Vaccinations

[KSdancer]

I have had 2 major diseases wipe out a lot of my flock. Two years ago we had mericks and then just a couple of months ago we had ILT I believe was the name. I have had vets tell me different things and wanted more opinions. We stopped buying chickens from stores or ordering them and just hatching our own so we don't bring in outside birds. One vet told us we should pretty much get rid of all of our hens and only buy ones with all their vaccinations then others say it doesn't matter as long as we either have birds with all vaccinations or birds with none. So I am really confused and just want to make sure I keep my flock healthy and not have these big population drops. Please give me your opinions!