At current state-level vaccination rates, measles may become endemic again; increasing vaccine coverage would prevent this. Under a 50% decline in childhood vaccination in the US, the simulation model predicted 51.2 million measles cases over a 25-year period, 9.9 million rubella cases, 4.3 million poliomyelitis cases, 197 diphtheria cases, 10.3 million hospitalizations, and 159 200 deaths.