Rotavirus Genotype Dynamics and the Emergence of G3P[8] in Thailand Following Nationwide Vaccine Implementation

Rotavirus A is a leading cause of acute gastroenteritis in infants and young children under the age of five worldwide. The introduction of two live-attenuated oral vaccines, Rotarix and RotaTeq, has significantly decreased illness and death associated with rotavirus in countries where they are included in childhood immunization schedules. In Thailand, these two vaccines have been part of the national childhood immunization program since 2020. To monitor the changing patterns of rotavirus genotype distribution in the post-vaccination era, a molecular epidemiological study of rotavirus A was conducted in pediatric patients with acute diarrhea in Chiang Mai from 2020 to 2023, which was the period after the rotavirus vaccine was implemented in Thailand. A total of 1192 stool specimens collected from children with acute gastroenteritis were screened for rotavirus A by real-time PCR. The G- and P-genotypes were determined by using semi-nested PCR and nucleotide sequencing. A total of 60 out of 1192 (5.0%) samples were positive for rotavirus A. Among these, G3P[8] (55.0%) was identified as the most prevalent genotype, followed by G8P[8] (15.0%), G1P[8] (13.2%), G9P[8] (3.3%), G2P[4] (3.3%), G1P[6] (1.7%), G9P[4] (1.7%), and G8P[X] (1.7%). Additionally, the unusual rotavirus strains G3P[9] (1.7%), G3P[23] (1.7%), and G5P[23] (1.7%) were detected in this study. Phylogenetic analysis of the VP7 and VP4 genes revealed that the G3P[9] strain was closely related to those of feline rotaviruses, while the G3P[23] and G5P[23] strains showed high similarity to those of the porcine rotavirus strains detected previously in Thailand. This study demonstrated a significant decline in the prevalence of rotavirus A infection in pediatric patients in Chiang Mai, Thailand, during the post-vaccination period. The findings from this study contribute to a better understanding of rotavirus epidemiology in Thailand following the implementation of the rotavirus vaccines.