It was about booking the flight... :/
But, they said to accept/reject the invite by Jan 1st, so maybe they will send out a second round of invites if some people decline
I got an email this afternoon, that's all info I am working off of. I don't know if they went out all at once or not, there might still be more to go out
I know yale immunobiology sent out their interview invitations around the middle of last week. Other than that, places do seem to be taking their time.