Global COVID-19 vaccination uptake across the emergency and early post-emergency periods, 2021-2024

Problem Statement
The paper addresses the need to understand the trajectory of global COVID-19 vaccination coverage as the world transitioned from the emergency phase of the pandemic to a post-emergency period. While vaccination was critical in altering the course of the pandemic and protecting high-risk groups, the benefits were not experienced equally. Early access to vaccines was uneven, and disparities in supply, policy, delivery capacity, and demand created marked heterogeneity in country uptake. As the Public Health Emergency of International Concern (PHEIC) designation was lifted, the focus shifted from rapid, population-level scale-up of primary vaccination to sustaining protection among high-risk groups (older adults, health and care workers, and those with chronic conditions) through periodic revaccination and integration into routine immunization services. The study seeks to characterize the pace and extent of vaccination during the emergency period (2021–2023) and describe the evolution of uptake patterns in the first full post-emergency calendar year (2024), highlighting persistent gaps and disparities.

Methodology
This study presents a global longitudinal analysis using aggregate, country-reported administrative vaccination data submitted to the World Health Organization (WHO).

• Data Sources: Data were compiled from WHO regional reporting processes, the WHO-UNICEF electronic Joint Reporting Form (eJRF) COVID-19 module, annual routine immunization exercises, and the European Surveillance System (for EU Member States in 2024).
• Analytic Periods: Two periods were defined: the "emergency period" (January 2021–December 2023) and the "first post-emergency calendar year" (January–December 2024).
• Indicators:
  • For 2021–2023, four cumulative indicators were analyzed: total doses administered, individuals with at least one dose, complete primary series (CPS), and at least one booster dose.
  • For 2024, reporting was revised to a single annual indicator: individuals having received a COVID-19 vaccine dose.
• Population Groups: Analysis focused on the total population, older adults (defined as ≥60 years or country-specific definitions), and health and care workers (HCWs).
• Data Processing: An anomaly detection and correction framework was applied to 2021–2023 cumulative data to ensure monotonicity and correct reporting artifacts. For 2024, annual values were reconciled from quarterly or annual reports. HCW data for 2021–2023 were adjusted using WHO methods to account for cases where reported vaccination targets were lower than estimated population denominators.
• Analysis: Population-weighted aggregate coverage and uptake were calculated by WHO region, World Bank income group, and COVAX Facility participation category. Cross-country variation was summarized using medians and interquartile ranges. Daily vaccination rates were reconstructed from cumulative dose records to analyze the pace of rollout.

Key Contributions

• First Harmonized Time Series: This study provides the first globally harmonized time series analysis of COVID-19 vaccination coverage across the emergency period, including specific data for older adults and HCWs.
• Empirical Description of 2024: It offers the first empirical description of reported global vaccination uptake in 2024, the first post-emergency year, capturing the shift toward routine program implementation.
• Disparity Analysis: The paper quantifies persistent disparities in both the pace (daily vaccination rates) and extent (coverage levels) of vaccination across income groups, regions, and COVAX participation categories.
• Policy-Uptake Correlation: It links national vaccination policies in 2024 with reported uptake data, illustrating how policy shifts toward priority groups correlate with heterogeneous uptake levels.

Results

• Emergency Period (2021–2023) Coverage: By the end of 2023, global CPS coverage reached 65% in the total population, 82% among older adults, and 91% among HCWs. However, booster coverage was significantly lower: 33% (total), 60% (older adults), and 69% (HCWs).
• Persistent Disparities: Pronounced income-related gradients were evident. In the total population, CPS coverage ranged from 27% in low-income countries (LICs) to 72% in high-income countries (HICs). Booster coverage showed even steeper gradients (4% in LICs vs. 52% in HICs). Similar disparities existed across WHO regions, with the African Region (AFR) showing the lowest coverage and the Western Pacific Region (WPR) and Region of the Americas (AMR) showing the highest.
• Pace of Rollout: Daily vaccination rates peaked earlier and at higher intensity in HICs and self-financing countries compared to LICs and COVAX AMC-supported countries. Lower-income settings scaled up more slowly and at lower peak delivery rates.
• Post-Emergency Period (2024) Uptake: In 2024, global-level analysis focused on priority groups due to changes in reporting indicators. Among reporting countries, population-weighted annual uptake was 12% for older adults and 6% for HCWs. Uptake varied significantly by income group and region (e.g., 20% for older adults in HICs vs. 5% in LMICs; 15% for HCWs in AMR vs. 0% in SEAR).
• Policy Landscape: In 2024, national policies most commonly recommended primary vaccination and periodic revaccination for priority groups (77% for older adults, 71% for HCWs), while recommendations for broader age groups (adults, children) were less consistent or non-existent.

Significance and Claims
The paper claims that while emergency vaccination efforts achieved broad reach for primary series vaccination, particularly among priority groups, progress was deeply uneven. Disparities in access and delivery capacity emerged early and persisted through 2024. The transition from emergency response to routine control revealed that rapid scale-up of primary series vaccination did not necessarily translate into sustained uptake of subsequent doses.

The authors assert that the lower and more heterogeneous uptake observed in 2024 suggests that sustaining COVID-19 vaccination has become a distinct programmatic challenge, complicated by shifting epidemiology, changing demand, and the difficulty of repeatedly reaching adult risk groups through routine platforms. The findings underscore the need for:

1. Stronger, sustainably financed adult immunization platforms.
2. Associated monitoring systems to enhance life-course vaccination benefits.
3. Mechanisms to improve equitable access to vaccines and operational capacity to identify and reach priority groups.

These capacities are deemed essential not only for ongoing COVID-19 control but also for supporting future outbreak, epidemic, and pandemic responses. The study concludes that vaccine equity must be assessed not only by the coverage eventually achieved but also by the speed at which protection reaches populations.