The study authors noted that Haemophilus influenza type b was alone in lower protective rates in the preterm infants after the booster shot compared to healthy infants.
Preterm infants with routine vaccination schedules during their first year of life achieve protective antibody levels comparable to term infants after the primary series and the booster shot, according to a paper published in JAMA.
Investigators from the Netherlands compared preterm infants to healthy control infants in order to evaluate the immunogenicity of routine vaccinations administered to preterm infants. The investigators recruited 296 infants from 8 hospitals across the Netherlands between October 2015 and October 2017 and used 66 healthy control infants for their study. The study authors categorized infants in their first year of life into 3 gestational age groups: less than 28, 28 to less than 32, and 32 to 36 weeks. The babies were followed up with throughout their first year of life, until as late as October 2018, the study authors noted.
The vaccinations were administered in all infants according to the normal practice, the study authors said. The vaccines for diphtheria-tetanus toxoids-acellular pertussis-inactivated poliomyelitis-Haemophilus influenza type b-and hepatitis B was administered at 6 to 9 weeks, 3 months, 4 months, and 11 months, which is aligned with the national program in the Netherlands.
The babies in the study were 56% male with a mean gestational age of 30 weeks, the study authors noted. The study authors also said preterm infants have an increased susceptibility to infections due to decreased transfer of protective maternal antibodies, as well as a possible relative immaturity of the immune system compared to term babies.
A total of 220 preterm infants completed blood samples pre-vaccination, 1 month post-vaccination, and 1 month after the booster, the investigators said.
The study authors found that in all 3 preterm categories, the mean immunoglobulin G (IgG) levels for the different vaccine antigens prior to vaccination were low (between 1.5% and 54.9%). The pre-vaccination concentrations were lowest in the group with gestational age less than 28 weeks, and significantly lower for almost all antigens compared to the other 2 categories, the study authors wrote.
After the primary series of vaccination, the investigators found protective antibody levels against pertussis toxin, diphtheria toxoid, and tetanus toxin in between 93% and 100% of the preterm infants. Furthermore, the level of diphtheria toxin antibodies was greater than 99% across all preterm groups and did not differ from control infants, the study authors continued.
Haemophilus influenza type b protective antibodies were significantly lower in the preterm infants compared to the control infants (40% vs. 83%, respectively), the investigators said. The levels were lowest in the group with the shortest gestational age (34%).
After the booster vaccinations, nearly all of the preterm infants reached protective antibody status for all antigens, except for Haemophilus influenza type b, for which the study authors said levels were as follows: 88% in the overall preterm infants group; 87% in the group aged between 28 and 32 gestational weeks (lower than the group aged 32 to 36 gestational weeks as well as term infants).
“Among preterm infants, administration of routine vaccinations during the first year of life was associated with protective antibody levels against most antigens in the majority of infants after the primary series and booster, except for Haemophilus influenzae type b,” the study authors concluded, adding that it is possible to generalize these results across preterm infants in similar communities. “However, antibody concentrations were generally lower among preterm infants compared with historical controls.”