In the event a pet owner does not, or is not able to, adhere to the conventional vaccination schedules outlined, the following recommendations provide reasonable, alternative schedules that offer the most appropriate vaccines at the most appropriate intervals.
Overdue During Initial Vaccination Series
For the juvenile (< 16 weeks of age) dog and cat, the initial vaccination series with core vaccines is critical.
During this series, a dog or cat can be considered overdue for vaccination if the patient is not returned within 6 weeks following administration of the previous dose. However, there are no published studies defining the specific intervals between initial doses of vaccine required to assure a protective immune response.
It is reasonable to recommend an alternative vaccination schedule for a dog or cat determined to be overdue. Deciding which vaccine should be administered and when is based on 2 factors:
Elapsed time since the previous dose
Type of vaccine (recombinant, attenuated, or inactivated) being recommended.
Attenuated Vaccines + Recombinant CDV Vaccine
If protocol involves administration of an attenuated vaccine (or the recombinant CDV vaccine), a single dose is expected to immunize, if administered in the absence of maternally derived antibody (MDA).
The challenge is determining when MDA levels no longer interfere with immunization in the individual patient. In most dogs and cats, MDA is expected to decline to noninterfering levels by 16 weeks of age. Common scenarios include:
A puppy receives a single (combined) dose of core vaccines at 7 weeks of age; however, the puppy isn’t returned for the second dose until 9 weeks later, at 16 weeks of age.
Administration of a single dose of a recombinant or attenuated vaccine is expected to immunize.
Alternatively, administration of 2 additional doses, 2 to 6 weeks apart, rather than 1, would also be considered appropriate.
A dog or cat older than 16 weeks of age is presented to the practice for the first time.
Surveys of veterinarians practicing in the U.S. and Canada indicate that 2 doses, 2 to 6 weeks apart, are conventionally recommended.
Inactivated Vaccines + Recombinant Noncore Vaccines
When administering inactivated vaccines or recombinant noncore vaccines (eg, leptospirosis, Lyme borreliosis, FeLV), 2 initial doses are required to induce protective immunity, regardless of patient’s age at time the first dose is administered.
The primary immune response following administration of the first dose of an inactivated vaccine (or recombinant FeLV or Lyme borreliosis vaccine) is relatively weak and short-lived (sometimes referred to as priming).
A patient that receives only a single dose of inactivated vaccine is unlikely to develop a sustained protective immune response.
Rabies vaccination is the obvious exception.
The secondary immune response following administration of the second (immunizing) vaccine dose is relatively robust and has rapid onset (anamnestic).
This protective immune response is sustained for months or years.3-5
Protective immunity is expected to develop by 7 days following administration of the second dose of an inactivated vaccine.
The interval between the first (priming) and second (immunizing) doses of an inactivated vaccine is important: If the interval between the initial 2 doses is inordinately prolonged, the anamnestic response to the second dose may be significantly diminished, leaving the patient susceptible if exposed.
During the initial series, using a noncore vaccine, any patient with a vaccination interval that exceeds 6 weeks between doses should receive 2 additional doses, 2 to 6 weeks apart. Common examples include:
A kitten receiving the first dose of an FeLV vaccine at 10 weeks of age that returns 2 months later for the second dose.
A dog presenting for its first dose of Lyme borreliosis vaccine (inactivated or recombinant) at 3 years of age that returns 3 months later for the second dose.
See Tables 2 and 3 for a summary of recommendations for puppies and kittens overdue for vaccination during initial (juvenile) series.
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