Effectiveness of 2024/25 KP.2 Vaccine Against Outpatient COVID-19 in Canada

The Canadian Sentinel Practitioner Surveillance Network used the test-negative design to assess KP.2 vaccine effectiveness (VE) against medically attended outpatient COVID-19 between November 2024 and April 2025 among participants ≥ 12 years. Analyses included 5410 controls (19% vaccinated) and 435 COVID-19 cases (10% vaccinated). Nearly three-quarters (72%) of contributing case viruses were genetically characterized, with XEC (35%) and KP.3.1.1 (38%) variants most commonly identified. Vaccination reduced COVID-19 risk by approximately half (54%; 95% CI: 36-68) relative to unvaccinated individuals. VE was greatest during the first 2 months postvaccination, reducing risk by two-thirds and declining to minimal protection by the fifth month postvaccination.