Colds and flues are both viral infections. Cold symptoms consist of sore throat, nasal congestion, runny nose, watery eyes, hacking cough and sometimes fever and can be caused from any of two hundred different viruses. Unlike colds, which usually begin in stages, flu comes on quickly, and gives headaches, chills, muscle aches, fatigue, high fever, cough, sore throat and runny nose. There is no such thing as stomach flu. This is caused from other germs.
All flues are respiratory tract infections.
Flu vaccine is made from dead viruses that stimulate your immune system to make antibodies against those specific organisms. It takes two weeks or more for that to happen, depending on how healthy your immune system is. If you were exposed to the flu or another germ before the two week time is up, you could become sick and mistakenly blame it on the shot. However, the flu shot could make your arm sore or make you achy or even give you a fever for a couple of days. This is because your immune system is being challenged to build up antibodies and may be on temporary overdrive.