Rabies vaccinations: titers, exemptions, and protocols
- Why is a single, initial dose of killed (inactivated) rabies vaccine able to immunize a dog, whereas 2 doses (2 to 4 wk apart) are required for all other killed vaccines?
All canine rabies vaccines licensed in the United States and Canada are inactivated (killed) vaccines. Conventionally, 2 sequential doses of an inactivated vaccine, administered 2 to 4 wk apart, are required to immunize (e.g., leptospirosis, Lyme disease, canine influenza virus).
Rabies virus vaccine is an exception. Like other inactivated vaccines, the initial dose of a rabies vaccine serves as the “priming” dose. If a dog, after having received only 1 dose of rabies vaccine, is subsequently exposed to virulent rabies virus, exposure to the virulent virus then serves as the second, or immunizing, “dose.” Because the onset of signs of rabies is slow (weeks to months) following exposure there is adequate time for a protective, humoral immune response to develop. For this reason, rabies infection in vaccinated dogs/cats, even among those having received a single dose, is exceptionally rare.
Exemptions to rabies vaccination
- In locations that require dogs to be vaccinated against rabies, can a licensed veterinarian exempt the requirement to administer a rabies vaccine if the patient is sick or there is a risk that doing so may result in an adverse reaction or otherwise cause injury to the patient?
Point-of-care exemptions of the rabies vaccination requirement are NOT authorized in most states (for information on your state see: www.rabiesaware.org).
Within states and jurisdictions that require rabies vaccination of dogs, unless rabies vaccination exemption authority is specifically defined by state statute or regulation, rabies vaccine must be administered at the appropriate interval regardless of the dog’s age or state of health.
Currently a small number of states do grant point-of-care rabies vaccination exemption authority to veterinarians. Some states/jurisdictions allow exemptions but only with the approval of a designated Public Health official (usually a veterinarian). Exemptions may be allowed in the event an individual dog is determined to be sufﬁciently ill or if rabies vaccination poses a potential threat to life. Physical examination and medical record documentation of the illness is likely to be required; it is the responsibility of the owner and the veterinarian to ensure the dog is revaccinated when or if the underlying medical condition resolves.
NOTE: Among cases in which a rabies vaccination exemption has been approved and is in effect, the “exempted” dog/cat will not be considered “currently vaccinated” (immunized) if the rabies booster interval (i.e., either 1 yr or 3 yr) has been exceeded.
Due to the potential implications associated with rabies exposure in a dog that is not “currently vaccinated” against rabies, the owner should be involved in the decision-making process of whether or not to vaccinate, and the veterinarian should document the discussion in the patient’s medical record.
Veterinarians practicing in locations where rabies vaccination is required, but exemption authority is not speciﬁcally deﬁned, should contact the state (State Public Health Veterinarian) or provincial Department of Health (Ontario) for guidance on this issue before vaccinating a dog with a medical condition that, in the veterinarian’s judgment, precludes administration of rabies vaccine.
Overdue for rabies booster
- If a healthy dog is overdue for a rabies booster (and has documentation of prior vaccination), what is the appropriate protocol for revaccination?
In a majority of the states and jurisdictions that require rabies vaccination of dogs, administration of a single dose of rabies vaccine, regardless of the time that has lapsed since the previous dose was administered, is considered to be an immunizing dose.
In most states, following revaccination, a dog is considered to be immediately “currently vaccinated” against rabies. In most states, the duration of immunity of the booster dose is determined by the product label (i.e., either 1 yr or 3 yr).
Some states do require all dogs that are overdue for revaccination, even if by just one day, to receive 2 rabies vaccine doses 1 yr apart. (For your state, see www.rabiesaware.org).
- Does a “positive” rabies antibody test result correlate with protective immunity?
No. At least not in a legal sense. IMPORTANT: In the United States and Canada, a “positive” test result for rabies virus neutralizing antibody (RVNA) is not recognized as an index of protective immunity and cannot be used in lieu of revaccination.
As of 2017, RVNA (regardless of the methodology used), denotes prior vaccination only and is predominantly limited to use in dog/cats being exported from the United States/Canada to rabies-free countries/regions of the world. Testing is a requirement imposed by the importing country/region as a means of confirming recent vaccination against rabies and is not regarded as evidence of protective immunity against rabies.
- After receiving a single, initial dose of rabies vaccine, will a dog have a “positive” fluorescent antibody virus neutralization (FAVN) test result for a full year?
Not likely. The antibody test result (FAVN) performed in dogs that have received a single, initial dose of rabies vaccine can be expected to manifest a “positive” test result for a limited time (up to about 3 months) post-vaccination. Age of the dog, giant breeds versus smaller breeds, and individual patient response to vaccine antigen influence the amplitude and duration of serologic response following a single dose of rabies vaccine.
Dogs undergoing FAVN testing prior to exportation are more likely to have a negative (“failing”) test result if they have received a single dose of vaccine versus 2 or more doses.