Phylogenetic relationship of vaccine strains R2B and strain F (boxed) based on Fusion protein gene.

<p>The phylogenetic tree was drawn using maximum likelihood method employed in MEGA program (Version 5). The percentage of replicate trees in which associate taxa clustered together in the bootstrap test (1000 replicates) is shown next to the branches. Trees are drawn to scale, with branch length in the same units as those of the evolutionary distances used to infer the phylogenetic tree. The evolutionary distances were computed and are in the units of the number of base substitutions per site.