Preterm Immune System Development and Response to Immunization

To be eligible to participate in this study, a preterm infant must meet all following criteria: * Preterm infant born at gestational age less than 32 weeks (whose mothers did or did not receive a T dap vaccination during pregnancy) * Parents/ guardians must have sufficient understanding of the Dutch language To be eligible to participate in this study, a healthy full-term infant must meet all following criteria: * healthy full-term infant whose mother received a Tdap vaccination during pregnancy * Parents/ guardians must have sufficient understanding of the Dutch language To be eligible to participate in this study, a mother must meet all following criteria: \- Mother of preterm or health full-term infant who are participating in the study Exclusion Criteria: * Parents/guardians of the infant are not able or willing to provide informed consent * Infant with congenital anomaly which are more likely to cause adverse effects after immunization (for example hemodynamically significant congenital heart defect) * Infant with a (possible) HIV infection or immunodeficiency * Maternal use of immunosuppressive drugs during pregnancy