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Coronaviruses

Fourth Dose of Ancestral-Strain mRNA Vaccines Provides Modest Additional Protection Against COVID-19 Infection

Strategic Insights

— 1 min read

A recent study conducted in Qatar has shed light on the effectiveness and durability of a fourth dose of ancestral-strain mRNA vaccines against SARS-CoV-2 infection. The research, published in the journal Scientific Reports, found that the fourth dose conferred modest additional protection against infection, with an adjusted hazard ratio for infection of 0.91 (95% CI: 0.81-1.02), corresponding to a relative vaccine effectiveness of 9.2% (95% CI: - 1.7 to 18.9%). The study's findings highlight the need for next-generation vaccines offering more durable immunity.

Key Takeaways:

  • The fourth dose of ancestral-strain mRNA vaccines provided a modest additional protection against SARS-CoV-2 infection, with a relative vaccine effectiveness of 9.2%.
  • The protection peak within the first three months of vaccination at 35.0% (95% CI: 20.6-46.8%) but waned rapidly thereafter, becoming negligible beyond that period.
  • The study supported the need for next-generation vaccines offering more durable immunity against COVID-19.
  • The research was a nationwide matched cohort study conducted in Qatar between February 10, 2021, and May 13, 2024.
  • The study used a matched cohort design to evaluate the relative effectiveness and durability of the fourth dose of ancestral-strain mRNA vaccines.
  • The research was conducted by a team of researchers from Weill Cornell Medicine - Qatar, in collaboration with other institutions.

Statistics:

  • The adjusted hazard ratio for infection after the fourth dose was 0.91 (95% CI: 0.81-1.02).
  • The relative vaccine effectiveness of the fourth dose was 9.2% (95% CI: - 1.7 to 18.9%).
  • The protection peak after the first three months of vaccination was 35.0% (95% CI: 20.6-46.8%).
  • The study was conducted between February 10, 2021, and May 13, 2024, in Qatar.

Sources:

  • Effectiveness and durability of a fourth dose of ancestral-strain mRNA vaccines against SARS-CoV-2 infection: a nationwide matched cohort study in Qatar (2025;15(1):35179).
  • Scientific Reports (www.nature.com/srep/).
  • NewsRx. Findings from Weill Cornell Medicine - Qatar Broadens Understanding of COVID-19 (Effectiveness and durability of a fourth dose of ancestral-strain mRNA vaccines against SARS-CoV-2 infection: a nationwide matched cohort study in Qatar). Medical Letter on the CDC & FDA. October 26, 2025; p 59.

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