people underestimate immune systems lol.
you can get instantly sick in 1 night just be being out in the rain. all it takes is 1 forgeted up thing to make your body cold or something, and the viruses that are all over us at any moment already, will just infect.
but a few Vit-c pills, or some fruit or juice that day could prevent it from happening. its literally that easy and fast working.
or you could just get drugs and cross your fingers for the year.