 Frank Macfarlane Burnet showed in the early 1950s that the virus recombines at high frequencies, and Hirst later deduced that it has a segmented genome.In 1949, John F. Enders (1897–1985) Thomas Weller (1915–2008), and Frederick Robbins (1916–2003) grew polio virus for the first time in cultured human embryo cells, the first virus to be grown without using solid animal tissue or eggs.Infections by poliovirus most often cause the mildest of symptoms.