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COVID-19-related mortality shifted toward a relatively younger population during the second year of the pandemic, which contributed to an increase in years of life lost, researchers said.

Although more COVID-related deaths were reported in March to December 2020 compared with the same months in 2021, there was a 7.4% increase in years of life lost -- a measure of premature mortality -- during the second year of the pandemic, with the median age at the time of death due to COVID dropping from 78 in 2020 to 69 in 2021, reported Mark Czeisler, PhD, and Charles Czeisler, PhD, MD, both of Harvard Medical School in Boston.

Overall, years of life lost per COVID death increased by 35.7%, while years of life lost due to any other cause of death did not change by more than 2.2%, they noted in a research letter published in .

"Further investigation should determine the extent to which this downward age shift in COVID-19 mortality is attributable to high early-pandemic COVID-19 death rates among older adults (for example, involving nursing homes and long-term care facilities), relatively higher vaccine coverage and adherence with nonpharmaceutical interventions among older versus younger adults later in the pandemic, age-related risk differences associated with coronavirus variant viruses, or other mechanisms," the researchers wrote.

"Understanding this shift in COVID-19 mortality dynamics could inform prevention and treatment approaches, public policy development, and community measures to minimize future effects of COVID-19," they added.

Over 1 million COVID-related deaths occurred from March 2020 to September 2022 in the U.S. Previous reports have indicated that similar COVID-related death rates occurred from March to December 2020 and from January to October 2021. However, there has been a rise in death rates among younger individuals and a decline among older individuals in 2021 versus 2020, "reflecting excess premature mortality from COVID-19," the authors noted.

In 2021, the CDC reported that COVID-19 was the third leading cause of death. A recently published policy brief from the Institute for Health Metrics and Evaluation suggested that the U.S. will probably not face a major surge in COVID-related deaths this winter, with a model predicting that rates will flatline.

For this study, the researchers used mortality data from March to December 2020 and 2021 from , an integrated system of datasets on public health topics. They also obtained age-specific life expectancies from the 2017 World Population Prospects and the World Health Organization Global Health Estimate, which provided projections for the year 2050 to represent lifespans thought to be achieved by a substantial number of people alive at the time of this analysis.

The top 15 leading causes of death were the same during both time intervals, and accounted for about 80% of all deaths: heart disease, cancer, COVID-19, unintentional injuries, stroke, chronic lower respiratory diseases, Alzheimer's disease, diabetes, chronic liver disease/cirrhosis, kidney disease, influenza/pneumonia, suicide, hypertension, Parkinson's disease, and septicemia.

Across both study intervals, years of life lost linked to most of the leading causes of death were stable. Among three of the four causes of death with greater than 10% changes in death rates during the study intervals, concordant changes were seen in years of life lost.

Considerable increases in both years of life lost (10.5%) and deaths (11%) due to unintentional injuries were observed, which the researchers suggested was partially due to the "record-high drug overdose deaths" that increased by 15% in 2021 -- resulting in nearly 14,000 deaths -- versus 2020.

On the other hand, large decreases in years of life lost and deaths from influenza/pneumonia and Alzheimer's disease were noted:

• Influenza/pneumonia: 14.6% and 16.0%, respectively
• Alzheimer's disease: 12.6% and 14.2%, respectively

The researchers suggested that the decreased deaths rates from Alzheimer's disease, as well as Parkinson's disease, were "perhaps due to early-pandemic increased incidence of each due to misattribution of COVID-19 deaths when there was limited testing and considerable COVID-19-related missed medical care."

They acknowledged several limitations to their study, including the use of provisional 2021 deaths that may have been subject to reporting lags. Since the years of life lost metric compares life expectancy with age at the time of death, they also cautioned that it "should not be used as a measure of a person's potential contributions to society."

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