I can tell you that Vanderbilt has been doing a lot of little mini-waves of waitlist pulls recently. Between each one, they request all waitlist people to reconfirm their interest. I think many of these schools are seeing a larger number of deferrals, since a lot of them have modified their rules to be more flexible. Plus, they are not giving as much money as they usually do to students that they are accepting, so many are declining the offer from the waitlist. Interesting times!
As a side note, my son was waitlisted at 4 schools, and has been pulled from 3 of them. Don’t think WashU will end up coming for him, though. 