Greenberg RN, Kennedy JS, Clanton DJ, Plummer EA, Hague L, Cruz J, Ennis FA, Blackwelder WC, Hopkins RJ. Safety and immunogenicity of new cell-cultured smallpox vaccine compared with calf-lymph derived vaccine: a blind, single-centre, randomised controlled trial. Lancet. 2005 Jan 29-Feb 4; 365(9457):398-409.