Preparation and anti-influenza A virus activity of κ-carrageenan oligosaccharide and its sulphated derivatives

► κ-Carrageenan oligosaccharide KCO and its sulphated derivative KCO-S were prepared. ► KCO and KCO-S could effectively inhibit IAV multiplication in vitro. ► KCO and KCO-S could improve survival and decrease viral titres in IAV-infected mice. ► The antiviral effect of KCO and KCO-S does not seem to be dependent on interferon.