The results for both vaccines come from interim analyses of...

The results for both vaccines come from interim analyses of large clinical studies. In the Moderna study there were 30,000 volunteers. Half got two doses of the vaccine 28 days apart, half got two shots of a placebo on the same schedule.

There were 95 instances of COVID-19 illness among the study participants — only five of those cases were in the vaccinated group. Ninety were in the group receiving the placebo. Of these, there were 11 cases of severe disease. The results indicate the vaccine was inducing the kind of immune response that protects people if they were exposed to the coronavirus.