Background. The oral infant rotavirus vaccine, Rotarix, was introduced in England and Wales in July 2013. We estimated the impact on laboratory-confirmed rotavirus infections and hospitalizations for all-cause acute gastroenteritis (AGE) during the first year after introduction. Methods. We extracted data on laboratory-confirmed rotavirus infections (July 2000 through June 2015) and all-cause AGE-associated hospitalizations (July 2007 through June 2014) for all age groups using national databases (LabBase2 and HES). We determined the ratio of the rate during the 2013-2014 rotavirus season to the rate during the prevaccination era. Results. In infants, there was a 77% decline (rate ratio [RR], 0.23; 95% confidence interval [CI],. 16-.32) in laboratory-confirmed rotavirus infections and a 26% decline (RR, 0.74; 95% CI,. 65-.84) in all-cause AGE-associated hospitalizations in 2013-2014, compared with the prevaccination era. Large reductions were also observed in older children, adults, and older adults. We estimated that 10 884 laboratory-confirmed infections and 50 427 all-cause AGE-associated hospital admissions were averted in 2013-2014. Similar reductions have been observed for laboratory-confirmed rotavirus infections during the 2014-2015 season. Conclusions. The rapid declines in rotavirus infection and AGE in vaccinated and unvaccinated age groups within 1 year of introducing an infant rotavirus vaccination program are far greater than expected and than previously reported by other countries.