Characteristics of Rotavirus Infections before and after Introduction of Rotavirus Vaccines in Japan

Rotavirus infection is a serious gastrointestinal infection that is usually prevalent during winter months and often seen in infants and young children. Studies on genotypes of prevalent rotavirus strains are quite important for preventing infection, developing vaccines, and its evaluation. We investigated the characteristics of rotavirus infections of Nasu Region of Tochigi, Japan and to compare to the other region before introduction of rotavirus vaccines. We examined the clinical findings in 147 patients and analyzed the clinical findings of the 37 patients with a fecal sample positive for rotavirus antigen. Furthermore, viral genotypes were determined using rotavirus-positive samples from 27 of these 37 patients. The genotypes were determined as G1P [8] in 5 samples, G3P [8] in 5 samples, G9P [8] in 3 samples, and G6P [9] in 2 samples. We were able to analyze the phylogenetic trees of these genotypes. Of particular note, we detected G6P [9] which were extremely rare in human beings but common in cattle. It was suggested that the rates of hospitalization due to rotavirus infections of infants from 6 to 11 months of age would be reduced by 42% when the vaccination coverage rates increase to 50% in Japan. Studies on changes in prevalent strains after vaccine introduction need to be conducted.