> Yes, with the control group you would have a base for how many people you would have expected to be infected, so there's that, but you "could" get that from o

> Yes, with the control group you would have a base for how many people you would have expected to be infected, so there's that, but you "could" get that from other observations. Getting this number for a distribution of people as similar as possible to the people in the experimental group is, in fact, the primary purpose of having a control group. There is no better way to predict this number, as you can't predict how likely a particular person is to catch coronavirus at a particular time, in a particular location. You also need a control group to get the number of various medical problems expected in the experimental group, even if the vaccine doesn't cause them. This also depends on time, place, and behavior. So, if you create a reason for people in the control group to behave differently from experimental group, for instance by letting people find out which group they are in, you defeat the purpose of having a control group.