Immune response to tetanus booster in infants aged 15 months born prematurely with very low birth weight.

OBJECTIVES To compare humoral and cellular immune responses to tetanus booster vaccination in infants born prematurely with those born at full term and identify factors associated with the humoral response. METHODS A prospective study was carried out on children born prematurely and with a birth weight <1500g and with infants born at full term. At 15 months (pre-vaccination) and 18 months (post-vaccination), anti-tetanus antibodies were measured by ELISA; the intracellular interferon-gamma percentages of CD4+ T and CD8+ T cells after in vitro stimulation with tetanus toxoid were determined by flow cytometry. Chi-squared or Fisher's exact test was used to compare categorical variables. Student's t-test or Mann-Whitney test was used to compare numerical variables. Regression analysis was performed to determine factors associated with humoral immunity. Statistical significance was considered if p<0.05. RESULTS Sixty-four premature and 54 full-term infants were studied. The proportion of children immune against tetanus at 15 and 18 months was similar in both groups. The geometric mean of the antibodies was lower among the premature children at 15 months (p=0.025) and was similar in both groups at 18 months (p=0.852). The percentages of CD4+ and CD8+ T cells expressing intracellular IFN-γ were similar in both groups at 15 and 18 months. Gestational age <32 weeks was associated with a reduction of -0.116IU/mL in the level of antibodies at 15 months. Breastfeeding >6 months was associated with a 3.5-fold greater chance of optimal protective (≥0.1IU/mL) antibody level against tetanus at 15 months and an increase of 0.956IU/mL in the level of antibodies at 18 months. CONCLUSIONS Humoral and cellular response following a tetanus booster was similar in both groups. Premature infants exhibited lower levels of anti-tetanus antibodies at 15 months of age, with the lowest levels in those born at a gestational age of less than 32 weeks. Breastfeeding was associated with greater levels of antibody against tetanus.