Polio vaccine is usually provided in vials containing 10–20 doses of vaccine. A single dose of oral polio vaccine (usually two drops) contains 1,000,000 infectious units of Sabin 1 (effective against PV1), 100,000 infectious units of the Sabin 2 strain, and 600,000 infectious units of Sabin 3. The vaccine contains small traces of antibiotics—neomycin and streptomycin—but does not contain preservatives. In a generic sense, vaccination works by priming the immune system with an 'immunogen'. Stimulating immune response, by use of an infectious agent, is known as immunization. The development of immunity to polio efficiently blocks person-to-person transmission of wild poliovirus, thereby protecting
His Name Is Legs (Ladies and Gentlemen) for "His Name Is Legs" included tack piano, played by Canadian musician David Foster, and a new horn arrangement, played by Scott and Chuck Findley, another member of Harrison's tour band the previous year. Scott and Findley recorded their contributions at A&M Studios over 2–3 June, with each musician overdubbing two horn parts.<ref name="Extra Texture/YouTube">George Harrison interview, "Rockweek", (retrieved 13 September 2013).</ref> The released recording begins with an introductory bass riff from Weeks, which is then joined by Foster's tack piano. Commentators note the lack of clarity in the mix, which author Elliot Huntley attributes to the "three-pronged piano attack"