Changes in the Proportion of Gastrointestinal Emergency Endoscopy and Peptic Ulcer Disease During the COVID-19 Pandemic: A Local Retrospective Observational Study From Vietnam oleh Hang Viet Dao, Hang Viet Dao, Long Bao Hoang, Nha Ngoc Hoa Le, Trang Thi Thu Tran, Trang Thi Thu Tran, Hung Manh Nguyen, Long Van Dao, Long Van Dao, Ngoan Tran Le, Ngoan Tran Le