The purpose of this investigation was to determine the influence of the dose of Sabin Type I attenuated oral poliovirus vaccine upon the response of newborn infants and to delineate further the factors which alter intestinal infection with this virus. In an earlier study,1 fewer newborn infants excreted virus after a single dose of vaccine than did babies 3 months of age. All of the newborns had received 107.5 TCD50* in 1 ml. of vaccine virus, a dose which is 100 times that recommended for older children and adults.2 Most of the newborns who failed to become infected were born to mothers with antibody titers of 256 or greater. In addition, infants who were breast fed did not appear to become infected so readily as did their bottle-fed peers, particularly when the titer of passive antibody was high.
In the previous experiment the dose of 10