Vaccinations in Premature Infants

Abstract and Introduction

Abstract

Infections are more common and generally more severe in neonates and young children than in older children and adults, mainly because immune defenses are functionally impaired in early life. The seriousness of the infectious problems of premature infants (PIs) is proportional to how premature they are, but irrespective of this, they are more serious than those of full-term infants because their immune system is compromised to a greater extent. This review analyzes our knowledge of the characteristics of the developing immune system, the impact of possible impairments on immunization, the real response of PIs to vaccines and the safety and tolerability of different vaccines. Overall, the data indicate that PIs should follow the same vaccination schedule as that generally used for full-term infants, without correcting for prematurity and regardless of birthweight. However, there is an urgent need for further studies concerning the use of recently marketed vaccines and those that will be marketed in the near future.

Introduction

Infections are more frequent and generally more severe in neonates and younger children than in older children and adults, mainly because immune defenses are functionally impaired in early life.^[1,2] Skin and external barriers mature at different rates compared with elements of the innate response and bridging functions. However, all these components are immature at birth and, as the immune system does not fully mature for several months, children remain at higher risk of infections than adults for a long time after delivery.^[2] The seriousness of the infectious problems of premature infants (PIs) is proportional to how premature they are, but irrespective of this they are more serious than those of full-term infants (FTIs) because their immune system is compromised to a greater extent.^[2] Consequently, the prevention of infections in PIs through the use of all effective methods is recommended by health authorities throughout the world.

In terms of active immune prevention, it is generally indicated that PIs should be given vaccines following the same schedule as that generally used in FTIs, without correcting for prematurity and regardless of birthweight.^[3,4] However, despite this, the routine immunization of PIs is often delayed because many pediatricians think that their impaired immune system can significantly condition their response to vaccine antigens and reduce the protective effect of vaccination. Furthermore, even when doubts regarding the immunogenicity of vaccines in PIs are dispelled, a further limitation is the fear that the vaccines may not be completely safe or well tolerated and may lead to severe adverse events.^[3,4]

This review will analyze our knowledge of the characteristics of the developing immune system, the impact of possible impairments on immunization, the real response of PIs to vaccines and the safety and tolerability of different vaccines. All these data can help pediatricians decide how and when to offer the best vaccine protection to the PIs, reducing their risk of vaccine-preventable diseases.