In a recent study published within the International Journal of Infectious Diseases, a team of researchers analyzed the mortality in chosen countries during multiple waves of the coronavirus disease 2019 (COVID-19) pandemic in 2020 and 2021 to grasp the evolution of COVID-19-related mortality in accordance with age and sex.

Study: Identifying age- and sex-specific COVID-19 mortality trends over time in six countries. Image Credit: ETAJOE/Shutterstock

Background

The emergence of latest variants of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has resulted in successive waves through the COVID-19 pandemic with varied outcomes in several countries. While broad trends corresponding to a decline in mortality rates have been observed through the second wave after a severe first wave in some European countries corresponding to Italy, detailed information on trends in mortality related to aspects corresponding to age and sex stays largely unclear.

Understanding the demographic structure of the mortality during various waves of the COVID-19 pandemic in several countries will be used to grasp the evolution of COVID-19. Moreover, this information can be useful in evaluating the efficiency of pharmaceutical and non-pharmaceutical mitigation measures in limiting and stopping the spread of the disease.

In regards to the study

In the current study, the researchers obtained age and sex-related COVID-19 mortality data for six countries — Belgium, France, England and Wales, Sweden, Scotland, and the USA (U.S.) — from the database “The Demography of COVID-19 Deaths”. The selection of the countries was based on the official data sources of the countries using comparable definitions for COVID-19-associated mortality. The info covered the pandemic periods between March 2020 and February 2022, apart from the information from France, which was only available until December 2021.

To find out the evolution of COVID-19-associated mortality rates over time, the standardized COVID-19 death rates (SDR) were calculated for every of the countries. The COVID-19 mortality rates were also calculated for specific weeks and seasons for every of the countries based on meteorological definitions of winter (December to February), spring (March to May), summer (June to August), and autumn (September to November).

The male-to-female ratio of age-specific COVID-19 mortality was used to grasp the differences in COVID-19 mortality rates based on sex, which were also calculated in accordance with different seasons for every country.

Results

The outcomes indicated that the intensities and timing of COVID-19-associated mortality vary across the six countries. The summer of 2020 was a period of stabilization for the European countries included within the study but not for the U.S. The authors consider this might be attributed to the more uniform enforcement of strict disease mitigation measures corresponding to lockdowns in European countries in comparison with the U.S. Among the many European countries, Sweden experienced stabilization much later, which might be related to having the least strict COVID-19 mitigation policies and never implementing mandatory lockdowns.

COVID-19-related mortality in European countries was the best through the first two waves, with the following waves of 2021 and early 2022 being milder. The decrease in COVID-19-associated deaths after the second wave might be resulting from a mix of large-scale vaccination efforts, natural immunity from infections through the first and the second wave, the emergence of latest variants with reduced virulence, and the event of improved therapeutical methods.

In contrast, the U.S. experienced a rise in COVID-19-related mortality towards the tip of the summer of 2021 and lengthening into the autumn and winter seasons. These periods, corresponding to the Delta and Omicron variants, had much lower mortality rates within the European countries. The Omicron variant, thought to have reduced virulence despite being highly contagious, caused higher mortality than the Delta variant in Massachusetts, which had high vaccine coverage.

The cumulative COVID-19-related mortality rates were the best for the U.S., which also had high COVID-19-associated deaths among the many younger age groups. Basically, COVID-19-related deaths were the best through the winter months and among the many older age group, but towards the spring of 2021, the COVID-19 mortality rates significantly decreased in Scotland, England and Wales, and the U.S. The authors consider this decrease might be resulting from increased vaccination coverage in these countries.

Evaluation of mortality rates in accordance with sex revealed that men had a better risk of mortality than women for many seasons and age groups, with the sex-based differences being the most important amongst individuals between 50 and 75 years of age.

Conclusions

Overall, the outcomes suggested that COVID-19-associated mortality rates varied across countries and seasons, with further differences based on age and sex. The very best mortality rates were during winter amongst individuals above 75. The European countries experienced periods of stabilization through the summer, which was not observed within the U.S. The U.S. also had high mortality among the many younger age groups.