A synthetic mixture of human milk oligosaccharides (HMOs) consisting essentially of lacto-N-neotetraose (LNnT), lacto-N-tetraose (LNT), 2′-fucosyllactose (2′FL), 3′-O-sialyllactose (3′-SL), 6′-O-sialyllactose (6′-SL) either difucosyllactose (DFL) or 3-fucosyllactose (3-FL), preferably DFL, and optionally lactose. Said synthetic composition is useful for: treating or preventing viral and/or bacterial infection in a non-infant human; modulating the microbiota of a non-infant human; and/or improving the cognitive function of a non-infant human and as a pharmaceutical or nutritional composition.