Objective:

To report interim estimates of the effectiveness of the 2025-2026 COVID-19 vaccine targeting JN.1 and JN.1-derived sublineages in immunocompetent adults and discuss the test-negative design (TND) for vaccine surveillance.

Approach:

Key Findings:

• The updated COVID-19 vaccine targeting JN.1 and JN.1-derived sublineages reduced ED/UC encounters by 50% (95% CI, 42%-57%) and hospitalizations by 55% (95% CI, 41%-66%).
• The TND design allows for effective vaccine effectiveness estimation without needing a fully enumerated cohort.

Interpretation:

The TND is an approach to estimate vaccine effectiveness in the US, especially given the fragmented nature of health data.

Limitations:

• Confounding by health-care seeking behavior may bias results.
• Frailty bias may occur if individuals at higher risk for severe outcomes are more likely to receive vaccination.

Conclusion:

The TND is a method for routine vaccine effectiveness monitoring, particularly as the infrastructure for electronic health records is strengthened.

Sources:

• Wiegand et al. Study
• CDC Morbidity and Mortality Weekly Report
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