We both had flu a couple of years ago. I was sick in bed for 3 months, he was up and around and taking care of me.
In my case I haven’t had a cold in 47 years and only one case of the flu in the last 37 years which was a mild three day annoyance. I don’t think it’s possible that I’ve gone all those years without ever contacting those viruses in some way.
Viruses affect different people in different ways.