Question

How should we read '95% efficacy' — what is it a percentage of?

DOdortiz· 3 days ago

A frequent public misunderstanding: 95% efficacy is the relative reduction in symptomatic cases vs placebo, not '95% of vaccinated people are protected' or '5% get sick'. What's the clearest way to explain relative risk reduction vs absolute risk to a general audience without losing the trial's actual meaning?

Public Health

1 Reply

Accepted answer

WEweizh3 days ago

I usually frame it as: among comparable people, the vaccinated group had ~1/20th the symptomatic cases of the placebo group over the study window. The absolute risk depends on background incidence, which is why both numbers matter when communicating.