Did the end of smallpox vaccination cause the explosive spread of HIV? — ScienceDaily

Vaccinia immunization, as given to prevent the spread of smallpox, produces a five-fold reduction in HIV replication in the laboratory. Researchers suggest that the end of smallpox vaccination in the mid-20th century may have caused a loss of protection that contributed to the rapid contemporary spread of HIV.
— Read on www.sciencedaily.com/releases/2010/05/100517204405.htm