Epidemiology of viral gastroenteritis in children and genetic diversity of rotavirus strains in Kolkata, West Bengal after introduction of rotavirus vaccine

Background: Despite global rotavirus vaccination efforts, rotavirus remains a leading cause of childhood deaths from acute gastroenteritis. Post-vaccination studies in India, particularly in eastern India, have been limited, despite high prevalence of rotavirus in this region prior to vaccine introduction. This study was conducted to assess the impact of rotavirus vaccine on the epidemiology of rotavirus and other enteric viruses, as well as the changes in the diversity of rotavirus strains among children (<= 5 years) with acute gastroenteritis. Methods: A total of 877 stool samples from children hospitalized with acute diarrhea during 2022-2023, were screened for enteric viruses using multiplex PCR. Rotavirus positive samples were genotyped by sequencing and phylogenetic analysis of VP4 and VP7 genes were done. Results and discussion: Out of 877 diarrheal cases, 47 % tested positive for at least one enteropathogenic virus. Rotavirus was most prevalent (25.9 %), followed by norovirus (11.4 %), adenovirus-F (10.6 %), and astrovirus (5.3 %). Among mixed infections, rotavirus and norovirus co-infections were the most common. Rotavirus infection was highest in children aged 12-24 months, while other enteric viruses were more common in the 6-24 month age group. Clinical severity was higher among rotavirus-infected patients compared to those infected with other enteric viruses. The G3P[8] genotype of rotavirus predominated, with notable increase in G2P[4] and the detection of rare strains like G3P[6] and G11P[25]. G3P[6] was identified for the first time in this region showing Wa-like genome constellation. Unlike pre-vaccine period, G9 genotype was not detected. Mutations in antigenic epitope of circulating strains compared to vaccine strains may affect vaccine efficacy. Conclusion: The study highlights the persistent burden of childhood diarrhea despite rotavirus vaccination. Subtle alterations in the proportion of other enteric viruses and diversity of circulating rotavirus genotypes in the postvaccination period were observed. Continuous long-term surveillance is required to evaluate the impact of vaccine in this region.