Objective:

To provide an up-to-date overview of the phenotype and function of the immune system in preterm infants compared with term infants, with a particular emphasis on the critical role of adaptive immunity in health outcomes.

Key Findings:

• Preterm infants exhibit phenotypic and functional immaturity in both innate and adaptive immune systems, impacting their vulnerability to infections.
• Antibody levels are reduced in preterm infants, affecting pathogen clearance and vaccine responses, with implications for clinical management.
• Rapid maturation of the immune system occurs during the first year of life, with differences from term infants becoming less pronounced, highlighting the need for ongoing monitoring.

Interpretation:

Recognizing the all-encompassing nature of immune immaturity in preterm infants is essential for developing integrated strategies to improve health outcomes, particularly in vaccination and infection prevention.

Limitations:

• The duration of adaptive immune immaturity and its effects on vaccination responses remain incompletely understood, which may affect clinical decision-making.
• Variability in immune responses may exist based on specific pathogens, complicating treatment approaches.

Conclusion:

The review provides a framework for understanding the immunologic mechanisms underlying the increased infection risk in preterm-born infants, emphasizing the need for targeted interventions to address immune immaturity.