sentence: Attenuated virus is a much less harmful strain of the same virus.
sentences_before: The first was developed by Jonas Salk and first tested in 1952. An oral vaccine was developed by Albert Sabin using attenuated poliovirus.
sentences_after: Human trials of Sabin's vaccine began in 1957 and it was licensed in 1962.
concept_name: attenuated virus
headings: Polio vaccine
categories: Immunization