Rotavirus Vaccine Breakthrough With Vaccine‐Modified Disease in a Sibling Cluster of Equine‐Like G3P[8] Infection

ABSTRACT Rotavirus remains one of the major causes of childhood gastroenteritis despite the widespread introduction of rotavirus vaccines. Here, we report a sibling cluster of three children hospitalized with fever, vomiting, and diarrhea. Two unvaccinated siblings (11 years 9 months and 10 years 1 month) developed severe gastroenteritis with profuse watery diarrhea and prolonged hospitalization, while the youngest sibling (3 years 4 months), fully vaccinated with the RotaTeq vaccine, developed milder symptoms and had a shorter duration of hospitalization. Disease severity assessed using the modified Vesikari score indicated severe disease in the unvaccinated siblings (scores 16 and 11) and moderate disease in the vaccinated child (score 10). Rapid antigen testing followed by molecular analysis confirmed equine‐like G3P[8] rotavirus infections in all three patients. Epitope analysis of the VP7 protein identified four nonsynonymous substitutions (T87S, N213T, K238D, and D242A) within antigenic regions compared with the RotaTeq G3 vaccine strain. The reduced disease severity in the vaccinated sibling suggests partial protection conferred by the RotaTeq vaccine despite breakthrough infection and highlights the importance of continued molecular surveillance of circulating rotavirus strains.