The MMR vaccine is more effective after 12 months, i.e. there are fewer cases of the vaccine failing to confer immunity when first administered at 12 mos as opposed to earlier.

You can receive a first MMR dose earlier than 12 mos for certain grounds (e.g. international travel, military postings) but it is then recommended that the infant receive a second 'first dose' after 12 months.

IANAMD, but after looking at the vaccination plan for children last week, my guess would be that there's so many vaccines to be taken in the first two years of life that they have to sort it by priority and space out to balance risk of catching a disease with risk of overloading the body.

The evidence seems to indicate that vaccines don't cause some kind of "immune system overload". There are efforts underway to increase the number of vaccines given at a time.

https://www.who.int/vaccine_safety/initiative/detection/immu...

That's good to know. Doesn't stop midwifes from scaring us into considering combined vaccines that reduce the number of injections, solely by arguing that the more injections, the less safe it is for the baby.

Immume systems are fucking amazing[1]. There are millions of viruses and bacteria of all sorts everywhere in your house and outside that a child's immune system is constantly dealing to without you even being cognizant of it. And if it wasn't dealing with those successfully you'd very quickly know about it because your child has an immune disorder. The vaccines are absolutely infinitesimally small in terms of an immune reaction compared to this every day constant barrage.

[1] Except when they're broken, and then it sucks bad, and you find out how damn amazing they are and how much we take them for granted.