Quadruple vaccine containing 75 D antigen units of killed type 1 poliovirus was given to children at ages 2, 3 and 4 months followed by a booster dose at 15 months.The serological response to the primary course was difficult to assess owing to maternal antibody. Antibody titres to the type 1 component after the booster dose were very satisfactory and about 10 times higher than those observed in a similar group of children given attenuated vaccine. Response to the poliovirus types 2 and 3 in the quadruple vaccine was less satisfactory.Graded doses of attenuated poliovirus type 1 were fed to the children 2 months after the primary course and 1 month after the booster dose. Children who had received no poliovaccine and children immunized with attenuated vaccine were included for comparison.Immunization with killed vaccine did not greatly affect the size of the minimal infecting dose of live virus but reduced both the duration of the subsequent infection and the titre of virus in the faeces.The epidemiological significance of these findings is discussed.

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A simple micro-method of measuring ‘D-’ and ‘C-’ antigen contents of poliovirus preparations is described. The D-antigen of poliovirus is almost certainly the component of the virus involved in eliciting neutralizing antibodies, and the D-antigen assay thus becomes a simple in vitro method for assessing the antigenic potency of poliovaccines and for investigating the influence of various factors upon the antigen. The value of the technique in following the concentration and purification of poliovirus preparations is illustrated in the studies reported in the accompanying paper by Fantes (1962). The results of experiments designed to test the validity of the idea that D-antigen is the antigen eliciting neutralizing antibodies are discussed by Beale (1961).

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