Effects of the in ovo injection of Inovocox EM1 vaccine (EM1 vaccine) suspended in commercial diluent on developing broiler embryos were investigated in 3 trials. Effects of the EM1vaccine administered by in ovo injection on broiler embryogenesis and posthatch performance was determined by evaluating site of injection (SOI), embryo staging (ES), hatchability, and chick quality parameters. Oocyst output, microscopic lesion scores, and grow-out performance were further examined through day 35 posthatch. In these studies, it was shown that oocyst output began at day 3 posthatch (6 days post-injection), and peaked at day 7 posthatch (10 days post-injection). The EM1 vaccine had no effects on hatchability, various and chick quality parameters that were examined in the study. Similarly, grow-out performance through day 35 posthatch was not affected by the EM1 vaccine. SOI and ES provided information on the accuracy of in ovo vaccine delivery to the embryos, and were found to be significantly influenced by embryo age. In conclusion, in ovo injection of the EM1 vaccine has no detrimental effect on broiler embryogenesis, hatching chick quality, or the performance characteristics of Ross × Ross 708 broilers.