Flewett's work on rotaviruses brought him international recognition both as a virologist and an electron microscopist. He was one of the first western virologists to be invited to the People's Republic of China (in 1983) to lecture. He was a judge for the King Faisal International Prize in 1983, which was awarded to Professor John S. Fordtran, Dr William B. Greenough III and Professor Michael Field, for their work on oral rehydration therapy in reducing mortality and morbidity due to cholera and other acute infectious diarrhoeal diseases.