Overdue Vaccination

1. How many doses of vaccine should be given to a dog presented for their initial vaccine series if the patient is older than 16 weeks of age?

Two sequential doses, administered 2 to 4 wk apart, are conventionally recommended. Doing so is essential when initially administering a killed (inactivated) vaccine. Rabies is the exception to this rule (see the FAQs on RABIES).

Among dogs 16 wk of age and older, administration of a single dose of a core vaccine is likely to immunize. However, given that a small number of dogs at 16 wks of age may still have interfering levels of maternally derived antibody, administering 2 doses, 2 to 4 wk apart, is a reasonable recommendation.

2. When administering the initial doses of a killed (inactivated) vaccine that requires 2 doses to immunize (e.g., leptospirosis, Lyme disease, CIV), and the dog does not return for the second dose within 6 weeks after the first dose, does the 2-dose “series” need to be restarted?

Killed (inactivated) vaccines require 2 doses on initial vaccination. The first dose primes the immune system, and the second dose immunizes. While it is ideal to have the second vaccination given within 4 wk, the Task Force considers 6 wk to be the “outside limit” between initial vaccinations, beyond which the series would need to begin again (two additional doses, administered 2 to 4 wk apart).

Rabies vaccine is the exception. In states, jurisdictions, and provinces (Ontario) that require rabies vaccination of dogs, administration of a single dose of rabies vaccine, regardless of the time that has elapsed since the previous dose was administered, is considered to be an immunizing dose. Following revaccination, a dog is considered to be immediately “currently vaccinated” against rabies. See the FAQs within the section on RABIES.