The non-specific effects of maternal immunization on birth outcomes: The evidence, mechanisms, and the implications

Preterm birth (PTB) and stillbirth remain two of the most important causes of death, morbidity, and disability in childhood. Despite efforts to reduce PTB and stillbirth worldwide, rates of these adverse outcomes remain persistently elevated, independent of income setting. There is an urgent need for more effective interventions to reduce associated neonatal and early childhood morbidity and mortality. Maternal vaccines are a well-established strategy used for prevention of pathogen-specific disease in mothers and infants through transplacental antibody transfer. Beyond these pathogen-specific benefits, some studies have also identified non-specific effects (NSEs) of maternal vaccination protecting against several adverse birth outcomes, including PTB and stillbirth. This paper will review the evidence supporting the NSEs of maternal vaccination on birth outcomes, describe the possible underlying mechanisms, outline the research gaps, and summarize the significance from a global health perspective.