Seven-year follow-up of vaccine response in extremely premature infants

Objective. To assess the immune response of 7-year-old former extremely preterm (PT) infants to routine childhood immunizations. Methods. Sixteen PT (less than 29 weeks and <1000 g) infants, followed since their primary immunizations at the recommended chronological ages, and 16 age-matched full-term (FT) control subjects were evaluated at 7 years of age. Antibodies to Haemophilus influenzae type b polyribosylribitol phosphate (Hib-PRP), tetanus, pertussis, diphtheria, polio, and hepatitis B (HBsAb) were measured. Results. The FT group had higher antidiphtheria geometric mean titers (GMT) than the PT group (1.07 vs 0.36 IU/mL). All FT and 13 of 16 PT had protective diphtheria antibody titers (> 0.1 IU/mL). The tetanus GMT were 4.22 IU/mL (FT) and 1.99 IU/mL (PT). All children had protective tetanus titers (> 0.01 IU/mL). Pertussis titers did not differ between FT and PT. Hib-PRP GMT were higher in FT than in PT (3.21 vs 1.41 mug/mL). All children had anti-PRP greater than or equal to 0.15 mug/mL; 12 of 16 FT and 10 of 16 PT had levels greater than or equal to1.0 mug/mL. Polio serotype 1 and 2 GMT were similar between groups, and all children had protective titers ( 8). Polio serotype 3 GMT were 59 (FT) and 24 (PT) Karber units; all FT and 12 of 16 PT had protective titers. Among children who had received hepatitis B vaccine, GMT were similar in FT and PT children (120 vs 186 mIU/mL, and similar proportions of children (11 of 16 FT and 12 of 14 PT) had protective HBsAb titers (> 10 mIU/mL). Conclusions. At 7 years of age, PT children had lower antibody titers to many vaccine antigens than FT children. However, most PT children maintained antibody titers in the protective range.