How is vaccine evidence judged?
The same core principles used to assess other health evidence apply: match the design to the question, examine risk of bias and uncertainty, and interpret each result within the wider evidence base.
Six questions to ask
Why one hierarchy is not enough
Systematic reviews and well-conducted meta-analyses often carry substantial weight, but their quality depends on the studies and methods used. Randomised trials can estimate intended effects under controlled conditions; large observational studies and surveillance can answer questions that trials are not designed or large enough to resolve.
How uncertainty should be reported
Uncertainty should be part of the conclusion rather than hidden. A result can support a conclusion without proving it with absolute certainty. Equally, absence of a statistically significant result does not automatically prove that no effect exists.
Sources and further reading
Medical Evidence Review Policy
Educational scope
This guide explains general appraisal principles. It does not provide an individual vaccination recommendation or replace advice from a suitably qualified healthcare professional.