I saw a comment in an older thread saying that MMR was considerably less effective before 18 months. Does anyone know of sources corroborating or disproving this? (I'd ask the poster who said it, but the thread is really old and they're probably not still watching it.) I'm going to look into it myself as well, but if someone already knows I'm interested in the information.
Measles Vaccine Efficacy during an Outbreak in a Highly Vaccinated Population: Incremental Increase in Protection with Age at Vaccination up to 18 Months
G. de Serres, N. Boulianne, F. Meyer and B. J. Ward
Epidemiology and Infection