There is overwhelming evidence that one of the best ways to get children to remember something is setting it to music. There is also overwhelming evidence that vaccines are safe and effective at preventing serious diseases, which means parents who ignore that overwhelming evidence are acting like children (or rather, idiots, since children have an excuse for their ignorance).
(Complete disclosure: I had Rubella as an infant, before the vaccination was common and when I was too young to get vaccinated anyway. At the time, Tetracycline was the antibiotic of choice, which saved babies' lives but caused major dental damage, and which has cost me tens of thousands of dollars in dental work and enormous pain. So don't preach to me about how these childhood diseases are benign!!)
Since evidence, rational argument, and logic have failed to convince the anti-vaccine crowd, maybe we need to set it to music . . . .