Human respiratory syncytial virus: pathogenesis, immune responses, and current vaccine approaches.

Respiratory syncytial virus continues to pose a serious threat to the pediatric populations worldwide. With a genomic makeup of 15,200 nucleotides, the virus encodes for 11 proteins serving as envelope spikes, inner envelope proteins, and non-structural and ribonucleocapsid complexes. The fusion (F) and attachment (G) surface glycoproteins are the key targets for neutralizing antibodies. The highly variable G with altered glycosylations and the conformational alternations of F create challenges for vaccine development. The metastable F protein is responsible for RSV-host cell fusion and thus infectivity. Novel antigenic sites were identified on this form following its stabilization and solving its crystal structure. Importantly, site ø displays neutralizing activity exceeding those of post-F-specific and shared antigenic sites, such as site II which is the target for Palivizumab therapeutic antibody. Induction of high neutralizing antibody responses by pre-F immunization in animal models promoted it as a major vaccine candidate. Since RSV infection is more serious at age extremities and in individuals with undermining health conditions, vaccines are being developed to target these populations. Infants below three months of age have a suppressive immune system, making vaccines' immunogenicity weak. Therefore, a suggested strategy to protect newborns from RSV infection would be through passive immunity of maternal antibodies. Hence, pregnant women at their third trimester have been selected as an ideal target for vaccination with RSV pre-F vaccine. This review summarizes the different modes of RSV pathogenesis and host's immune response to the infection, and illustrates on the latest updates of vaccine development and vaccination approaches.