The present invention relates to NS1 proteins or parts thereof of Flaviviruses, in particular of Dengue viruses useful for vaccination against said Flavivirus and against one or more other Flaviviruses. The invention further concerns the NS1 protein or parts thereof of one Dengue virus serotype, in particular serotype 2, useful for vaccination against Dengue viruses from all serotypes. The invention further concerns DNA comprising an expression cassette coding for a Flavivirus NS1 or parts thereof, vectors comprising said DNA and vaccines containing or expressing a Flavivirus NS1.