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In page Smallpox vaccine:

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Vaccinia was first grown in cell culture in 1931 by Thomas Milton Rivers. The WHO funded work in the 1960s at the Dutch National Institute for Public Health and the Environment (RIVM) on growing the Lister/Elstree strain in rabbit kidney cells and tested it in 45,443 Indonesian children in 1973, with comparable results to the same strain of calf lymph vaccine.[3]: 588–589  Two other cell culture vaccines were developed from the Lister strain in the 2000s: Elstree-BN (Bavarian Nordic) and VV Lister CEP (Chicken Embryo Primary, Sanofi Pasteur).[1][5][6] Lister/Elstree-RIVM was stockpiled in the Netherlands, and Elstree-BN was sold to some European countries for stockpiles.[1] However, Sanofi dropped its own vaccine after it acquired Acambis in 2008[citation needed].