Live attenuated metapneumovirus strains and their use in vaccine formulations and chimeric metapneumovirus strains

An isolated mammalian metapneumovirus, wherein the isolated mammalian metapneumovirus comprises a genetic modification at one or more of the nucleotide positions selected from the group consisting of:

• position 197 in the P open reading frame;
• position 9, 113, 155, 336, 394, and 436 in the M open reading frame;
• positions 277, 301, 325, 839, 1412, 1594, and 1612 in the F open reading frame;
• position 560 in the M2 open reading frame;
• position 415 and 491 in the G open reading frame;
• and positions 703, 967, and 4357 in the L open reading frame.

An isolated mammalian metapneumovirus, wherein the isolated mammalian metapneumovirus comprises a genetic modification resulting in one or more amino acid changes selected from the group consisting of:

• position 66 in the P protein is altered to Val;
• position 9 in the M protein is altered to His;
• position 38 in the M protein is altered to Ser;
• position 52 in the M protein is altered to Pro;
• position 132 in the M protein is altered to Pro;
• position 93 in the F protein is altered to Lys;
• position 109 in the F protein is altered to Ser;
• position 280 in the F protein is altered to Gly;
• position 471 in the F protein is altered to Arg;
• position 532 in the F protein is altered to Tyr;
• position 538 in the F protein is altered to Tyr;
• position 187 in the M2 protein is altered to Ile;
• position 139 in the G protein is altered to Pro;
• position 164 in the G protein is altered to Pro;
• position 235 in the L protein is altered to Arg;
• position 323 in the L protein is altered to Asp;
• and
• position 1453 in the L protein is altered to Leu.