WHO have created a definition for adequate COVID-19 vaccine effectiveness,3 in which the vaccine effectiveness against symptomatic infections should be at least 70% with a lower 95% CI of at least 50%, and the vaccine effectiveness against hospitalisations or mortality should be at least 90% with a lower 95% CI of at least 70%. In this systematic review, we assessed results in terms of statistically significant reductions in vaccine effectiveness from baseline and meeting these WHO criteria.
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