The interim readouts from the studies follow a predetermined pattern. Volunteers in the vaccine studies are randomized to either receive a vaccine candidate or placebo. Both volunteers and those administrating the vaccines shots are blinded to study, meaning they do not know if a vaccine or placebo has been given. Each individual remains blinded until either a severe adverse side effect occurs (which we have not publicly seen so far in either Pfizer’s or Moderna’s trials) or if a person in the study test positive for COVID-19. In the case of Moderna’s trial, once 95 study participants have tested positive an interim readout in conducted to see if there is a trend towards vaccine effectiveness. So far, that trend looks overwhelmingly in favor of the vaccine stopping COVID-19 spread. Of the 95 volunteers with confirmed positive COVID-19 tests, 90 received placebo and only 5 got the vaccine, resulting in the 94.5% efficacy measure.

Shortly, drug regulators will look into granting both Pfizer and Moderna emergency use approvals. By then we will have seen additional interim readouts from the studies and importantly, a at least a few months of safety follow-up.

Technologically, the Moderna and Pfizer vaccines belong to a new type of immunization that has not been used commercially before but has enabled unprecedentedly fast vaccine development. These vaccines contain messenger RNA, or mRNA, which essentially tells human cells to manufacture a non-infectious part of the SARS-CoV-2 virus. More precisely the protein that the virus uses to attach to host cells. The protein is identified as foreign by the immune system so that when the real virus enters the body, the immune system is already primed to recognize it and start attacking the virus.