Implementation of mandatory vaccinations against diphtheria, tetanus and pertussis in preterm infants as part of the Polish Immunization Programme

Introduction
Children born before the 30 week of pregnancy, especially with extremely low birth weight, are to a large degree deprived of the protective level of antibodies normally conveyed by the mother, which makes them more prone to sepsis, pertussis, pneumococcal infections, and influenza. Preterm infants are more likely to be hospitalized due to a pertussis infection than full-term children with normal body weight. Meanwhile, the level of active prevention of infectious diseases is lower in the case of preterm infants than for infants born between the 37th and 40th week of pregnancy, since vaccinations are delayed all too often in the former group. Since 2009, preterm infants hospitalized at the neonatal ward of the University Hospital CMUJ for more than 42 days receive vaccinations against diphtheria, tetanus, pertussis and pneumococcal infections, in addition to routine BCG and HBV immunization. Active prevention of infec¬tious diseases in preterm infants hospitalized at this ward was carried out at the Infectious Diseases Clinic that is part of St. Louis Specialized Regional Children's Hospital in Cracow.

Research material and methodology
A group of preterm infants with birth weight below 1500 g was selected from a group of preterm infants registered at the Clinic and born before the 30th week of pregnancy in the period from September 2009 to September 2014. These criteria were met by 123 children. Fourteen children who did not receive the three doses of primary DTPa vaccinations either at the Clinic or at the neona¬tal wards were excluded. The gestational age at birth in the analyzed group 109 children ranged from 22 to 30 weeks, with a mean of 26.8 weeks. Birth weight ranged from 520 g to 1480 g; the mean weight was 953.4 g. The studied group of 109 patients was divided into two subgroups, the first consisted of 57 children who received their initial DTPa vaccinations at neonatal ward and the second were first administered DTPa vaccines at the Clinic. Of 109 children, only 14 (12.84%) were vaccinated on schedule. Sixty-one child¬ren (56%) received the DTPa-IPV-Hib-HBV hexavalent vaccine, while the remaining 48 children (44%) were vaccinated with DTPa. In subgroup vaccinated at the neonatal ward, the proportion of children who received the hexavalent vaccine was higher (73.7%) than in second subgroup, in which the polyvalent vaccine was administered to 36.5% of the children. There were no significant differences in terms of the time of the fast vaccination in subgroup vaccinated in the hospital setting. However, the time of the second vaccination at the Clinic was statistically significant. Children who had received the hexavalent vaccine received the second dose earlier. Both in subgroup vaccinated at the Clinic as well as across the entire studied group, statistically significant differences in the implementation of the Immunization Programme were found to be in favor of the children who had received the hexavalent vaccine. The geometric mean levels of tetanus toxoid-specific, diphtheria toxoid-specific, and pertussis-specific antibodies as well as anti HEts were all found to be sufficient to provide adequate protection. The children vaccinated in the hospital setting did not develop any adverse symptoms. Neither of the subgroups experienced any serious adverse events related to vaccination at the Clinic.

Conclusions
1. Even during prolonged hospitalization at a neonatal intensive care unit, immunization with the DTPa vaccine should be performed in addition to vaccination against tuberculosis and HBV. 2. DTPa-1PV-Hib-HBV hexavalent vaccines provide an optimal solution for the implementation of immunization schedules, especially in preterrn infants and - even more so - pretem infants with extremely low birth weight 3. Results from the monitoring of episodes of apnea, bradycardia and saturation levels before and after vaccination at the neonatal ward provide valuable information to the physician that continues vaccination as part of outpatient care.