Safety of Hepatitis B Vaccines (Monovalent or as Part of Combination) in Preterm Infants: A Systematic Review

Introduction: The World Health Organization (WHO) recommends vaccination against hepatitis B as soon as possible following birth for all infants, regardless of prematurity. Hepatitis B vaccination at birth is clearly justified, represents a crucial step in the global control of perinatally acquired hepatitis B and there are no safety concerns in infants born at term. However, there is limited information on the safety of the hepatitis B vaccine in preterm infants, whose immune responses and morbidity risk differ from those in infants born at term. Objectives: The objectives of this paper are to systematically review the literature regarding the safety and risk of adverse events following immunisation (AEFIs) associated with the administration of the hepatitis B vaccine (monovalent or as part of a combination vaccine) to preterm infants. Methods: We performed a search for relevant papers published between 1 January 2002 and 30 March 2023 in the Ovid MEDLINE, Ovid Embase, Cochrane Central Register of Controlled Trials and CINAHL Plus databases. Two authors independently reviewed and analysed each article to include in the systematic review. Narrative synthesis is presented. Results: Twenty-one relevant papers were identified and included in this systematic review. The vast majority of data pertained to multi-antigen (combination) vaccine preparations and vaccination episodes from 6 weeks of age onwards. We found no publications investigating the timing of the birth dose of the hepatitis B vaccine, and AEFI reporting was exclusively short-term (hours to days following administration). There was substantial variability in the reported rate of AEFIs between studies, ranging from 0% to 96%. Regardless of frequency, AEFIs were mostly minor and included injection site reactions, temperature instability and self-limiting cardiorespiratory events. Six studies reported serious adverse events (SAEs) such as the requirement for escalation of respiratory support. However, these occurred predominantly in high-risk infant populations and were rare (similar to 1%). Using the Grading of Recommendations, Assessment, Development, and Evaluations (GRADE) approach, the certainty of evidence was assessed as very low. Conclusions: Despite substantial variability between the relatively small number of published studies in terms of cohort selection, definitions, vaccine preparations and reporting, hepatitis B-containing vaccines (mostly as combination vaccines) appear to be relatively well tolerated in preterm infants from 6 weeks of age. Research focusing on the safety of hepatitis B vaccine in preterm infants specifically within 7 days of birth is lacking, particularly regarding long-term morbidity risk. Further research in this area is required.