Flavivirus host-range mutations and uses thereof

A modified flavivirus envelope protein (E) comprising a mutated E protein N-terminal transmembrane domain (E-T1 domain), such a mutation comprising a proline substituted for one or more amino acids at position 0, −1, −2, −3, −4, −6, −8, +2, +3, +4, +5, or +6 (wherein the central amino acid of the E-T1 domain is numbered position 0, amino acids proceeding toward the N terminus are numbered −1, −2, etc., and amino acids proceeding toward the C-terminus are numbered +1, +2, etc.), wherein the effective membrane-spanning distance of the mutated E-T1 domain is shorter than the effective membrane-spanning distance of a wild-type E-T1 domain, and a virus comprising the modified flavivirus E protein has an ability to infect mammalian cells but a reduced ability to replicate therein relative to wild-type virus.