Estimates of vaccine effectiveness of the updated monovalent XBB.1.5 COVID-19 vaccine against symptomatic SARS-CoV-2 infection, hospitalization, and receipt of oxygen therapy in South Korea - October 26 to December 31, 2023

Abstract

Objectives

We evaluated the vaccine effectiveness of monovalent XBB.1.5 vaccine against symptomatic COVID-19 infection, hospitalization, and the need for oxygen therapy in South Korea.

Design

This study employed a test-negative case-control design. COVID-19 test results in symptomatic subjects from six university hospitals across South Korea were collected (October 26–December 31, 2023). The adjusted absolute and relative vaccine effectiveness were assessed.

Results

In total, 5516 subjects were enrolled: 4,824 were unvaccinated with XBB.1.5, and 692 were vaccinated with XBB.1.5 COVID-19 mRNA vaccines. The absolute vaccine effectiveness when comparing the odds between XBB.1.5 vaccination and no vaccination against symptomatic COVID-19 infection, hospitalization, and oxygen therapy was 65.2% (95% CI, 36.1-81.0), 77.3% (95% CI, 51.1-89.5), and 85.3% (95% CI, 57.8-94.9), respectively. The relative vaccine effectiveness when comparing the odds between XBB.1.5 vaccination and no XBB.1.5 vaccination against symptomatic COVID-19 infection, hospitalization, and oxygen therapy was 57.7% (95% CI, 34.7-72.6), 64.3% (95% CI, 35.9-80.2), and 65.5% (95% CI, 27.0-83.7), respectively.

Conclusion

The short-term effectiveness of the XBB.1.5 vaccine against symptomatic COVID-19 infection, hospitalization, and receipt of oxygen therapy in South Korea was significant. Long-term vaccine effectiveness warrants evaluation, and these assessments should be conducted regularly.