Impact of Population Growth and Aging on Estimates of Excess U.S. Deaths During the COVID-19 Pandemic, March to August 2020

“Studies of excess deaths in the United States, as well as analyses published by the media, have calculated the absolute excess number of deaths by using data from the Centers for Disease Control and Prevention (CDC) on total deaths, by week, in 2020 compared with deaths during the same week in recent years (2014/2015 to 2019). These estimates did not account for population changes during the comparison period, although the U.S. population is in the midst of a major transition driven by aging of the Baby Boomers (that is, the 1945 to 1965 birth cohorts). Of importance, the population aged 65 years and older grew by a third in the past decade. Here, we use additional data released by the CDC on age at death to show the importance of accounting for the shifting age structure and population size when estimating the total number of excess deaths in the United States during the COVID-19 pandemic.

[..] Age-specific excess deaths from March through August 2020 were estimated in 2 ways. First, the average annual number of deaths in each month in 2015 to 2019 was subtracted from the observed number of deaths in 2020 in each age group (that is, no adjustment was made for population growth and aging). Second, the expected number of deaths in 2020 was estimated with direct standardization by applying the age-specific death rate in 2015 to 2019 to population counts in 2020, by age and month, and then subtracted from the observed number of deaths in 2020 (that is, with adjustment for population growth and aging). Expected deaths are the number of deaths that would have occurred in 2020 if age-specific death rates were the same as in 2015 to 2019. Excess deaths were estimated by cause of death, age group (24 to 64 years and ≥65 years), and month. Non–COVID-19 deaths were estimated by subtracting COVID-19 deaths from total excess death estimates. Because COVID-19 deaths occurred only in 2020, estimates of the number of COVID-19 deaths are not affected by temporal changes in population size or age structure. All estimates were rounded to the nearest 100 deaths.

[..] The U.S. Census Bureau estimates that the total U.S. population in 2020 is 5.22 million persons larger than the average size of the 2015 to 2019 population, including an increase of 5.04 million aged 65 years and older (10% increase), and that it decreased in some younger age groups. Annual deaths have also increased, such that from 2015 to 2019, deaths in each year exceeded the average number of deaths from the preceding 5 years by 114 000 to 163 000 deaths.

[..] Between 1 March and 31 August 2020, 1 671 400 deaths were registered in the United States, according to provisional CDC data. Death rates per month in 2020 were higher than in 2015 to 2019 across all groups aged 15 years and older, with the largest absolute increases in the oldest age groups (75 to 84 years: +44.3 per 100 000 person-months; ≥85 years: +138.7 per 100 000 person-months). An average of 1 370 000 deaths were reported during March to August 2015 to 2019, for a crude excess of 301 400 deaths, including 173 300 due to COVID-19 and 128 100 (43%) due to non–COVID-19 causes. However, if the age-specific death rate in 2020 were the same as in 2015 to 2019, an additional 83 500 deaths would have occurred in March to August 2020 because of changes in population size and age composition alone, for a total of 1 453 500 expected deaths. After accounting for these population changes, we estimate that 217 900 excess deaths occurred during this 6-month period in 2020. The number of COVID-19 deaths did not change, but the number of deaths from other causes declined to 44 600 (20% of the 217 900 excess deaths). Most of the difference between the 2 estimates of non–COVID-19 deaths (−82,100) occurred in the groups aged 65 years and older, in which population growth has been greatest and death rates are highest.

[..] After the growth and aging of the U.S. population were taken into account, the 2020 COVID-19 pandemic resulted in an estimated 218 000 excess deaths between March and August, 80% (n = 173 000) of which had COVID-19 as the underlying cause. Most of the 45 000 non–COVID-19 excess deaths occurred during April, July, and August, with far fewer in March, May, and June. Although this is a substantial number of excess deaths in a 6-month period, it is 83 000 fewer than would have been estimated if we had failed to account for population growth and aging.”

Full article, Shiels MS, Almeida JS, Garcia-Closas M et al. Annals of Internal Medicine, 2020.12.15