2024/25 KP.2 vaccination shows waning protection against COVID-19 hospitalization in adults over 60 in Quebec.

This test-negative study assessed the effectiveness of the 2024/25 KP.2 vaccination against COVID-19 hospitalization in adults over 60 years old eligible for publicly-funded vaccination in Quebec, Canada. The analysis included 49,949 participants followed for up to ten months, comparing vaccinated individuals to non-vaccinated participants in an acute-care hospital setting.

Overall vaccine effectiveness (VE) against hospitalization was 34%. Protection was higher in the initial period, reaching 43% within eight weeks post-vaccination. However, effectiveness declined over time, becoming negligible by the 32nd week post-vaccination. Absolute numbers for outcomes were not reported, and statistical significance metrics such as p-values or confidence intervals were not provided in the available data.

Safety data, including adverse events, serious adverse events, discontinuations, and tolerability, were not reported in this study. The study did not specify funding sources or potential conflicts of interest. Key limitations include the lack of reported absolute numbers and statistical measures, which restricts the precision of the estimates. Additionally, the absence of reported safety data limits the assessment of the vaccine's risk profile in this specific population.

The practice relevance lies in recognizing that the short-lived nature of protection against hospitalization may influence vaccination timing or booster strategies for older adults. Clinicians should interpret these results with caution due to the observational nature of the study and the incomplete reporting of safety and statistical details.