Thanks Gary I emailed them and they did not even respond. At this point I will just do the yearly booster since I never did it. The Titers are pretty expensive at my vet but If I do get into competitive training for Obedience at the club I will inquire about titers or health certificates. There's no scientific evidence that boosters do anything for the dog's inmune system. I know Pharma companies want to make money and so do the vets.