Vaccines prevent diseases and that's awesome because even relatively mild diseases like measles and chickenpox kill or disable a minor share of the people they infect. So it is without a doubt that vaccines have prevented billions of sick days and saved many many lives (don't even go there, anti-vaxxers).
But there's another important benefit of vaccines that I've never seen highlighted - the time they save the parents by reducing the amount of time they have to spend taking care of sick children (I had this epiphany last week when both of my children were sequentially sick and home from daycare). And if your child is constantly home sick, even with routine childhood diseases, it makes it difficult to hold down a job. Undoubtedly, in the pre-vaccines era, this burden would have fallen largely on women. Of course, children still get sick, but my guess is that vaccines made it significantly easier for women with children to hold steady jobs. So the research question is, "What is the effect of vaccines on female labor supply?" Potential title of paper: "Vaccines and Female Labor Supply". You're welcome.