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April 16, 2026BMC Infectious DiseasesOpen Access

Vaccine effectiveness across the Omicron evolutionary spectrum (BA.2, BA.5, XBB, JN.1, KP.3): a systematic review of studies published 2022–2025

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Authors

SASaad AlhumaidOAOla AlkharsAAAbeer S. Algrafi

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Overview

This systematic review assesses COVID-19 vaccine effectiveness against severe outcomes in older adults across Omicron variants, indicating the need for booster vaccinations.

Key Points

  • The study aims to synthesize real-world evidence on COVID-19 vaccine effectiveness against SARS-CoV-2 infection and severe outcomes across Omicron subvariants from 2022 to 2025.
  • Conducted a systematic review following PRISMA 2020 guidelines.
  • Systematically searched databases including MEDLINE, Embase, and CINAHL for relevant observational studies.
  • Included studies assessed vaccine effectiveness across Omicron subvariants after 2022.
  • General vaccine effectiveness against SARS-CoV-2 infection was modest and waned quickly.
  • Updated and variant-adapted vaccines provided significant protection against severe COVID-19 outcomes.
  • Protection against severe outcomes remained above 50% within the first few months of vaccination.

Cite This Study

Alhumaid et al. (2026) studied this question.

synapsesocial.com/papers/69e07c1e2f7e8953b7cbd882https://doi.org/10.1186/s12879-026-13281-y
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Also Consider

Synapse has enriched 5 closely related papers on similar clinical questions. Consider them for comparative context:

  1. 1Implications for future pandemics from a living systematic review and critical evaluation of observational studies of the effectiveness of COVID-19 vaccination against the Omicron variant2026
  2. 2Immune evasiveness of SARS-CoV-2 variants and vaccine selection2024 · 2 citations
  3. 3Effectiveness of XBB.1.5 Vaccines Against Omicron Subvariants2024 · 2 citations
  4. 4Humoral immunity to current variants of SARS-CoV-2 in exposed adults, September 2023 to September 2024.2025 · 2 citations
  5. 5Immunogenicity, clinical efficacy and safety of additional second COVID‐19 booster vaccines against Omicron and its subvariants: A systematic review2024 · 16 citations