1 Virus Laboratory, Ministry of Health, Tel Aviv-Yaffo, Israel
The antibody response of young infants after immunization with formalinized poliomyelitis vaccine was investigated. The infants were 1 to 6 months of age at the time of primary immunization. The effect of primary as well as booster immunization was studied by testing pre- and post-primary, and pre- and post-booster specimens of blood. Vaccine lots used for immunization were of high potency as judged from guinea pig antigenic extinction titers.
Prior to these tests the status of maternal antibody was determined in 594 infants, 0 to 6 months of age. These tests showed that at birth, 87 to 94% of infants have antibody for the three types of poliomyelitis virus, about 50% at the age of 3 months, and 11 to 16% at the age of 5 and 6 months.
For convenience of analysis of results, the infants were divided into three "age-groups": Group A consisted of infants 1 and 2 months of age, Group B, 3 and 4 months, and Group C, 5 and 6 months of age. To facilitate interpretation, the antibody response to primary immunization in Groups A and B was tested at the age of 6 months. Development of antibody after primary immunization was pronounced in all three groups. It was shown, however, that the greater the age at primary immunization, the better the response; the conversion rates and antibody titers in infants of Group C were higher than in Group B and these in turn higher than in Group A. With the vaccines employed, post-primary conversion rates in infants of Group C were 71, 98 and 53% for poliomyelitis virus types 1, 2 and 3, respectively, after a course of two inoculations, and 90, 100 and 85%, respectively, after three inoculations of vaccine. In all infants, the best response to the vaccines employed was to type 2 antigen, less to type 1 and poorest to type 3. Presence of maternal antibody seemed to interfere with active production of antibody.
The booster response was excellent in all infants studied. It was shown to be independent of age at primary immunization and of presence or absence of maternal antibody at the time when primary immunization had been carried out. Adequate primary immunization of infants, i.e. with antigen of high potency and large amount, either produces demonstrable antibody or "sensitizes" in such a way that a booster inoculation will promptly show presence of antibody.
Submitted on September 10, 1959