Recombination between alphaherpesviruses has been commonly seen in vitro and has also been seen in vivo under experimental conditions. While this capacity for recombination has raised concerns about the use of attenuated alphaherpesvirus vaccines in human and veterinary medicine, to date these concerns have remained theoretical and the risk of recombination has been considered to be small due to the low probability of coinfection of the same cell under natural conditions. Here we show that independent recombination events between attenuated vaccine strains of infectious laryngotracheitis virus led to the generation of two distinct virulent recombinant viruses that became the dominant strains responsible for disease in major Australian poultry production areas. Our findings highlight the risks of using multiple attenuated herpesvirus vaccines with distinct origins in mass vaccination programs.