Most vaccines require two injections. The first vaccine is considered the “priming dose” and the second injection is the “challenge” dose. The priming dose preps the immune cells to recognize the offending virus or bacteria and the challenge dose increases the amount of circulating antibodies, so the body can respond quickly if there is an infection.
But the rabies vaccine, by law, only requires one vaccination after 12 weeks of age in the puppy and kitten. The vaccine doesn’t work any different and by 70 days after that first vaccination, there is no sign of circulating antibodies at all! So why don’t we have to give a booster vaccine? Because if the puppy or kitten gets bit by a rabid animal, that becomes the “challenge” dose! It takes a long time for the rabies virus to get to the brain, so there is plenty of time for those dormant immune cells to recognize the virus and mount a good immune response.
But that first vaccine does require a more mature immune system and no interference from maternal antibodies. So we recommend giving that first rabies vaccine at 16 weeks of age, rather than at 12 weeks. If you have other questions about rabies, check out RabiesAware.org!
