Risk and protective factors of acute respiratory infections in infants

Abstract

OBJECTIVE: To analyze the effectiveness of maternal pneumococcal polysaccharide vaccine and the risk and protective factors for acute respiratory infections in infants. METHODS: Nested cross-sectional study of a clinical trial evaluating children of 139 women selected in a public prenatal care unit in the municipality of São Paulo, Southeastern Brazil, from 2005 to 2006. Subjects were randomly assigned to three groups: non-immunized (n=46); immunized with pneumococcal polysaccharide vaccine in the last trimester of pregnancy (n=42); and immunized with the vaccine immediately after childbirth (n=45). Infants were followed up for infections presumably caused by pneumococcus at the age of three and six months and nasopharyngeal samples were collected. Risk factors such as smokers living in the same household, siblings and exclusive maternal breastfeeding were investigated. RESULTS: The pneumococcal polysaccharide vaccine did not provide protection against pneumococcus infections. However, exclusive maternal breastfeeding until the age of six months protected infants against respiratory infections (OR= 7.331). Pneumococcal nasopharyngeal colonization at the age of three or six months increased the likelihood of occurrence of respiratory infections (OR= 2.792). CONCLUSIONS: Exclusive breastfeeding for six months protects infants against presumably pneumococcal infections regardless of pneumococcal vaccination.