Although flaviviruses cause a great deal of human suffering and economic loss, there is a shortage of effective vaccines. The present invention is directed toward vector stage replication-defective flaviviruses that are replication-defective in mosquito vectors that transmit them to humans. The replication-defective flaviviruses of the present invention demonstrate a limited ability to replicate in the vector organisms that transmit flaviviruses from one host to another. More specifically, the present invention is directed toward the construction and propagation of flaviviruses that possess 3'-noncoding regions altered in such a way as to prevent or severely limit viral reproduction in a vector organism. Not only is the dengue 1 mutant replication defective in mosquitoes, but it is also attenuated and immunogenic in monkeys. Moreover, it protects against challenge, thus it has strong potential as a dengue vaccine.