First two years of the COVID-19 pandemic caused excess deaths in the United States

In a recent study posted to the medRxiv* pre-print server, researchers used seasonal autoregressive integrated moving averages (sARIMA) to estimate excess mortality, defined as the difference between the number of observed and expected deaths in the United States (US).

The scientists calculated excess mortality stratified by age, region, gender, and ethnicity during the first two years of the coronavirus disease 2019 (COVID-19) pandemic.

Background

A detailed evaluation of all-cause excess mortality, defined as the difference between the number of observed and expected deaths in the US during the first two years of the COVID-19 pandemic, stratified by age, sex, region, and ethnicity can provide an accurate representation of the population-level effects of the pandemic.

About the study

In the present study, researchers retrieved the Centers for Disease Control and Prevention (CDC) and National Center for Health Statistics (NCHS) data from 2014-2022 to estimate excess mortality in the US  during the first two years of the pandemic between March 1, 2020, and February 28, 2022. Additionally, they applied sARIMA to monthly mortality data between January 2015 and February 2020 to project the monthly number of expected deaths for March 1, 2020-February 28, 2022, normalizing the difference in days for each month.

The researchers divided the two-year study period into six periods before determining expected deaths for each of the four US Census Bureaus by summing estimates from the nine US Census Divisions, determined by age and gender subgroup projections. Next, they added 72 components to create US-level estimates. For the ethnicity analysis, adequate data for monthly projects were available for non-Hispanic Black, non-Hispanic White, and Hispanic populations.

For US-level ethnicity estimates, they summed 24 parts, with eight sARIMAs for each of the three ethnicity groups, in the age bands zero to 17, 18 to 49, 50 to 64, and ≥65 by gender. The team modeled state-level estimates reflecting the summation of age-specific component models for 37 states and inadequate age-specific data without age stratification for 14 states.

The researchers continuously corrected the monthly expected deaths to reflect the decrease in population due to cumulative pandemic-associated excess deaths. Further, they reported the raw number of excess deaths, observed-to-expected ratios, incident rates per 100,000 person-periods for excess mortality, the crude rate, and COVID-19-specific mortality incident rates.

Study findings

The study highlighted the distinct regional and age-specific changes in all-cause excess mortality in the US during the first two years of the COVID-19 pandemic. Regarding age-related effects, excess mortality from the ≥65-year-old demographic first transiently decreased. However, their share of deaths soon became the majority again, as younger groups began to receive vaccinations. Another likely reason was that the Delta variant decreased vaccine effectiveness against severe disease in older populations. Only during April and May 2021, adults ages 50-64 years i.e., a non-geriatric demographic, represented most of the excess mortality during the pandemic.

Region-wise, the South suffered the most mortality burden from the pandemic, with 507,454 excess deaths, representing 22% higher than expected, than the Midwest, which had 17% higher than expected excess deaths. Indeed, the share of the South increased later in the pandemic period. Although the Northeast suffered more early in the pandemic, with a 20% increase in excess mortality, the South exceeded the Northeast, especially as vaccines became available, as also observed during national surveys evaluating vaccine adoption data.

The study tracked the excess mortality toll with the infection waves, unbiased by labels of the cause of death. Thus, the results indicated that the excess deaths were related to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and were not a by-product of societal changes. Unfortunately, the pandemic also worsened the impact of structural racism in the US. The excess deaths were higher than the historical death rates observed in these groups, with the excess death rate of 458.3 per 100,000 in Black people and 298 per 100,000 in Hispanic people.

Conclusions

In summary, the study results showed a more than 20% increase in all-cause deaths in the United States, resulting in nearly 1.2 million more deaths than expected in the first two years of the COVID-19 pandemic. Some age and ethnic groups suffered disproportionately; for instance, the young people, non-Hispanic Black and Hispanic people, and those living in the South showed a higher deviation in all-cause deaths relative to the historic US standards. Therefore, future pandemic planning should focus on mitigating the overall harm due to COVID-19 by specifically addressing populations at the highest risk.

*Important notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Written by

Neha Mathur

Neha is a digital marketing professional based in Gurugram, India. She has a Master’s degree from the University of Rajasthan with a specialization in Biotechnology in 2008. She has experience in pre-clinical research as part of her research project in The Department of Toxicology at the prestigious Central Drug Research Institute (CDRI), Lucknow, India. She also holds a certification in C++ programming.