Risk-Based Prioritization for COVID-19 Vaccination in the Post-Emergency Phase
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Importance
As COVID-19 transitions from an acute emergency to an endemic threat, yearly universal boosting policies may not be necessary. Quantifying absolute benefits of differing age– or risk-based vaccination strategies is critical for efficient allocation.
Objective
To estimate the absolute benefit of COVID-19 vaccination strategies in the post-emergency phase based on the number needed to vaccinate (NNV) to prevent moderate-to-severe COVID-19 hospitalization, defined per Israeli Ministry of Health criteria (pneumonia with hypoxia or need for respiratory support), across risk strata.
Design, Setting, and Participants
This retrospective, population-based cohort study included all individuals aged 12 years or older enrolled in Clalit Health Services, Israel’s largest healthcare organization, between March 1, 2020, and March 1, 2025. Data from the emergency phase (March 1, 2020 to July 31, 2022) were used to empirically estimate the risk of COVID-19 hospitalization across three dimensions: age group, comorbidity category, where each participant was classified into one of 16 groups according to the condition associated with the highest observed risk, and history of all-cause hospitalizations within the past 1 to 3 years. This risk-based classification, derived from the emergency phase, was then applied to the post-emergency phase to identify high-risk groups.
Main Outcomes and Measures
NNV to prevent moderate-to-severe COVID-19 hospitalization.
Results
The study included 3.6 million individuals with 39,571 COVID-19–related hospitalizations in the emergency phase and 10,141, in the post-emergency—an effective 4.3 annual decline. During the emergency phase, hospitalization risk ranged from 68 per 100,000 among healthy adults aged 12–49 years to 9,999 per 100,000 among those aged 75 years or older with severe chronic illness and recent hospitalization. In the post-emergency phase, risks declined to 5–3,230 per 100,000 within the same groups. NNV ranged from fewer than 100 in high-risk older adults to over 40,000 in younger healthy adults. Using NNV thresholds of 1,000–2,000, 7.2%–10.0% of the population would be prioritized for vaccination, representing 79%–88% of all COVID-19–related hospitalizations.
Conclusions and Relevance
COVID-19 continues to pose considerable risk to vulnerable populations. Consideration of risk factors beyond age can inform more efficient vaccine allocation strategies for ongoing booster doses, particularly by accounting for all-cause hospitalizations in the past 1–3 years.
