The SARS-CoV-2 KP.3.1.1 lineage is currently the dominating lineage on several continents. In parallel, the XEC lineage, a recombinant of KS.1.1 and KP.3.3, is on track of becoming the next dominant lineage in Europe and North America. Here we performed a rapid virological characterisation of the XEC lineage and studied the impact of JN.1 mRNA booster vaccination on KP.3.1.1 and XEC neutralisation.