bignami) are currently involved in the WHO/UN Technical Advisory Group (TAG), whose work informs mortality assessment underlying estimated presented in the WHO's 2021 World Statistics Report (WHO, 2021) and the UN's 2021 World Population Prospects (to be released in 2022). It is worth noting that, for many countries (representing most of the world's population), there will never be direct, vital-registration based measures of COVID-19 mortality and excess mortality, however. and thus avoid detection (Li et al., 2020) . At the same time, COVID-19 severity increases with age (Goldstein & Lee, 2020; Green et al, 2020; Guilmoto, 2020) , and thus, older individuals are over-represented in epidemiological data (Fisman et al., 2020) . These issues are compounded by the fact that countries vary in recording COVID-19 as the cause of death, and accurate cause-of-death data remains incomplete while the pandemic is still unfolding (Garcia et al., 2021; Goldstein & Lee, 2020) . Dudel et al. (2020) have shown that the age structure of confirmed SARS-CoV-2 infections is an important source of bias in international comparisons of the CFR, as it can account for up to two-thirds of the observed variation in the CFR across countries. To remove the above-mentioned biases in CFR comparisons, demographic studies have followed a classic approach in mortality analysis and relied on direct standardization by age of the CFR (Dowd et al., 2020; Goldstein & Lee, 2020; Green et al., 2020; Guilmoto, 2020; Sudharsanan et al., 2020) . The main disadvantage of age-standardized CFRs is that they vary depending on the choice of the standard population. We thus exploit another demographic tool and compare COVID-19 mortality in Canada and a selected number of countries with a synthetic indicator that removes the effect of differential case ascertainment by age without relying on standardization (Bignami & Ghio, 2020 . 4 Comparable data on cases and deaths by age are taken from COVerAGE-DB, one of the few existing databases of official counts of COVID-19 cases and deaths that are standardized and made accessible in harmonized age groups .

To avoid spurious comparisons because of the different pace of COVID-19 vaccination starting in January 2021, we limit our focus to the period ending on February 27, 2021, which captures the first and second pandemic wave in the selected countries. As it can be seen in Table 1 , the first wave (begun in February 2020 and considered concluded by the end of June 2020) has been, in absolute terms, smaller and less fatal than the second wave (begun in Fall 2020) in all countries considered. During the second wave, the table shows that the number of confirmed COVID-19 cases increased approximately geometrically, whereas the number of COVID-19-related deaths increased arithmetically. This is predominantly due to expanded testing capacity as the pandemic progressed and also to the younger age profile of COVID-19-related infections and deaths during the second wave compared to the first (Fig. 1) .

Once differential case ascertainment by age across countries and between pandemic waves is taken into account, overall differences in COVID-19 fatality across countries are less stark than suggested by the crude CFR, especially for the first pandemic wave. Overall, Canada ranks just below Sweden in terms of COVID-19 fatality at the end of the second wave (Fig. 2) , ahead of the USA and Italy. Canada was also among the top three countries where COVID-19 had been most fatal during the first wave, the other two being Italy and Sweden. The age pattern of COVID-19 fatality is not unique, however. In some countries (e.g., Italy), it results from the highest age-specific CFRs between age 50 and 70, whereas in others (notably Sweden and Canada) from the highest age-specific CFRs above age 70. Canada's ranking is noteworthy since most infections and deaths have been concentrated in the provinces of Québec and Ontario in both pandemic waves (Bignami, in this issue) . Note: 2: February 27, 2021. Age-specific case-fatality risk at age x = number of COVerAge-DB , except Canada (StaƟsƟcs Canada, 2021 a,b).

COVID-19-related deaths at age x/number of COVID-19 cases at age x. Source: 

A demographic adjustment to improve measurement of COVID-19 severity at the developing stage of the pandemic

Comparing COVID-19 fatality across countries: A synthetic demographic measure

Sex difference and smoking predisposition in patients with COVID-19

Demographic science aids in understanding the spread and fatality rates of COVID-19

SyntheƟc casefatality risk (SCFR) calculated as described in Bignami and Ghio (2020). The SCFR measures the average number of deaths per 100 COVID-19 cases. Source: COVerAge-DB (Riffe, et al., 2021), except Canada (StaƟsƟcs Canada, 2021 a,b). structure and age-specific fatality

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Sex differences in the mortality rate for coronavirus disease 2019 compared to other causes of death

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The confounded case fatality rates (CFR) for COVID-19 hide more than they reveal-a comparison of age-specific and age-adjusted CFRs between seven countries

COVID-19 death rates by age and sex and the resulting mortality vulnerability of countries and regions in the world

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Potential biases in estimating absolute and relative case-fatality risks during outbreaks

Population age structure only partially explains the large number of COVID-19 deaths at the oldest ages

Excess all-cause mortality during the COVID-19 epidemic in Canada

The many estimates of COVID-19 case fatality rate

Data resource profile: COVerAGE-DB: A global demographic database of COVID-19 cases and deaths

Considering how biological sex impacts immune responses and COVID-19 outcomes

The Daily

Preliminary dataset on confirmed cases of COVID-19, Public Health Agency of Canada

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World Health Statistics 2021. World Health Organization

Estimating clinical severity of COVID-19 from the transmission dynamics in Wuhan, China