Dr. Carl T. D'Angio and colleagues, from the University of Rochester, New York, compared the immune response of 16 former extremely preterm infants and 16 age-matched full-term controls at 7 years. All children had received their routine childhood immunizations at the appropriate chronological ages. The researchers measured antibodies to Haemophilus influenzae type b polyribosylribitol phosphate (Hib-PRP), tetanus, pertussis, diphtheria, polio, and hepatitis B.

The full-term group had higher antidiphtheria geometric mean titers (GMT) than the preterm group. Protective diphtheria titers (greater than 0.10 IU/mL) were found in all of the full term and 13 of the preterm children. Full-term children had tetanus GMT of 4.22 IU/mL, compared with 1.99 IU/mL in the preterm group. Protective tetanus titers (greater than 0.01 IU/mL) were found in all the children.

Pertussis titers were similar in both groups of children. The full-term group had higher Hib-PRP GMT than the preterm group, at 3.21 mcg/mL and 1.41 mcg/mL, respectively (p = 0.03). "All children had anti-PRP of at least 0.15 mcg/mL," the team notes. Twelve of the16 full-term children and 10 of the 16 preterm children had levels at least 1.0 mcg/mL.

They observed no differences in polio serotype 1 and 2 GMT between groups. Protective titers were found in all children. The full-term group had polio serotype 3 GMT of 59 Karber units, compared with 24 Karber units for preterm children. Protective titers were observed in all full-term children and 12 preterm children.

"Among children who had received hepatitis B vaccine, GMT were similar in full-term and preterm children...and similar proportions of children...had protective HBsAb titers (greater than 10 mIU/mL)," Dr. D'Angio and colleagues report.

Overall, "children who were born extremely prematurely [at 6.5 months or earlier] still get good levels of antibody (protection) from routine infant vaccines," Dr. D'Angio told Reuters Health.

"These findings support the American Academy of Pediatrics' general recommendation to immunize premature infants in the same way as one would immunize full-term infants," he continued. "However, the fact that premature infants' antibody levels are still somewhat lower than full-term babies' levels all the way out to 7 years implies that there may be some important, basic differences in the immune system if a baby is born early."

"Premature infants are at higher risk from vaccine preventable diseases," he added, "so it's particularly important for them to be immunized fully and on time."

Pediatrics 2002;109:498-504.