1. COVID-19 caused the second-largest infection-related mortality disaster in Switzerland, Sweden, and Spain.
2. The study was limited by the use of historical vital statistics from various European countries.
Evidence Rating Level: 2 (Good)
Study Rundown: Excess mortality compares expected and observed values and ideally captures what would have happened based on extrapolation of observations from previous years. Excess mortality is being increasingly used to quantify the overall impact of COVID-19 in 2020, but there is a gap in knowledge as to comparing pandemics between countries over longer periods based on uniformly structured data sets analyzed with a common approach. This study found that in 2020, the COVID-19 pandemic led to the second-largest infection-related mortality disaster in three European countries since the beginning of the 20th century. This study was limited by minor completeness issues of historical vital statistics before the beginning of the 20th century. Nevertheless, these study’s findings are significant, as they demonstrate that COVID-19’s overall mortality impact in 2020 in Switzerland, Sweden, and Spain led to the second-largest mortality disaster driven by a viral infection in more than a century, second only to the 1918 influenza pandemic.
In-Depth [observational study]: This observational study measured a continuous series of recorded deaths from all causes by month from the earliest available year for the three countries studied: 1877 for Switzerland, 1851 for Sweden, and 1908 for Spain. These countries were included because they were militarily neutral and not involved in combat during the 2 world wars, were not simultaneously affected by war-related excess mortality, and had not been affected by significant changes in their territory. Other countries were excluded based on these criteria as well. The primary outcome measure was to use annual age group-specific death and total population counts to estimate the expected number of deaths in a pandemic year for a non-pandemic scenario and the difference in observed and expected deaths aggregated over the year. Outcomes in the primary analysis were assessed via a Bayesian model and statistical inference was conducted with Hamiltonian Monte Carlo techniques. Based on the analysis, in 2020, the number of excess deaths recorded per 100,000 people was 100 (95% credible interval [CrI], 60 to 135) for Switzerland, 75 (95% CrI, 40 to 105) for Sweden, and 155 (95% CrI, 110 to 195) for Spain. In 1918, excess mortality was 6 to 7 times higher per 100,000 persons compared to 2020. However, in all 3 countries, the peaks of monthly excess mortality in 2020 were greater than most monthly excess mortality since 1918, including many previous peaks due to seasonal influenza and heatwaves. Overall, this study demonstrated that COVID-19’s overall impact in 2020 in Sweden, Switzerland, and Spain led to the second-largest mortality disaster driven by a viral infection in more than 100 years, second only to the 1918 influenza pandemic, though COVID-19’s effects and impact on mortality are still ongoing.
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