Beyond Rotavirus: Persistence of Norovirus, Adenovirus, and Astrovirus in Paediatric Gastroenteritis in the Republic of Congo After Vaccine Introduction.

Despite the introduction of rotavirus vaccines, gastroenteritis remains a major cause of paediatric morbidity and mortality in the Republic of Congo. This study investigated the prevalence and genetic diversity of non-rotavirus enteric viruses including norovirus (NoV), adenovirus (AdV), and astrovirus (AstV) ten years after the introduction of the rotavirus vaccine in 2014. A cross-sectional study was conducted between 2022 and 2023 among 227 children (≤ 5 years old) hospitalised for acute gastroenteritis in Brazzaville. Stool samples were analysed by multiplex RT-PCR to detect RVA, NoV, AdV, and AstV. Positive AdV and NoV samples underwent genotyping by PCR and sequencing. The incidence of gastroenteritis peaked during the dry season, with the highest burden observed among children aged 6-24 months. Overall, 75% (n = 170/227) of children tested positive for at least one virus; RVA was detected in 58% (n = 131/227), followed by NoV in 34% (n = 77/227), AdV in 11% (n = 24/227), and AstV in 7% (n = 16/227), while 25% (n = 57/227) tested negative for all four viruses. Co-infections were observed in 32% of children (n = 72/227), most commonly RVA-NoV. The predominant genotype of norovirus was GII.P31 (82%), and that of adenovirus was type 41 (67%). Notably, from November 2022, gastroenteritis of unknown aetiology peaked, coinciding with a decline in the four targeted viruses. NoV, AstV, and AdV continue to contribute to the gastroenteritis burden in Congolese children. The high circulation of NoV and the seasonal surge of unexplained cases highlight the need for broadened molecular surveillance, incorporation of bacterial diagnostics, and consideration of future NoV vaccine strategies.