Choosing and using vaccines in the animal shelter

The principles involved in designing a vaccination program for the animal shelter are the same general principles behind any disease prevention program. The difference is in the relative importance of various concepts as they pertain to the shelter population and environment. Shelters take animals from a wide variety of sources, occasionally with a detailed medical history but most often with little or no information. The risk of exposure to infectious disease is much higher in the shelter than for the general population, and the subclinically infected or mildly afflicted animals pose the greatest danger, especially to the young.

Shelter animals require a diffeent approach when it comes to vaccination. If possible, it is best to try to get a complete record of the animal's history from the adopting shelter.

The principles for vaccination

It is useful to divide vaccines into "core" and "non-core," where the latter are optional depending on the animal's home environment and "lifestyle," e.g. hunting dog vs. lap dog. In most shelters, the "non-core" concept is not relevant. Core vaccines protect against highly contagious, often endemic diseases with significant mortality, morbidity or economic consequences. The core of a shelter vaccination program is likely to differ from one in private practice and among shelters. Shelter protocols may vary according to differences in location, facilities, resources, average length of stay, and mission or philosophy, e.g. limited admission vs. animal control. If vaccination for Microsporum canis effectively and economically prevented dermatophytosis, for example, it might be routine in many shelters, but few practices.

In any case, risk and efficacy have to be weighed against expense. Shelters often have small budgets and no hope of recouping costs from adopters. Some shelters use the intranasal vaccine against Bordetella in cats, but the cost per dose puts a premium on determining the significance of the disease in that particular environment. Whereas having many animals from many places in close proximity argues for a comprehensive vaccination program, economics is often a limiting factor. Another problem is the lag between vaccine administration and, if all goes well, immunization. Waiting or quarantine periods are advisable if not always feasible. Injectable vaccines may take over a week to induce immunity.

For legal and public health reasons, vaccination against rabies is warranted before (or shortly after) adoption, even though rabies exposure is highly unlikely in the shelter. It should arguably not be done until any waiting period for lost animals is past or until ownership is signed over to the shelter, or when there is proof of current vaccination. An animal suspected or known to have bitten someone cannot be vaccinated and requires close observation or testing. Animals with suspicious bite wounds pose a dilemma. If previously vaccinated, they would be boostered; if not, vaccination will not protect them but may slow the onset of the disease. Realistically, unknown animals with severe unexplained bite wounds are probably too great a risk and require too much time and expense for a shelter to handle.

Table 1: Proposed Categorization of Infectious Diseases/ Vaccines for Animal Shelter Protocols

Providing protection

Protection against canine and feline parvovirus (panleukopenia) is essential. Young animals are exposed to virus in the environment, where it is very difficult to inactivate. Kittens and puppies should be vaccinated as early as 6 weeks of age, then every two to three weeks until the age of 3 months in kittens and 4 months in pups. If we start at 6 or 7 weeks of age, I give the first booster two weeks later. High-titer low-passage canine parvovirus vaccines should be used, and highly susceptible breeds should be given boosters until they are more than 5 months of age. The protocol for canine distemper and adenovirus vaccination follows that for parvovirus. If canine distemper is a known threat, the distemper/measles vaccine can be used in pups at 6 weeks of age. It should be given in the muscle. Adults, even with no vaccine history, do not need a three to four week booster for these viruses.

Whether or not to include Leptospira in dog or puppy vaccines depends on the incidence of leptospirosis in the area, public perceptions and concerns, the presence (or absence) of relevant serovars in the vaccine, and the possibility of adverse reactions and a short duration of immunity. If used, adult dogs need a booster shot in three to four weeks. The significance of canine coronavirus as a cause of clinical disease in shelters is unknown. It might be relevant in some multiple-dog environments, where vaccination is recommended every six months, but it seems to cause only mild disease in young pups under certain conditions.

Intranasal vaccination against Bordetella bronchiseptica and canine parainfluenza virus in dogs is routine in a multiple-dog setting, and can be given to 4-week-old pups. It does not protect against all causes of infectious tracheobronchitis, and should be repeated at six-month intervals as long as there is a risk of exposure. In cats, more relevant than the intranasal feline Bordetella vaccine is the topical bivalent vaccine against calicivirus and herpesvirus (rhinotracheitis), which is administered in the eyes and nares. There is no advantage to including panleukopenia in the vaccine, and it has been implicated in an outbreak of salmonellosis in kittens.

Routine in some shelters, but not others, topical vaccination against feline respiratory viruses should induce immunity in as little as two to three days at the sites of viral attack. More data is needed on the efficacy of the vaccine in shelters, but one study showed a significant decrease in the occurrence and severity of upper respiratory infection (URI). My sense is that the incidence of URI is roughly the same since we started using the vaccine at the American Society for the Prevention of Cruelty to Animals (ASPCA) two years ago, but there are fewer severe cases among vaccinates. For example, we have seen fewer cats with caliciviral lingual ulceration. The apparent disease incidence may include many vaccine reactions, which can occur days after inoculation and resemble mild URI.

Vaccination of cats against Chlamydia or FIP, even where there are significant problems, is probably not cost-effective in the shelter, partly due to questionable efficacy. The risk of exposure to feline leukemia virus in cats and Lyme borreliosis in dogs depends on setting and lifestyle. Whether or not to vaccinate against them is probably best left to the discretion of the owners and their veterinarians after adoption. Ideally, all cats are tested for feline leukemia virus and feline immunodeficiency virus before adoption if resources allow.

Decision process

It is important for veterinarians in private practice to understand that a decision to give a sheltered animal one vaccine and not another is based on medical, financial and practical considerations in the shelter. In some cases, for example adult animals in a shelter with a "lost and found" function and a high turnover, vaccines are withheld. It would be wrong to imply neglect on the part of the shelter for not giving a vaccine that is considered "core" in a particular practice area. It is also worth noting that when and how vaccines are used is legally at the discretion of the veterinarian. Regulations concerning extra-label use do not apply. We must consider the principles of immunology and what we know about particular diseases and vaccines, as well as the best interests of the individual and the population we are trying to protect.