The COVID-19 pandemic significantly impacted the U.S. population through increased mortality, decreased fertility rates, and reduced migration. While individual studies have examined these effects separately, this research aims to quantify their combined influence on the U.S. population structure until 2060. Understanding this joint impact is crucial for effective long-term planning in areas such as healthcare, childcare, housing, economic growth, public debt, and tax revenue. The study leverages population projection methods to compare a baseline projection (with the pandemic's effects) against a counterfactual projection (without the pandemic), isolating the pandemic's contribution to demographic shifts. The first two years of the pandemic witnessed a dramatic rise in mortality, socially patterned with disproportionate effects on historically disadvantaged groups. Simultaneously, fertility rates dropped in 2020, likely due to economic insecurity, followed by a smaller increase in 2021. International migration to the U.S. was severely curtailed, mainly due to the implementation of Title 42, resulting in a significant reduction in net migration. This research addresses the gap in knowledge regarding the combined effects of these disruptions on future population size and age structure, providing valuable insights for policymakers and researchers.

Existing literature demonstrates the independent impacts of the COVID-19 pandemic on mortality, fertility, and migration in the U.S. Studies have shown increased mortality, particularly among older and marginalized populations, alongside decreased birth rates and reduced international migration. However, the literature lacked a comprehensive analysis of the combined and long-term effects of these simultaneous changes on population structure. Two exceptions examined the impact of the pandemic in Spain and Australia using scenario approaches but were country-specific. This study addresses this gap by offering a quantitative analysis focused on the United States, using a comprehensive modeling approach that incorporates the interconnected nature of mortality, fertility, and migration patterns.

The study employs a two-sex cohort component projection model using data from the 2022 United Nations World Population Prospects (UNWPP). The UNWPP data provide baseline projections incorporating the pandemic's effects on mortality, fertility, and migration. A counterfactual projection is created by adjusting the 2020-2024 data to reflect pre-pandemic levels of these demographic factors, assuming a return to pre-pandemic trends thereafter. The difference between the baseline and counterfactual projections quantifies the pandemic's impact on population size and age structure by year, age group, and sex. A stochastic modeling approach, utilizing binomial and Poisson distributions for mortality and fertility projections, respectively, is employed to generate confidence intervals. To isolate the contribution of each demographic process (mortality, fertility, migration), the model is run three times, holding two processes constant while varying the third to counterfactual values. The study calculates total, young-age, and old-age dependency ratios to assess the pandemic's effects on the economic burden of supporting dependent populations. The analysis extends to 2060, with acknowledgment of increasing forecasting uncertainty beyond this timeframe.

The analysis reveals several key findings. First, compared to a counterfactual scenario without the pandemic, the U.S. population in 2025 is projected to be over 2.1 million (0.63%) smaller, with this difference persisting at 1.7 million (0.44%) in 2060. Changes in migration are projected to have the most significant long-term impact on population size. The largest absolute short-term reduction is observed in the 15-49 age group, more pronounced for males than females. Relative reductions are most significant in the 85+ age group. The study observes a cyclical pattern in population differences between the baseline and counterfactual projections, suggesting the pandemic's reverberating effects over time. Secondly, the number of people in the reproductive age group (15-49) is projected to be lower over the next four decades. This is partly attributed to reduced migration in childbearing ages and the second-order effects of lower fertility rates and higher mortality on birth cohorts. Thirdly, the COVID-19 pandemic leads to a small reduction in the dependency ratio, initially driven by increased mortality among older individuals but partly offset by reduced migration. The net effect on the dependency ratio is projected to be slightly smaller in 2025 but may become slightly positive later, driven by changes in migration. Disaggregating the effects by demographic processes reveals the differing impacts of mortality, fertility, and migration on age group composition. Mortality's effect increases the share of younger age groups, while the effect of migration operates in the opposite direction. Despite these combined effects, the overall change in age composition remains relatively small.

The findings demonstrate that the COVID-19 pandemic's effects on U.S. population structure are expected to persist well into the future. While the pandemic's impact on mortality was substantial, especially among older adults, the long-term effects of reduced migration on overall population size are even greater. This highlights the importance of considering the interconnectedness of demographic processes when assessing population dynamics. The projected decline in the reproductive-aged population has significant implications for future economic growth and the ability to support an aging population. The relatively small but persistent changes in the dependency ratio suggest a need for long-term adjustments to social security and healthcare systems. The study's limitations, such as relying on UNWPP's medium scenario projections and the use of model migration schedules, should be considered when interpreting the results. However, the findings underscore the importance of developing comprehensive models to anticipate and mitigate long-term societal impacts of future pandemics or similar crises.

This study provides novel insights into the long-term effects of the COVID-19 pandemic on the U.S. population. The findings highlight the substantial and persistent impact of reduced migration on population size, the decrease in the reproductive-aged population, and the relatively small but significant impact on the dependency ratio. The study emphasizes the importance of considering the interwoven effects of mortality, fertility, and migration in population projections. Future research should explore the longer-term impacts of long COVID, and the continued effects of economic insecurity and shifts in migration patterns on future population trends, alongside investigations into the impact of other similar public health challenges.

The study's findings are based on the UNWPP's medium scenario, which inherently involves uncertainty. The use of model migration schedules to distribute net migration across age and sex groups introduces potential limitations. The study assumes a return to pre-pandemic levels of mortality, fertility, and migration after 2024, which may not accurately reflect the long-term consequences of the pandemic. Indirect consequences of the pandemic, such as long COVID and its effects on mortality and fertility, are not fully accounted for in this analysis.