I odered a bubch from welp, only have 5 left out of 33, they were vac for mereks, the ones i hatched my self are not vac and they are doing fine. I found out that the mereks vac lowers there immune sytem way down than normal for almost 2 to 3 weeks old, so if they get the slightest chill they wont make it compared to a chick was not vac. so i will never have my chicks vac for the mereks any more.