Immune response of neonates to oral poliomyelitis vaccine.

881 Immune response of neonates to oral poliomyelitis vaccine In the conventional schedule of immunisation infants are given three doses of oral poliomyelitis vaccine starting at, or after, 6 to 8 weeks of age. In the new pulse immunisation strategy three doses of oral poliomyelitis vaccine are given in annual cycles to children under 24 months of age.' I carried out a study to see whether a lower age limit could be established in this programme. Neonates were given one dose of oral poliomyelitis vaccine followed by second and third doses at intervals of four weeks. The seroconversion response in the neonates was as good as the response in older infants, indicating that immunisation may be started in the neonatal period. I studied 180 neonates and infants with parental consent. The first dose of oral poliomyelitis vaccine was given to groups of 30 infants at 7, 14, 21, 28, 35, and 42 days (one day) of age. Second and third doses were given at intervals of four weeks. The vaccine was tested and found to be fully potent. At least 30 minutes was allowed between administration of the vaccine and breast feeding. Capillary blood was collected immediately before giving the first dose of the vaccine and four weeks after the last dose. The second sample of blood was collected from only 139 infants. The paired serum samples were tested together in doubling dilutions from 1/8 to 1/1024 for poliovirus neutralising antibodies as described previously.2 The second serum sample was collected 12 weeks after the first. As the half life of maternal antibody in the infant's circulation is less than four weeks the persisting maternal antibody titre in the second serum sample would be lower than that in the first by a factor of eight or more. A fourfold or higher titre than the expected residual maternal antibody titre in the second serum sample was taken to indicate the infant's immune response (seroconversion) to the three doses of oral poliomyelitis vaccine.2 3 The table shows the frequency of the antibody response in the neonates and infants to three doses of poliomyelitis vaccine according to age at the start of immunisation. It also compares the antibody response of infants aged from 6 to 20 weeks with maternal antibody with that of infants aged from 6 to 51 weeks without maternal antibody from a previous study.2 The seroconversion response to the three types …