Each year in the United States, norovirus causes between 19-21 million cases of acute gastroenteritis (about 1 in every 15 individuals will get norovirus illness annually); 1.7???1.9 million outpatient visits and 400,000 emergency department visits, primarily in young children; and about 56,000???71,000 hospitalizations and 570-800 deaths, mostly among young children and the elderly.