What Ioannidis is advocating is to do nothing until we have scientific certainty of what the correct decision should be, and only then act. What he's not taking into account is that the situation is unfolding right now, and if "do nothing" turns out not to have been the correct decision then you can't go back and change that. If we overreact and cause 20% unemployment for the next year, then a harm has been caused, but if we underreact and 20 million people die, then another harm would have been caused. In the face of this alternative, with not enough data to know the probability of outcome #2, but with enough to know that it can happen, then I think it is rational to choose the route that most surely avoids it.