Yes, I thought so too. Maybe Healers would begin with routine and then switch to the more obscure treatments when that didn't work. And immunisation sounds good with Herbology! I can see than happening. Maybe shoot something into the blood with the wand or something. Non-painful, kids would giggle when they got shots. :p Thank you, thank you very much! :)
Either way, wizards might act above Muggle practices but I feel like a Healer - or at least a Healer dealing with something as heavy as ALL - would at least attempt to get the parents of the patient to think about the treatment. The treatments themselves would probably be potions until they aren't working well with the patient, then wand-work and the usual spells, and maybe the last resort would be either Muggle doctor techniques or even more experimental techniques. That's generally how treatments are dealt with right? First the tried and true and then slowly try and introduce the 'new' techniques to the patient?
You could lean into the more naturalistic side of magic and maybe introduce a Healer who has studied stuff like ritualistic healing or... well, I dunno. Maybe I'm throwing out too much speculative stuff, but that's all I've got :D
Oh and immunization is tricky. The introduction of the disease/germ could be done a ton of ways - maybe isolation with the germ and careful attention. It's a bit hard without vaccinations but I think you could work out something with that or even Herbology.