Just on the immunity amongst those that have had it. Me and 4 other's from work were struck down with this in March, utterly fucked us and I was off for weeks.
Currently this thing is ripping through my team. Of 35 people 20 are now off, 16 went in one go and are suffering the typical no taste, no energy just laid up with it. Meanwhile the 5 of us fine, it's hardly scientific but personal experience.