rDEN2/4Δ30(ME), a Live Attenuated Chimeric Dengue Serotype 2 Vaccine, is Safe and Highly Immunogenic in Healthy Dengue-Naïve Adults

rDEN2/4Δ30(ME) is an attenuated chimeric dengue virus in which the prM and E structural proteins of the DEN4 candidate vaccine rDEN4∆30 have been replaced by those of the prototypic DEN2 NGC virus. rDEN2/4Δ30(ME) was evaluated at a dose of 1,000 PFU in 20 healthy dengue-naive adult volunteers. Eight volunteers received placebo. Volunteers were monitored closely for adverse events and serum was collected for determination of the level and duration of viremia and neutralizing antibody response. The vaccine was well tolerated by all volunteers. The most common adverse events observed were a transient asymptomatic rash and mild neutropenia. All vaccinees seroconverted to DEN2 and maintained significant antibody titers throughout the six-month trial duration. Eleven vaccinees had vaccine virus recovered from the blood during the study. RNA derived from virus isolates obtained from viremic volunteers was sequenced for confirmation of retention of the ∆30 mutation in the 3´ UTR. The Δ30 mutation remained unchang...