Yes, I know about the volcanoes and the lack of summers. But that is not unusual over here- rainy cold summers are the norm- a hot dry one is actually unusual. And the weather here has always been unchangeable- I have set out in the morning many a sunny warm day for it to get cold later on rain and get soaked.They didn't have the waterproof coats back then so poor John probably got soaked a lot- we know he got caught on the coaches a lot. This wouldn't have helped him.
But the point I was trying to make earlier is- that stress can weaken the immune system, so his stresses wouldn't have been helping and may have weakened his immune system.