Stewien, Klaus E., and José P. G. de Lacerda. 1975. “ Application of the Neutralization Index Comparison Technique to the Intratypic Serodifferentiation of Type 1 and 3 Poliovirus Strains, Using Hep-2 Cell Cultures ”. Revista De Saúde Pública 9 (2): 221-28. https://doi.org/10.1590/S0034-89101975000200012.