An estimation of all-cause excess mortality for the United States between March 2020 and February 2022

By Neha MathurReviewed by Lily Ramsey, LLMJun 27 2023

In a recent article published in Science Advances, researchers estimated all-cause excess mortality for the United States (US) between March 2020 and February 2022 to understand the impact of the coronavirus disease 2019 (COVID-19) pandemic.

The study used a Bayesian hierarchical model to determine spatially and temporally granular excess mortality estimates stratified by county and month.

Study: Monthly excess mortality across counties in the United States during the COVID-19 pandemic, March 2020 to February 2022. Image Credit: HTWE/Shutterstock.com

Background

Excess mortality is a more accurate measure of the pandemic's impact, particularly when examining geographic patterns in mortality. This is because all states in the US use different procedures, policies, and resources, which affect the assignment of COVID-19 deaths.

Also, during the pandemic, excess deaths occurred due to multiple factors indirectly related to the pandemic, e.g., people hesitated to visit hospitals for treatment of preexisting health conditions in fear of contracting COVID-19.

About the study

In the present study, researchers retrieved monthly death counts at the county level from the Centers for Disease Control and Prevention (CDC) WONDER online tool. In this way, they found data on death certificates filed in the 50 US states and the District of Columbia.

Next, they converted the number of deaths into rates using the publicly available yearly county-level population estimates from the US Census Bureau.

The researchers then computed excess mortality, i.e., the difference between observed and expected mortality during the COVID-19 pandemic. Within the 2-year study period, they identified four temporal peaks where excess death rates due to COVID-19 surged and dipped steeply.

These were 'Initial, Winter, Delta, and Omicron' peaks spanning March to August 2020, October 2020 to February 2021, August to October 2021, and November 2021 to February 2022.

Results and conclusion

This study estimated excess mortality for 3,127 counties in the US and identified 1,179,024 excess deaths during the first two years of the COVID-19 pandemic, of which 634,830 and 544,194 estimated excess deaths occurred between March 2020 and February 2021, and March 2021 and February 2022, respectively.

Between the first two years of the pandemic, relative excess mortality, i.e., the expected percentage of deaths over (or under) that would have occurred had the pandemic not occurred, decreased in large metros, e.g., Northeastern counties, and increased in nonmetro areas, such as the Southern counties of the US, thus, highlighting the need for investing in rural health.

Notably, during the early pandemic period, COVID-19 caused more deaths in Northeastern counties, and excess mortality in nonmetro areas occurred most markedly during the Delta wave.

The study results could help identify counties where COVID-19-related deaths varied from excess mortality rates. Secondly, these estimates could inform public health workers, community organizations, and residents of the actual impact of the pandemic, which might help increase vaccination uptake or motivate people to take other mitigation measures.

However, most importantly, these results bring to the limelight the policy-level differences across metro-nonmetro regions.

Another intriguing finding of this study is that increased vaccination uptake and coverage failed to reduce excess mortality numbers during the second pandemic year. It also highlighted that federal and state governments did not direct adequate resources to prevent COVID-19 deaths among communities at the highest risk.

Two factors contributed to high rural excess mortality during the second pandemic year. First, vaccination rates in rural areas as of January 2022 were much lower than in urban areas (59% vs. 75%).

Secondly, rural areas had inadequate health infrastructure, which resulted in funding gaps and human resource shortages. Perhaps, racial/ethnic, demographic, and other factors, such as a higher prevalence of comorbidities among rural inhabitants, increased rural excess mortality. 

Nonetheless, the study findings confirmed that the burden of excess mortality in the US shifted from large metropolitan cities in the first pandemic to rural areas in the second year.