Abstract
Rotavirus (RV) is the most common cause of childhood diarrhea worldwide, and several vaccines have been successfully developed to reduce the burden of disease. However, lower vaccine immunogenicity and efficacy in developing countries might be related to the virus-neutralizing activity of breast milk. We examined possible differences in breast milk antibody levels (total IgA antibody, RV-specific antibodies, and RV-neutralizing antibodies) between healthy mothers living in a rural area (n=145) and mothers living in an urban area (n=147) of Vietnam. Total IgA concentration was significantly higher in samples from mothers in the rural region than in samples from mothers in the urban region, whereas urban mothers had significantly higher RV-specific IgA antibody titers than did rural mothers. Neutralizing antibodies against RV strain G1P[8] were undetected in nearly one-half of the breast milk samples (45-48%), whereas the majority of the remaining samples had low antibody titers (2-16). Despite these low titers, the breast milk still reduced vaccine strain titers (2×10(6) plaque forming units/mL) up to 80% or more, even at a milk-to-virus ratio of 1:8. An increase in neutralizing anti-G1P[8] antibody titers (P<0.05) in rural infants over time suggests a continuous exposure to circulating RV. These results contribute to the understanding of the potential interference of breast milk with RV vaccine efficacy and immunogenicity in Vietnamese infants.