Use of both modified-live vaccines and killed vaccines are contraindicated for immunization of pregnant bitches unless the vaccine has been specifically approved for this purpose or risk of contracting an infectious disease exceeds potential risks of vaccinating to the dam and litter. Problems associated with vaccination during pregnancy include fetal resorptions, spontaneous abortions, and birth defects. Advanced proper planning prior to the bitch's breeding cycle, which would include updating necessary inoculations, should exclude the necessity to vaccinate during pregnancy. Routine annual booster administration does not justify risks and should be postponed until the litter is whelped and the puppies are weaned