outch - what bad luck. Since the MMR was given some days before the first pox, there is a good chance of immunity anyway... Chicken pox incubation time is two to three weeks, so he'd have caught them a week or longer before the MMR. I hope he'll sail through this without too much bother! Usually, new pox appear for about 5 days and he is no longer contagious once all of them have crusted over. Good luck!
Dh was wondering if cp can lie dormant and perhaps the vaccinations just put them under the weather enough for it to come out.
Dd had her preshool boosters then came down with cp about 2 weeks afterwards then ds has had the same but less than a week. The strange thing is with both of them we have no idea where they got it having not been in contact with any cp.
Not strange really tbh. Chickenpox is at its most infectious before the spots come out so you're more likely to catch it from someone who looks like they don't have it (if that makes any sense).
The virus is spread mainly through droplet contact I think and can survive outside the body for a short time - this is off the top of my head, but I think you're talking 15 minutes or so. Once you've had it then it'll lie dormant in your system for the rest of your life, unless you're unlucky enough to get shingles later on, but I don't think the virus could be dormant in the body without a reaction first (albeit a mild one - some people are immune to chickenpox and don't ever recall actually getting it).
I guess with chickenpox being so commonplace in children and vaccinations also being routine what seems like a big coincidence - two children coming down with chickenpox shortly after vaccination - probably isn't really if you look at the whole population.