[Tag] [Tag] [Tag] [Tag] [Tag] [Tag] [Tag] [Tag] [Tag] [Tag] [Tag] [Tag] [Tag] [Tag] [Tag] [Tag] [Tag] [Tag] [Tag] [Tag] [Tag] [Tag] [Tag] [Tag] [Tag] [Tag] [Tag] [Tag] [Tag] [Tag] [Tag] [Tag] [Tag] [Tag] [Tag] [Tag] [Tag] [Tag] [Tag] [Tag] [Tag] [Tag] [Tag] [Tag] [Tag] [Tag] [Tag] [Tag] [Tag] Who is saying 74 million adults would not be immune? You? Does immunity wane? Yes. In most people? No. 
Regardless- say it did - do you prefer outbreaks of millions per year in US? If so, then you think measles is fine? If so- why care about waning immunity in > 50 year olds?