According to the product text, the intramuscular route of administration is recommended, vaccinating adults and older children in the deltoid muscle, using a needle 1 inch in length or greater, in order to penetrate the muscle tissue.
Medical Photos – Influenza Vaccinations
Medical workers giving flu vaccinations to children, men and women.
Asian Man Receiving an Immunization
Depicted in this 2006 image, this man was receiving an intramuscular immunization in his left shoulder muscle. He was facilitating the procedure by lifting up his sleeve, while the nurse admistered the vaccine. With her free hand, the nurse stabilized the injection site.