How can he have been vaccinated at 10mo? The MMR is given at 12mo, not 10mo?
Surely he is unvaccinated as yet. Which is why here immunity is essential, to protect those who are unable to get vaccinated due to being too young, and those that can't be vaccinated for medical reasons.
Despite being severely concerned about the Autism links (now disproved), I still vaccinated my DC's, albeit 6 months Kate for first dose, and 9 months late for second dose, on the advice of my paed consultant at the time, so they were all still vaccinated.
DS3, 19mo today, hasn't had his MMR yet, on the advice of the dietician I was asked to hold off as he has severe, life threatening allergies, and we hadn't yet introduced egg to his diet, and the MMR vaccine is prepared in egg.
Now that we know he is not allergic to egg, his appointment for vaccination is next week.
OP, I am sorry that your young baby has measles.