Modified live virus (MLV) vaccines have been effective in reducing disease burden and economic loss caused by Newcastle Disease (ND) in domestic poultry. Because the vaccine is a live virus, it is transmissible among birds. Thus, vaccination strategies have the potential to impact the evolutionary genetics of wild type strains of aPMV-1 including those that cause ND. In this report, we provided evidence that viruses isolated from wild and domestic birds have recombined with vaccine strains, because vaccinated birds are protected from disease but not infection with other strains of aPMV-1. Despite the use of vaccines since the 1950s, the population size of the strain from which the most widely used vaccine was derived has steadily increased. In contrast, other contemporary genotypes, which emerged in the 1960s, experienced a decline in population size in 1998, which may reflect a change in poultry farming practices or disease. Vaccination imposed a unique selection profile on the genotypes derived from the vaccine-related strains when compared with nonvaccine-related strains. Although modified live viruses are important for controlling Newcastle Disease, the potential of vaccination strategies to change viral diversity and population dynamics should be considered. and is not present in our sequences. However, the RDP3 program reasonably identified the 59 breakpoint at the 8th nucleotide of the F-gene. Two additional recombination breakpoints within this insert were also detected by the GENECONV and Bootscan methods (p-value 2.29610 23 and 3.35610 22 ). These corresponded to the positions in the F gene segment of KBNP-4152 strain that were mutagenized to attenuate recombinant strain EU140955. Thus, we conclude that the RDP3 program accurately identifies recombination if five or more methods have statistical support of p#10 25 for the breakpoints and we propose that any breakpoints statistically supported with only one or two methods should be carefully interpreted.