Self-propagating, fusogenic blebs are produced from cells infected with a population of Venezuelan Equine Encephalitis virus replicon particles (VRP). The self-propagating, fusogenic nature of the blebs is derived from expression of heterologous genes encoding viral fusion proteins that are incorporated into the replication defective replicon particles. The resulting blebs can be harvested from supernatants of cells displaying severe cytopathic effects. The blebs are used to make immunogenic compositions and devise methods of immunizing mammals against paramyxoviruses such as parainfluenza virus type 3.