Johnson is a public figure and has perhaps been exposed to larger quantities of the virus, which can be a factor in severity of symptoms.
yes viral load is a big factor
this is why doctors who even with PPE can still get sick
they are up close and personal with the very sick(heavy viral load)
[[speculation]: matt hancock is medical minister and visits hospitals, he got sick first, so i suspect he was the path to boris]
we cannot see the virus, but if you imagine it like wet paint.
think about what you come into contact with and what you touch next. the more imaginary paint you get on your hand and then food and then in mouth, the more your body has to react to/handle/deal with
licking a door knob of a bathroom on the corona ward will be millions of times worse than sitting at home on your own and maybe coming into contact with a random letter in the post.
viral load is a big factor.
then is how your bodys immuno response system reacts to things.
what you dont want to do is get to the point where you are struggling to breath and using all your energy on your breathing untill your body cant do it anymore due to low bloodox/worn out.
so for now. just stay away from people limit what you touch. think about what you do before putting anything near your face/mouth.
this includes dont use a facemask if your then going to be constantly touchin it/adjusting it. as your defeating its purpose. and dont wear a mask if your then thinking your immortal to not care what you do with your hand face. again it doesnt work like that.
but to make things very simple
imagine everything is wet paint. and minimise how much can get to hand face mouth as possible
(its a easy game that works for kids so should work for idiot adults)