Molecular epidemiology of human Respiratory Syncytial virus in Viet Nam National Children's Hospital

Respiratory syncytial virus (RSV) is a primary cause of pediatric severe acute respiratory infection (SARI) worldwide, especially in children under 2 years old. The burden of RSV infection was estimated as the second effect among respiratory diseases. However, the information on surveillance and molecular characteristics of RSV in Viet Nam is limited. From January 2017 to December 2020, 967 clinical specimens were collected from SARI patients at Viet Nam National Children's Hospital. All samples were screened and subtype by real-time RT-PCR. Selected positive samples with Ct under 25 underwent sequencing analysis targeting the G gene using next-generation sequencing. Data were analyzed with bioinformatic software and built phylogenetic trees. The RSV positivity rate was 33.3% (322/967 of samples), and prevalence was highest in children aged <1 year (52.8%; 170/322). Subtype RSV-A accounted for 53.42% (172/322) of cases, RSV-B for 45.96% (148/322), and two coinfection in 0.62% (2/322). Both subtypes cocirculated and peaked during August-September each year of research. Phylogenetic analysis showed that RSV -A samples belonged to the ON1 genotype with four lineages: lineage 1–4. However, the 72 nucleotide duplication in the second hypervariable region of the G gene, a characteristic of genotype ON1, was not found in any RSV-A sequences. RSV-B samples belonged to genotype BA9 with three lineages: lineage 1–3. P-distance among research lineages and other sequences in the same genotype was around 0.02-0.03. Our results are not only the updated information on circulation and molecular characterizations of RSV infections in Viet Nam but may also contribute to the growth of RSV vaccine development.