Confused dad: my son's vaccine schedule calls for measles (0) vaccine at 6 months, then mmr (1) at 12 months and mmr (2) again at 6 years. is measles (0) vaccine necessary at 6 months? a few studies suggest lower protection with early immunization.

That's why 3 shots: There's always measles in the world. Bad disease. Can ruin a perfectly normal baby. More kids are susceptible in recent years due to followers of the anti-vaccine crowd. More kids susceptible due to missing vaccines due to COVID lockdowns, but less chance of catching measles (because we are socially distancing). People follow a local shot schedule as it reflects local measles issues and outbreaks.

Basics: An early measles vaccine provides transient protection to children who live in areas where measles in going around. It is a bad disease. That protection to measles would fade some if not boosted at 1 yr & 4-6 yr as you have noted with the MMR given at those times. In regions of the world where measles is rare, the early shot is skipped.