I've not been audaxing much for a while, but I had entered the Dirty Reiver 200. Looks like they're going to try their best to keep the event going, but I very much think the decision will be taken out of their hands - by 18th April, I'm pretty sure we'll be well into the "Everyone stay in your homes" stage.
As for looking after your immune system - it all starts with sleep, so riding a long event that robs you of that is just daft, at a time when you need it most.