Persistence of Vaccine-Induced Immunity in Preschool Children: Effect of Gestational Age.

BACKGROUND A program of immunization that ensures optimal development of acquired immunity should be carried out in all healthy newborns. The aim of the present study was to verify, at 2.5-3 years after the last dose of basic vaccination, if preschool children who have been delivered preterm and at term differ in their levels of post-vaccination protective antibodies. MATERIAL AND METHODS Humoral response was assessed in 352 children (mean age: 5.22±0.34 years) who received a series of obligatory vaccinations in the period from birth to 2.5-3 years of age. Antibodies (in IgG class) against vaccine antigens - diphtheria (D), tetanus (T), pertussis (P), Haemophilus influenzae type b (Hib), poliomyelitis (IPV), measles, mumps, and rubella (MMR) - were measured using ELISA. The level of antibodies against hepatitis B (HBV) was assessed by chemiluminescence. RESULTS All children had been immunized according to the Polish National Vaccination Program. The group of 352 children eligible for the study included 46 (13.1%) preschoolers delivered preterm (32-36 weeks of gestation), and 306 (86.9%) born at term (37-42 weeks of gestation). All children maintained seroprotective antibody levels against polioviruses type 1, 2, and 3 (>12 mIU/mL), and against measles antigens (>300 U/mL). No statistically significant differences were found in the proportions of preschoolers born preterm and at term who were seroprotected against other vaccine antigens. CONCLUSIONS Among preschool children who were immunized according to chronological age, those we were born late preterm do not seem to differ in vaccine-induced immunity from those who were born full-term.