Global Estimates of Lives and Life-Years Saved by COVID-19 Vaccination During 2020-2024

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Conflicts of Interest

Identified Weaknesses

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Paper Summary

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2.5 Million Lives Saved by COVID-19 Vaccines, Mostly Seniors: A Global Estimate

This study estimates that over 2.5 million deaths and 14.8 million life-years were saved globally due to COVID-19 vaccination between December 2020 and October 2024. The majority of the benefits (around 90% of lives saved and 76% of life-years saved) were among people aged 60 or older, and children and young adults had minimal contributions. It is important to note that these results rely on several assumptions about key parameters with inherent uncertainties, and sensitivity analyses suggest a wide range of possible values for the lives and life-years saved.

Possible Conflicts of Interest

None identified

Identified Weaknesses

Reliance on Assumptions and Estimates with Uncertainty

The study relies on multiple assumptions and estimates for key parameters like infection fatality rate (IFR), vaccine effectiveness (VE), and the proportion of the population infected at different stages. These parameters have considerable uncertainty and vary widely across studies and regions, especially for countries with limited data.

Retrospective Observational Design and Potential Biases

The study's retrospective nature and the lack of a randomized controlled trial introduce inherent biases that are difficult to fully adjust for. Factors like vaccine hesitancy and healthcare access may confound the relationship between vaccination and mortality.

Aggregation of Heterogeneous Data Across Countries

The study aggregates data from countries with vastly different pandemic experiences, vaccination strategies, and healthcare systems. This variation could make global estimates less representative and limit the generalizability of the findings.

Counterfactual Assumptions About Omicron Infections and IFR Estimates

The study assumes that unvaccinated individuals would have been infected during the Omicron period, and their IFR estimates are derived mainly from pre-vaccination data. This is likely a counterfactual and could be an oversimplification of the reality during the Omicron period.

Complexity and Uncertainty of Life-Year Calculation

The study's calculations for life-years saved rely on assumptions about life expectancy and the standardized mortality ratio, which can be complex and subject to interpretation, especially in older age groups.

Lack of Separation Between Deaths Averted and Deaths Due to Vaccine Harm

The study calculates "deaths averted" due to vaccine efficacy, without separating deaths from vaccination-related harms. While acknowledging they are likely small compared to the overall benefit, this distinction would provide a more complete picture of the vaccine impact.

Limited Consideration of Non-Fatal Outcomes and Adverse Events

The focus is mainly on mortality benefits, and non-fatal outcomes and adverse effects are not quantitatively assessed.

Rating Explanation

This study addresses an important question with a large scope, attempting to quantify the global impact of COVID-19 vaccination on mortality. While the authors acknowledge the limitations and uncertainties associated with their methodology, the reliance on multiple assumptions, the retrospective observational design, and the aggregation of heterogeneous data across countries introduce potential biases that affect the reliability and generalizability of the findings. Therefore, a rating of 3 is appropriate, recognizing its contributions but also its inherent limitations.

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