The XBB.1.5 COVID-19 vaccine elicits a durable antibody response to ancestral and XBB.1.5 SARS-CoV-2 spike proteins

Sep 3, 2025Science translational medicine

The XBB.1.5 COVID-19 vaccine produces lasting antibodies against original and XBB.1.5 coronavirus spike proteins

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Abstract

The XBB.1.5 COVID-19 vaccine induced durable antibody responses with half-lives of 703 days for WA1 and 531 days for XBB.1.5 IgG spike protein binding antibodies.

  • A single dose of the XBB.1.5 mRNA vaccine increased the magnitude and breadth of neutralizing antibodies against ancestral and variant SARS-CoV-2 strains.
  • IgG1 and IgG4 binding antibodies against the XBB.1.5 spike protein were significantly higher than those against the WA1 spike protein after vaccination.
  • High cross-reactivity of antibodies against both WA1 and XBB.1.5 strains was observed and remained durable over time.
  • Six months post-vaccination, neutralizing antibodies showed reduced effectiveness against circulating Omicron variants KP.2 and KP.3 compared to XBB.1.5.
  • Findings suggest that while the XBB.1.5 vaccine promotes stronger and longer-lasting antibody responses, emerging variants may still evade these defenses.

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