vaccine efficacies of 70-90%. That said, one of the trials inadvertently administered a partial dosage which, interestingly, boosted efficacy.
So, what do all these claims mean and how can we evaluate them to make informed decisions in the weeks and months to come?The point of a vaccine is clear: it should result in much less harm than exposure to the virus.
And this is what a vaccine trial attempts to measure—the counterfactual.Since we can never know what would have happened sans the vaccine, we have to estimate the difference between those who have been treated or vaccinated and a control group that has not been vaccinated but is as close to the vaccinated group as possible.