THE RELATIONSHIP OF MATERNAL ANTIBODY, BREAST FEEDING, AND AGE TO THE SUSCEPTIBILITY OF NEWBORN INFANTS TO INFECTION WITH ATTENUATED POLIOVIRUSES

1. Over 1,000 infants were fed attenuated polioviruses during the first 3 months of life and susceptibility to infection with these agents was shown to be related to dose of virus, titer of maternal antibody, method of milk feeding, and age at vaccination. 2. Larger doses of virus elicited a response in a high proportion of infants, but even the smallest dose employed was of nearly optimal effectiveness in infants with little or no maternal antibody. 3. No significant differences between the 3 types of polioviruses were observed other than those which could be related to differences in maternal antibody titer for the 3 types. 4. Maternal antibody had a direct relationship to the incidence of infection, particularly in breast-fed babies and in bottle-fed infants vaccinated on the first day of life. 5. Human milk contains poliovirus neutralizing substances (probably antibody but not specifically characterized) in concentrations related to the antibody titer in the mother's serum. However, a number of significant discrepancies between the antibody content of the serum and milk or colostrum were observed. It is postulated that infection is prevented by neutralization of the virus in the lumen of the infant's gut. 6. Susceptibility of bottle-fed babies increases rapidly during the first three days of life, but remains relatively unchanged thereafter. A reasonable hypothesis to explain this phenomenon is that maternal antibody in the infant's gut, whether from ingested amniotic fluid or by leakage from his circulation into the intestine, inactivates virus given on the first few days of life, but not later.