Influenza vaccine protects against certain strains of influenza. Since the strains of influenza that circulate change every year, it is necessary to make a new influenza vaccine for each winter . This is why a yearly flu shot is recommended. Influenza vaccination cannot cause influenza because the vaccine does not contain live virus. Minor soreness at the injection site lasting up to two days is common.
Allergic reactions are rare.
Flu vaccine contains a minute amount of egg protein, which may cause an adverse reaction in some people. If in doubt, check with your doctor. For most people, the flu usually lasts six to eight days. Symptoms include fever, headache, coughing, loss of appetite, muscle aches, fatigue, and sometimes stomach ache and diarrhea. Children and teenagers with the flu should take only acetaminophen unless their doctor prescribes otherwise.