The flu shot is a vaccine given with a needle, usually in the arm. The seasonal flu shots protects against the three or four influenza viruses that research indicates will be most common during the season.
CDC recommends use of any licensed, age-appropriate influenza vaccine during the influenza season, including inactivated influenza vaccine [IIV], recombinant influenza vaccine [RIV], or live attenuated influenza vaccine (LAIV). No preference is expressed for any influenza vaccine over another. Both trivalent (three-component) and quadrivalent (four-component) flu vaccines will be available.