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. Incubation period is for 1-4 days, average 2 days. Persons can be infectious from 1 day before symptoms begin through 5 days after onset.
Kids can be infectious longer.
Flu is spread trough airborne droplets. Get plenty of rest. Stress of all kinds brings on illness be it physical, emotional, spiritual. Vitamin C at least 1000mg day in divided doses. Zinc 30 mg a day.