On May 31, 2024, Sanofi announced that its infant nasal spray respiratory syncytial virus attenuated live vaccine (RSVt vaccine, SP0125) has been approved for clinical research by the Drug Evaluation Center (CDE) of the National Medical Products Administration (NMPA) of China. This is the first children's vaccine in China to participate in international multicenter clinical trials (MRCT) since the implementation of the new version of the Drug Registration Management Measures in 2020. At the same time, the RSVt vaccine is also the world's first vaccine designed for infants and young children to prevent diseases caused by respiratory syncytial virus (RSV), providing protection for infants and young children aged 6 to 24 months. The full protection of infants and young children is the key to reducing the burden of respiratory syncytial virus disease in children. Synaptic virus is one of the most common viral pathogens causing acute upper respiratory tract infections (AURI) in infants and young children. Meanwhile, for some infants and young children, syncytial virus infection can develop into lower respiratory tract diseases, which is also the main reason for hospitalization. The mucosal immune response of the respiratory tract is an important pathway to resist virus invasion of the respiratory tract. Compared to systemic vaccination that only induces serum immunoglobulin G (IgG) response, nasal spray vaccine can induce serum IgG response and nasal mucosal immunoglobulin A (IgA) response, effectively blocking the infection and transmission of respiratory viruses. Research has shown that RSVt vaccines exhibit significant therapeutic effects in young children, inducing a broad and persistent immune response. Previously, the RSVt vaccine achieved positive results in global Phase I/II clinical trials. The data shows that the two doses of RSVt vaccine have similar tolerance to placebo and can induce 93% of antibody responses. Based on good experimental data, the RSVt vaccine was granted Fast Track Design and PRIME certification by the US Food and Drug Administration (FDA) and the European Medicines Agency (EMA) in December 2020 and December 2023, respectively. The approved global Phase III clinical trial (VAD00004) is a randomized, observer blinded, placebo-controlled, multicenter, and multinational study to evaluate the efficacy, immunogenicity, and safety of RSVt vaccines in infants and young children. The research subjects are infants and young children under 6 to 22 months old, without considering the RSV basal serum antibody status. The subjects will be randomly assigned two doses of vaccine or placebo in a 1:1 ratio, with a 56 day interval between the two doses, administered intranasally. This study does not include infants with weakened immunity, and the effectiveness of the vaccine on lower respiratory tract disease (LRTD) and upper respiratory tract disease (URTD) will be evaluated separately. Sanofi is committed to becoming a global leader in the field of immunology, and syncytial virus is one of the company's key areas of focus in the field of immune prevention. Synaptic virus is a common and highly contagious respiratory virus, with high-risk populations mainly concentrated in children, the elderly, and those with low immune function, resulting in a severe disease burden. To meet the differentiated prevention needs of different groups, Sanofi has laid out three products/R&D pipelines for the prevention of syncytial viruses, covering key populations such as infants, young children, and the elderly:? In December 2023, long-acting monoclonal antibody Le Weichu? The Nisetumab injection has been approved in China for the prevention of lower respiratory tract infections (LRTI) caused by respiratory syncytial virus (RSV) in newborns and infants. This is also the first respiratory syncytial virus prevention measure for all infants in China, and the product is expected to be launched during the RSV infection season from 2024 to 2025. ? The RSVt (SP0125) attenuated live vaccine for infants and young children is currently under development, which is the world's first designed syncytial virus vaccine for the protection of infants and young children. Phase III clinical trials are currently underway worldwide, and China is about to join the research. ? Sanofi is actively exploring a combination vaccine to help elderly people avoid diseases caused by syncytial virus infection. (Lai Xin She)