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COVID-19

Single COVID-19 mRNA Vaccine Dose Provides Similar Protection Against Infection

Strategic Insights

— 1 min read

A new study on COVID-19 vaccines has found that a single dose of the original mRNA vaccine provides similar protection to two doses for immunocompetent individuals aged 5 years in the current setting of high pre-existing immunity. This supports current recommendations for one dose to be given in advance of the respiratory season, regardless of history of infection or vaccination. The study, conducted by Pfizer, suggests that additional doses may be necessary for certain populations, including young children, older adults, and the immunocompromised.

Key Takeaways:

  • A single dose of the original mRNA COVID-19 vaccine provides similar protection to two doses for immunocompetent individuals aged 5 years.
  • The study found that high population immunity to SARS-CoV-2 from prior infection, vaccination, or both was a key factor in the effectiveness of a single dose of the vaccine.
  • The research suggests that a single dose of the vaccine may be sufficient for individuals with a history of prior infection, regardless of vaccination status.
  • The study supports current recommendations for one dose to be given in advance of the respiratory season, but notes that additional doses may be necessary for certain populations.
  • The research was funded by Pfizer and sought to compare the effectiveness of a single dose of the vaccine in individuals with prior SARS-CoV-2 infection to those who were SARS-CoV-2 naive, unvaccinated with prior infection, and vaccinated with one dose with or without prior infection.

Statistics:

  • 18 studies were eligible for inclusion in the systematic review, none of which reported bivalent or XBB.1.5-adapted vaccine effectiveness.
  • The study was registered with PROSPERO (CRD42023453257) and was conducted using the Synthesis Without Meta-Analysis guidelines.
  • The study found that the majority of eligible studies were published January 2021-October 2023.
  • The Newcastle-Ottawa Scale was used to assess bias in the included studies.

Sources:

  • Effectiveness of a single COVID-19 mRNA vaccine dose in individuals with prior SARS-CoV-2 infection: a systematic review. Communications Medicine, 2025,5(1):1-8.
  • Pfizer.

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