Original sentence: According to the oral polio vaccine (OPV) AIDS hypothesis, the AIDS pandemic originated from live polio vaccines prepared in chimpanzee tissue cultures (at least some of which were almost certainly contaminated with chimpanzee SIV) which were administered to up to one million Africans between 1957 and 1960.The specific populations, who may not have been properly informed of the risks before volunteering for the vaccination, were the first in the world to experience HIV-1 infections and AIDS some five to twenty years later
Edited sentence: According to the oral polio vaccine (OPV) AIDS hypothesis, the AIDS pandemic originated from live polio vaccines prepared in chimpanzee tissue cultures (at least some of which were almost certainly contaminated with chimpanzee SIV) which were administered to up to one million African "volunteers" in the 1957-1960 period.The specific populations where the vaccine was given were the first in the world to experience HIV-1 infections and AIDS some five to twenty years later