Genetic stability of a dengue vaccine based on chimeric yellow fever/dengue viruses

► The CYD tetravalent dengue vaccine candidate is in clinical phase III. ► The 4 chimeric CYD vaccine viruses were fully sequenced throughout manufacturing. ► Complete genetic stability (no mutations) was seen from seed to bulk lots. ► At late amplification passages, rare incomplete nucleotide variations were detected. ► The in vivo emergence of mutant viruses after vaccination is highly unlikely.