Re-thinking yellow fever vaccines: fighting old foes with new generation vaccines

YF17D-vectored Ebola vaccine candidate protects mice against lethal surrogate Ebola and yellow fever virus challenge

Ebola virus (EBOV) and related filoviruses such as Sudan virus (SUDV) threaten global public health. Effective filovirus vaccines are available only for EBOV, yet restricted to emergency use considering a high reactogenicity and demanding logistics. Here we present YF-EBO, a live YF17D-vectored dual-target vaccine candidate expressing EBOV glycoprotein (GP) as protective antigen. Safety of YF-EBO in mice was further improved over that of parental YF17D vaccine. A single dose of YF-EBO was sufficient to induce high levels of EBOV GP-specific antibodies and cellular immune responses, that protected against lethal infection using EBOV GP-pseudotyped recombinant vesicular stomatitis virus (rVSV-EBOV) in interferon-deficient (Ifnar^-/-) mice as surrogate challenge model. Concomitantly induced yellow fever virus (YFV)-specific immunity protected Ifnar^-/- mice against intracranial YFV challenge. YF-EBO could thus help to simultaneously combat both EBOV and YFV epidemics. Finally, we demonstrate how to target other highly pathogenic filoviruses such as SUDV at the root of the 2022 outbreak in Uganda.

Recent Developments in Vaccines against Flaviviruses and Alphaviruses

In the twenty-first century, newly emerging viruses which are mostly zoonotic or vector-borne have continuously threatened public health and caused outbreaks of global concern [...].

A phase I clinical study to assess safety and immunogenicity of yellow fever vaccine

Yellow fever, a mosquito-borne flavivirus infection, is an important public health problem in Africa and Latin America. A Yellow Fever vaccine (YFV) was developed and tested in a study in India. This was a Phase I, open-label, randomized, controlled study where healthy adults received SII YFV intramuscularly (SII YFV IM), SII YFV subcutaneously (SII YFV SC) or STAMARIL^® (Sanofi-Pasteur) in 1:1:1 ratio. They were followed for solicited reactions for 10 days and unsolicited events for 28 days and serious adverse events for 3 months. YF-neutralizing antibodies were measured at baseline and on Days 10, 14, 28. A total of 60 adults were enrolled in the study. The proportion of participants with solicited reactions was 10%, 40%, and 25% in SII YFV SC, SII YFV IM, and STAMARIL^® arms, respectively. No causally related unsolicited events or any serious adverse event was reported. After vaccination, the seroconversion was 94.44%, 100%, and 100%, in the three arms respectively. The post-vaccination geometric mean titers were similar in the study arms. The new YFV was found safe and immunogenic by IM as well as SC routes. The vaccine can be tested in further phases of clinical studies.

Vector-Borne Viral Diseases as a Current Threat for Human and Animal Health—One Health Perspective

Over the last decades, an increase in the emergence or re-emergence of arthropod-borne viruses has been observed in many regions. Viruses such as dengue, yellow fever, or zika are a threat for millions of people on different continents. On the other hand, some arboviruses are still described as endemic, however, they could become more important in the near future. Additionally, there is a group of arboviruses that, although important for animal breeding, are not a direct threat for human health. Those include, e.g., Schmallenberg, bluetongue, or African swine fever viruses. This review focuses on arboviruses and their major vectors: mosquitoes, ticks, biting midges, and sandflies. We discuss the current knowledge on arbovirus transmission, ecology, and methods of prevention. As arboviruses are a challenge to both human and animal health, successful prevention and control are therefore only possible through a One Health perspective.

Flavivirus vaccines: Virus-like particles and single-round infectious particles as promising alternatives

The genus flavivirus of the Flaviridae family includes several human pathogens, like dengue, Zika, Japanese encephalitis, and yellow fever virus. These viruses continue to be a significant threat to human health. Vaccination remains the most useful approach to reduce the impact of flavivirus fever. However, currently available vaccines can induce severe side effects or have low effectiveness. An alternative is the use of recombinant vaccines, of which virus-like particles (VLP) and single-round infectious particles (SRIP) are of especial interest. VLP consist of the virus structural proteins produced in a heterologous system that self-assemble in a structure almost identical to the native virus. They are highly immunogenic and have been effective vaccines for other viruses for over 30 years. SRIP are promising vaccine candidates, as they induce both cellular and humoral responses, as viral proteins are expressed. Here, the state of the art to produce both types of particles and their use as vaccines against flaviviruses are discussed. We summarize the different approaches used for the design and production of flavivirus VLP and SRIP, the evidence for their safety and efficacy, and the main challenges for their use as commercial vaccines.

Predictive Markers of Immunogenicity and Efficacy for Human Vaccines

Vaccines represent one of the major advances of modern medicine. Despite the many successes of vaccination, continuous efforts to design new vaccines are needed to fight "old" pandemics, such as tuberculosis and malaria, as well as emerging pathogens, such as Zika virus and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Vaccination aims at reaching sterilizing immunity, however assessing vaccine efficacy is still challenging and underscores the need for a better understanding of immune protective responses. Identifying reliable predictive markers of immunogenicity can help to select and develop promising vaccine candidates during early preclinical studies and can lead to improved, personalized, vaccination strategies. A systems biology approach is increasingly being adopted to address these major challenges using multiple high-dimensional technologies combined with in silico models. Although the goal is to develop predictive models of vaccine efficacy in humans, applying this approach to animal models empowers basic and translational vaccine research. In this review, we provide an overview of vaccine immune signatures in preclinical models, as well as in target human populations. We also discuss high-throughput technologies used to probe vaccine-induced responses, along with data analysis and computational methodologies applied to the predictive modeling of vaccine efficacy.