The College Student's Immune System

Sometime within the first 3 weeks of the semester: 
"AHH! So many people! So many germs!! Cannot fight them all!" 
You get a small cold

First half of semester until flu vaccine:
"Healthy, healthy, healthy..."

After flu vaccine:
"This kid hasn't eaten nutritious food in 2 months, they're sleep-deprived, and stressed...and they just got a vaccine. OVERLOAD!"

After finals week: 
Somehow, your immune system knows you need to make it through finals. You deprive yourself of sleep, eat snack foods because you can't stop studying to get a meal (not to mention you eat at incredibly irregular hours), and possibly don't shower as often as you should. But it's not until the morning after you get home that your immune system finally says, "Well, now that you're done being stressed, we need to clean house. Time to be SICK!"