The human respiratory syncytial virus (hRSV) is the main etiologic agent of severe lower respiratory tract infections that affects young children throughout the world, associated with significant morbidity and mortality, becoming a serious public health problem globally. Up to date, no licensed vaccines are available to prevent severe hRSV-induced disease and the generation of safe-effective vaccines have been a challenging task, requiring constant biomedical research aimed to overcome this ailment. Among the difficulties presented by the study of this pathogen, arises the fact that there is no single animal model that resembles all aspects of the human pathology, which is due to the specificity that this pathogen has for the human host. Thus, for the study of hRSV, different animal models might be employed, depending of the goal of the study. Of all the existing models, the murine model has been the most frequent model of choice for biomedical studies worldwide and has been of great importance at contributing to the development and understanding of vaccines and therapies against hRSV. However, several additional different models for studying hRSV, such as other rodents, mustelids, ruminants and non-human primates have been explored, offering advantages over the murine model. In this review, we discuss the various applications of animal models to the study of hRSV-induced disease, the advantages and disadvantages of each model, highlighting the potential of each model to elucidate different features of the pathology caused by the hRSV infection.

Background:Mycobacterium bovis Bacillus Calmette-Guérin (BCG) is a live attenuated vaccine mainly administered to newborns and used for over 100 years to prevent the disease caused by Mycobacterium tuberculosis (M. tb). This vaccine can induce immune response polarization towards a Th1 profile, which is desired for counteracting M. tb, other mycobacteria, and unrelated intracellular pathogens. The vaccine BCG has been used as a vector to express recombinant proteins and has been shown to protect against several diseases, particularly respiratory viruses. Methods: BCG was used to develop recombinant vaccines expressing either the Nucleoprotein from SARS-CoV-2 or Andes orthohantavirus. Mice were immunized with these vaccines with the aim of evaluating the safety and immunogenicity parameters. Results: Immunization with two doses of 1 × 10⁸ CFU or one dose of 1 × 10⁵ CFU of these BCGs was safe in mice. A statistically significant cellular immune response was induced by both formulations, characterized as the activation of CD4⁺ and CD8⁺ T cells. Stimulation with unrelated antigens resulted in increased expression of activation markers by T cells and secretion of IL-2 and IFN-γ, while increased secretion of IL-6 was found for both recombinant vaccines; all of these parameters related to a trained immunity profile. The humoral immune response elicited by both vaccines was modest, but further exposure to antigens could increase this response. Conclusions: The BCG vaccine is a promising platform for developing vaccines against different pathogens, inducing a marked antigen-specific immune response.