Factors that contribute to the survival of premature infants, such as the use of prenatal steroids in women at high risk of giving premature birth  and the use of postnatal corticosteroids
for the treatment of bronchopulmonary dysplasia , may also affect the immune response to vaccination in children born prematurely  and . According to Slack et al. , the production of anti-tetanus antibodies in premature infants with a gestational age of less than 32 weeks is negatively associated with the number of doses of prenatal corticosteroids. Robinson et al.  found that antibody levels following vaccination for tetanus, diphtheria and whooping cough were lower in children with bronchopulmonary Olaparib in vivo dysplasia treated with dexamethasone. Moreover, breastfeeding, less prevalent among premature infants, and nutritional status, which may be compromised in this population, are also involved in the immune response to vaccination  and . It is not known whether the compromised immune response to vaccination in premature infants is only related to vaccines administered in the first six months of PD0325901 concentration life. However, Kirmani et al.  reported lower antibody
levels following vaccination for diphtheria, tetanus toxoid, poliovirus, Haemophilus influenzae type b and hepatitis B in seven-year-old children born at a gestational age of less than 29 weeks and with a birth weight of less than 1000 g in comparison to children of the same age born at full term. The aims of the present study were to compare the humoral and cellular immune response to a tetanus booster vaccine at 15 months of age in infants born prematurely with those born at full term and to identify factors associated with humoral immune response. Specifically with regard to immune response, the concentration of anti-tetanus
antibodies and percentages of CD4+ T and CD8+ T cells expressing intracellular interferon-gamma after in vitro stimulation with tetanus toxoid were compared before and after the tetanus booster vaccination. The present prospective study was carried out between September 2007 and January 2010 and received MycoClean Mycoplasma Removal Kit approval from the Ethics Committee of the institution. All parents/guardians of the participants signed a statement of informed consent. The inclusion criteria were children aged 15 months, having received three doses of tetanus vaccine (at 2, 4 and 6 months of age) and not having yet received the tetanus booster vaccine. Participants were divided into two groups. The premature group included children born with a gestational age of less than 37 weeks and birth weight of less than 1500 g (very low birth weight preterm infants). These infants were assisted at the neonatal intensive care unit of the Federal University of São Paulo, SP, Brazil, where preterm infants with birth weight less than 1500 g were followed up at the multidisciplinary premature outpatient clinic of the institution.