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
David Bruce (microbiologist) discouraged the experiments being carried by Zammit, and doubted his ability as a microbiologist. Eventually, when he learned of the positive results linking the fever with unpasteurized goat milk, Bruce tried to discredit the role of Zammit and take credit to himself. To a certain extent he succeeded, as it was renamed after him as brucellosis, however information about the role of Zammit has eventually surfaced. When he was transferred to South Africa, Bruce was sent to Zululand in 1894 to investigate the outbreak of cattle disease which the native called "nagana". In 1903, he identified the causative protozoan, and