What does "pre-vaccinated" mean in this context, exactly? Vaccinations only come in the "pre" variety; once you've caught the disease, vaccination is unlikely t

What does "pre-vaccinated" mean in this context, exactly? Vaccinations only come in the "pre" variety; once you've caught the disease, vaccination is unlikely to do any good. Some diseases (e.g.: rabies) have a long enough incubation period that post-exposure prophylaxis is effective, but this is very much the exception. Sure, kids can get measles, and they'll probably be just fine. Measles only has a 0.1%-0.2% mortality rate, after all... On the other hand, that means 1-2 of every 1,000 children who get the disease will die a completely pointless and preventable death.