Breast-feeding and responses to infant vaccines: constitutional and environmental factors.

Neonates and nursing infants are special with regard to immune development and vulnerability to infectious diseases. Although breast-feeding is essential to modulate and prime immune defenses, vaccines (an interventional prophylaxis) are crucial to prevent and control infectious diseases. During nursing, the type of feeding influences infants' natural defenses (including gut colonization) and their response to vaccines, both through cell-mediated immunity and specific antibody production. Given the variety and combination of vaccine components (antigens and excipients, preservative thimerosal, and aluminum adjuvants) and route of administration, there is a need to examine the role of infant feeding practices in intended and nonintended outcomes of vaccination. Maternal factors related to milk constituents (nutrients and pollutants) and feeding practices can affect response to vaccines. Collectively, studies that compared type of feeding (or used breast-feeding-adjusted statistical models) showed significant influence on some vaccines taken during infancy. Nurslings deprived of the full benefit of breast-feeding could have altered immune responses affecting vaccine outcome. In the absence of studies elucidating neurodevelopment (including excitoxicity) and immunotoxicity issues, vaccination practices should promote and support breast-feeding. Thieme Medical Publishers 333 Seventh Avenue, New York, NY 10001, USA.