21 February

Vaccine efficacy is badly explained to the public I think. For example, if a vaccine has a 95% efficacy, I think many (including me) assumed that meant about 5% of people would still get symptomatic Covid disease. Doesn't mean that at all. In a trial they may test 100,000 people, 1% (1000) of which might develop Covid. The 95% efficacy for that 1000 - it means about 50 people would still get symptomatic Covid, 5% of 1000. So 99.95% of that 100,000 total sample would not get symptomatic disease.