The present invention provides an attenuated African Swine Fever (ASF) virus which lacks a functional version of the following genes: multigene-family 360 genes 9L, 10L, 11L, 12L, 13L and 14L; and multigene-family 505 genes 1R, 2R, 3R and 4R. The invention further provides an attenuated African Swine Fever (ASF) virus which lacks a functional version of the DP148R gene. The present invention also provides a vaccine comprising such an attenuated virus and its use to prevent ASF. Further, the invention relates to intranasal administration of an attenuated ASF virus.