ABSTRACT
SARS-CoV-2 infects humans by the use of the extracellular Spike protein (S) to attach to specific cell surface receptors. Due to its indispensable role, the S protein is a major target of virus neutralizing antibodies and has become a key antigen for vaccine candidates development. Recent improvements in mRNA vaccines act to increase protein translation, modulate innate and adaptive immunogenicity and improve delivery. mRNA vaccines are a new type of vaccine to protect against infectious diseases and were the first COVID-19 vaccines authorized worldwide. Relevant animal models are critical for a successful development of all SARS-CoV-2 vaccine candidates and are necessary to characterize the immune response induced by a SARS-CoV-2 vaccine candidate before moving into larger clinical studies, so as to address the theoretical risk for SARS-CoV-2 vaccine-induced disease enhancement. If vaccines are effective on disease severity and reduce hospitalizations, the question is whether vaccination reduces virus transmission. Even, protection against reinfection with SARS-CoV-2 has been observed in rhesus monkeys, who formed neutralising antibodies on initial exposure and a minimum neutralising antibody titre has been proposed, no formals studies have been conducted from a non-clin-ical or clinical point of view, assessing the effect of the vaccination on a potential reduction in transmission nor the transmission between individuals. This review provides an overview of the non-clinical data of the two different covid-19 RNA vaccines approved on the market, the different animal models studied as well as the virus transmission between individuals. The objective is to make a comparison of the results of the challenge study on Non Human Primates (NHP), analysing all criteria that can approach this activity on the transmission of the infection (i.e. Viral RNA in nasal and oropharyngeal swabs and bronchoalveolar lavage after vaccination, clinical signs,...) However, since SARS-CoV-2 is a novel pathogen, any surrogate endpoints identified in animal studies would ideally need validation in clinical trials to ensure that they adequately predict efficacy in humans.