Researcher have found a new sublineage of enterovirus A71 (EV-A71) C4 subgenotype with two possible recombinant strains during the 2015-16 outbreak of hand-foot-and-mouth disease in Hanoi, northern Vietnam. Further, they confirmed that the EV-A71-C4 subgenotype may be more virulent than the B5 clinically and experimentally with transgenic mouse model. This has helped elucidate the outbreak and may identify candidate viral strains for developing polyvalent vaccines.