Background: The live attenuated dengue virus type 4 (DEN-4) vaccine candidate virus rDEN4 Delta 30 was previously found to be safe and immunogenic at a dose of 10(5) plaque-forming units (pfu).
Methods: In a follow-up placebo-controlled phase 2 clinical trial, rDEN4 Delta 30 was administered as a single inoculation to 3 separate dose cohorts (10(3) pfu, 10(2) pfu, or 10(1) pfu), for further evaluation. Each dose cohort consisted of 20 vaccinees and 4 placebo recipients. Volunteers were monitored closely for adverse events, and serum was collected on study days 28 and 42 for determination of neutralizing antibody titer.
Results: The vaccine was well tolerated at all doses studied. The most common adverse events observed were a transient asymptomatic rash in >50% of vaccinees and a mild neutropenia in approximately 20% of vaccinees. No vaccinee developed a dengue-like illness. The vaccine was highly infectious and immunogenic, with 95%-100% of vaccinees in each dose cohort developing a >/=4-fold increase in titers of serum neutralizing antibodies against DEN-4.
Conclusions: The rDEN4 Delta 30 vaccine is safe and induced an antibody response that was broadly neutralizing against genotypically diverse DEN-4 viruses. It is a promising vaccine candidate for inclusion in a tetravalent dengue vaccine formulation.