Why give flu shots rather than "booster" injections? Why is last year's flu shot ineffective against this year's flu?

Why give flu shots rather than "booster" injections? Why is last year's flu shot ineffective against this year's flu?

which of the following methods would be the best type of vaccination for fending off the flu, and explain your reasoning:

A. IM (intramuscular) Injection

B. Nasal Spray

C. ID (intradermal) injection