Primary Submission Category: Mortality
The Delta Wave: An Upper Bound on How COVID-19 Vaccination Shapes Population Mortality Patterns?
Authors: Kaitlyn Berry Andrew Stokes Rafeya Raquib Keeley Morris Elizabeth Wrigley-Field
Presenting Author: Kaitlyn Berry*
Background: Compared to other waves of the COVID-19 pandemic, the Delta wave was unique because it occurred (1) shortly after vaccine availability expanded to the full US adult population, (2) concurrently with initial booster dose recommendations for some groups, (3) before infection-induced immunity became ubiquitous, and (4) during summer rather than winter months.
Aim: We evaluated whether the unique features of the Delta wave resulted in demographically distinctive population-level COVID-19 mortality patterns.
Methods: We used provisional mortality statistics from the National Center for Health Statistics (NCHS) and single-race population estimates from the US Census Bureau to produce age-standardized COVID-19 mortality rates for each month between March 2020 and July 2022 by age and by US Census region. We identified mortality peaks using the month with the highest absolute number of COVID-19 deaths within each wave: initial (April 2020), Alpha (January 2021), Delta (September 2021), and Omicron (January 2022).
Results: Only 14% of Delta peak deaths in the US were among adults aged 85+ compared with 32% of initial, 30% of Alpha, and 24% of Omicron peak deaths. Similarly, the mortality surge during the Delta wave was substantially higher in the South compared with other regions; 62% of all US deaths during the Delta peak occurred in the South, compared to 14% of initial, 40% of Alpha, and 40% of Omicron peak deaths.
Next Steps: We will evaluate state-level factors such as age-specific vaccination rates and monthly temperatures as predictors of the observed mortality patterns during the Delta wave.
Conclusion: Populations that were less vaccinated, including middle-aged adults and people living in the South, experienced greater mortality peaks during the Delta wave than other groups. Because of its temporal proximity to widespread vaccine availability, the Delta wave may represent an upper bound on how COVID-19 vaccination shapes population mortality patterns.