Birth represents a relatively dramatic transition from an environment with a low microbial burden to one abundant in commensal and potentially pathogenic challenges that the neonatal immune system must be able to respond to. Immune responses in preterm and term neonates differ from those of adults, generally being characterized as diminished, tolerant or Th skewed although we must be mindful that these are highly evolved, stage of life appropriate responses.Efforts to clarify the phenotypes and mechanisms prevalent at this time are ongoing so that we can better understand the significance of differences at this stage of development for long-term health.The need to understand how the neonatal immune response differs to that of adults is driven by the mortality and morbidity associated with infection and sepsis in newborns and infants and the need for protective vaccine responses that can mitigate these.

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