The test-negative design: Opportunities, limitations and biases

Area of Science:

• Epidemiology
• Vaccinology
• Biostatistics

Background:

• Test-negative designs are frequently used to estimate vaccine effectiveness.
• Interpretations of test-negative design outcomes require careful consideration of underlying assumptions and limitations.

Purpose of the Study:

• To systematically review the properties and applications of the test-negative design.
• To clarify the interpretation of test-negative design study outcomes.
• To identify the limitations and potential new opportunities for this study design.

Main Methods:

• Systematic literature review of test-negative design properties.
• Analysis of assumptions and limitations in various application contexts.
• Evaluation of suitability for different health outcomes (mortality, hospitalization, transmission).

Main Results:

• The application of test-negative designs does not strictly depend on certain assumptions, potentially broadening their use.
• The design is unsuitable for studying vaccine effects on mortality.
• The design is problematic for assessing vaccine effects on hospitalization and virus transmission, with the latter being highly dependent on test characteristics.

Conclusions:

• Test-negative designs have significant limitations and are often applied in idealized situations.
• The findings suggest that test-negative designs should be interpreted with caution, especially for real-world effectiveness.
• Further research is needed to refine the application and interpretation of test-negative designs in public health.