Abstract
During 1999β2000, a sustained mumps outbreak in the highly vaccinated population in Singapore was attributed to vaccine failure associated with the Rubini vaccine strain. To explain this phenomenon, the complete nucleotide and amino acid sequences of the hemagglutininβneuraminidase (HN) gene of eight mumps virus isolates from patients with parotitis in Singapore were determined and compared with those of known vaccine strains. Phylogenetic trees constructed on the basis of HN nucleotide and amino acid sequences showed that the Singapore mumps virus isolates were more closely related to the Urabe strain and belonged to a different cluster from the Rubini and JerylβLynn strains. The Rubini vaccine showed only βΌ93% nucleotide and βΌ96% amino acid sequence similarity to Urabe and Singapore isolates. Compared with the vaccine strains, six of the eight isolates lacked the extracellular glycosylation site at residues 400β402. Other significant amino acid disparities (e.g., at residue 354) may also affect the antigenic properties of the HN protein. These findings suggest that the evolution and adaptation of the currently circulating mumps virus strains in the community has led to the emergence of genetically distinct viral strains. The low vaccine efficacy of the Rubini strain represents a major reason for the recent mumps resurgence and failure of mumps immunization in Singapore. J. Med. Virol. 70: 287β292, 2003. Β© 2003 WileyβLiss, Inc.