Efficacy In Plain Terms
95% efficacy does not mean that 95% of vaccinated individuals will not get COVID-19 and that the other 5% will get COVID-19. It means vaccinated individuals will be 95% less likely to get COVID-19.
For example, if 1% of the unvaccinated population develops COVID-19 (similar to the Pfizer control group), getting the vaccine would reduce chances of getting COVID-19 by 95%, resulting in a 0.05% infection rate.
For information about in-vitro efficacy against variants, please see question about variants.
Updated: March 1, 2021