Insufficient immune protection in preterm infants due to delayed or incomplete hexavalent vaccination

Abstract

Introduction: For preterm infants, a 3 + 1 schedule is recommended for hexavalent vaccinations during the first year. The aim of this study was to analyze completion and timeliness of vaccinations in preterm infants of 28 + 0 32+6weeksofgestationas part ofthe PRIMALstudy (PRimingof IMmunityAtthe beginning of Life) and the antibody responses to vaccination antigens. Methods: Plasma antibody-concentrations against poliomyelitis, Haemophilus influenzae type b (Hib), diphtheria and tetanus were determined using ELISA and evaluated with respect to their protectiveness. Results: Among 82 patients that were recruited, paired plasma samples on admission and at the one year follow up visit were available in 41 infants. In 17 infants, plasma samples were also collected at two months, prior to the first vaccination. Transplacental antibody transfer yielded protective antibody concentrations against the vaccine antigens in 66% (Hib) to 93% (tetanus) of the infants on admission andin24%(Polio) to50%(diphtheria) at 2months.Atthe one-year follow-up, all infants who received their vaccinations on time had complete immune protection. However, after one year, hexavalent vaccination wasincompletein30of41infants(73%). Amongincompletely vaccinatedinfants, the proportion lacking protective antibody concentrations ranged from 12% for diphtheria to 27% for polio. Conclusions: Due to insufficient adherence to vaccination recommendations, 42% of highly vulnerable preterm neonates were insufficiently protected against one or more vaccine-preventable diseases after one year. Efforts should be increased to improve adherence to the recommended 3 + 1 vaccination schedule in preterm infants.