Vaccine
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Dengue is a significant threat to public health worldwide. Currently, there are no licensed vaccines available for dengue. Takeda Vaccines Inc. is developing a live, attenuated tetravalent dengue vaccine candidate (TDV) that consists of an attenuated DENV-2 strain (TDV-2) and three chimeric viruses containing the prM and E protein genes of DENV-1, -3 and -4 expressed in the context of the attenuated TDV-2 genome backbone (TDV-1, TDV-3, and TDV-4, respectively). ⋯ In addition, TDV induced CD8(+) T cell responses to the non-structural NS1, NS3 and NS5 proteins of DENV. TDV has been also shown to be generally well tolerated and immunogenic in a Phase 2 clinical trial in dengue endemic countries in adults and children as young as 18 months. Additional clinical studies are ongoing in preparation for a Phase 3 safety and efficacy study.
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Sanofi Pasteur has developed a recombinant, live-attenuated, tetravalent dengue vaccine (CYD-TDV) that is in late-stage development. The present review summarizes the different steps in the development of this dengue vaccine, with a particular focus on the clinical data from three efficacy trials, which includes one proof-of-concept phase IIb (NCT00842530) and two pivotal phase III efficacy trials (NCT01373281 and NCT01374516). Earlier studies showed that the CYD-TDV candidate had a satisfactory safety profile and was immunogenic across the four vaccine serotypes in both in vitro and in vivo preclinical tests, as well as in initial phase I to phase II clinical trials in both flavivirus-naïve and seropositive individuals. ⋯ The end of the active phases in these studies completes more than a decade of development of CYD-TDV, but considerable activities and efforts remain to address outstanding scientific, clinical, and immunological questions, while preparing for the introduction and use of CYD-TDV. Additional safety observations were recently reported from the first complete year of hospital phase longer term surveillance for two phase 3 studies and the first and second completed years for one phase 2b study, demonstrating the optimal age for intervention from 9 years. Dengue is a complex disease, and both short-term and long-term safety and efficacy will continue to be addressed by ongoing long-term follow-up and future post-licensure studies.
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Dengue viruses (DENV) currently infect approximately 400 million people each year causing millions to seek care and overwhelming the health care infrastructure in endemic areas. Vaccines to prevent dengue and therapeutics to treat dengue are not currently available. The efficacy of the most advanced candidate vaccine against symptomatic dengue in general and DENV-2 in particular was much lower than expected, despite the ability of the vaccine to induce neutralizing antibody against all four DENV serotypes. ⋯ The Walter Reed Army Institute of Research (WRAIR) is developing a DHIM the goal of which is to identify DENV that cause symptomatic dengue fever. WRAIR has evaluated seven viruses and has identified two that meet dengue fever criteria. Both of these models may be very useful in the evaluation and down-selection of candidate dengue vaccines and therapeutics.
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Large outbreaks of zoonotic influenza A virus (IAV) infections may presage an influenza pandemic. However, the likelihood that an airborne-transmissible variant evolves upon zoonotic infection or co-infection with zoonotic and seasonal IAVs remains poorly understood, as does the relative importance of accumulating mutations versus re-assortment in this process. Using discrete-time probabilistic models, we determined quantitative probability ranges that transmissible variants with 1-5 mutations and transmissible re-assortants evolve after a given number of zoonotic IAV infections. ⋯ This may result in the evolution of a full transmissible genotype along short chains of contact transmission. Although co-infection with zoonotic and seasonal IAVs was shown to be a rare event, it consistently resulted in high viral loads of re-assortants, which may facilitate their onward transmission among humans. The prevention or limitation of zoonotic IAV infection in immunocompromised and contact individuals, including health care workers, as well as vaccination against seasonal IAVs-limiting the risk of co-infection-should be considered fundamental tools to thwart the evolution of a novel pandemic IAV by accumulation of mutations and re-assortment.