Thousands (30) of people are in the trial, half were assigned randomly to the control group. So far 95 people in the trial have caught COVID and, when they unblinded the data, they discovered that 90 of those infections where in the control group. Since participants were randomly assigned into the test group vs the control group and so both groups should have the same amount of exposure, this is a strong signal that the vaccine was effective. Here's an article about Moderna's trial with a link to their 135 page (!) design doc https://www.livescience.com/moderna-vaccine-trial-protocol.h...