A prospective cohort study was conducted in Italy to investigate the effects of breastfeeding on the risk for fever after routine immunisations. Mothers of infants (460) scheduled to receive routine immunisations were instructed on how to measure and record infant temperature on the evening of the vaccination and for the subsequent 3 days. The information about the incidence of fever was obtained by telephone on the third day after vaccination. The relative risk for fever in relation to the type of breastfeeding was estimated in multivariate analyses that adjusted for vaccine dose, maternal education and smoking, and number of other children in the household. The researchers found that fever was reported for 30 (25%), 48 (31%), and 94 (53%) of the infants who were being exclusively breastfed, partially breastfed, or not breastfed at all, respectively (P < .01). The protection conferred by breastfeeding persisted even when considering the role of several potential confounders. The researchers concluded that in this study, breastfeeding was associated with a decreased incidence of fever after immunizations.