What should I do about the large discrepancies in vaccine efficacy against the Delta variant being reported across studies?


A: Delta variant, waning immunity, imperfect measurement, or something else? There are a number of reasons why COVID-19 vaccine efficacy may differ across studies. These new reports are measuring the effectiveness of the vaccines in real world settings instead of in a clinical trial. Isolating individual variables in a real-world setting can be difficult. Instead,