Have a 4 month old and worried about measles

[HHH3]

I've just been told we have measles nearby and I'm really worried...

DS2 is 4 months old so obviously hasn't been vaccinated yet (DS1 is 8yo and has had both jabs). I had the single measles vaccine (pre MMR) but have no idea if I'm still immune or if I'm passing any immunity on to him.

Is there anything I can do? Can't avoid people as, if nothing else, he has to come with me on the school run. Trying not to panic but I'm really worried