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A Vaccination Education

Decoding the true risks and benefits of vaccines

While some have questioned the safety of vaccines, they remain a powerful tool for helping animal advocates protect pets against disease, both in and out of the shelter environment. Shutterstock

by Brenda Griffin, D.V.M.

Vaccines have long been a mainstay of routine preventive health care for both people and animals. Their use has controlled and prevented widespread epidemics of numerous infectious diseases that otherwise would claim many human and animal lives each year. In the past few years, however, the safety of vaccination has been called into question. Vaccines have been blamed for the development of many chronic diseases, including cancer. Such claims have led medical professionals to study not only the potential benefits of vaccination, but also the possible risks. In addition, panels of experts have convened to develop professional guidelines for vaccination in order to ensure that vaccines are used both effectively and judiciously to safely prevent disease.

Remember When?

In the 1970s, when canine parvovirus first emerged, no one knew the cause of this rapidly spreading and often deadly disease. If you were working in the animal care field back then, you probably have vivid memories of that scary time; even if you weren’t, you may recall the nightly television news stories, which made us all fear for the safety of our beloved dogs.

I was teenager at the time, and had an after-school job at a local veterinary clinic. We were quickly overwhelmed with severely ill dogs suffering from cases of a mysterious acute bloody diarrhea. Most of the dogs we saw died, despite our attempts to treat them, leaving distraught, grief-stricken owners, as well as a panicked community. Fortunately, veterinary researchers immediately began work to isolate the cause of the epidemic and then to develop a vaccine to prevent it.

I remember when the first canine parvovirus vaccines arrived at the clinic. Cars lined up outside, and the veterinarian administered the precious vaccines to dogs in the backseats of their owners’ cars before sending them on their way. As more and more dogs received the vaccine, we saw less and less disease in the community. There was no doubt this was a lifesaving tool.

My family was fortunate—our dogs were not infected with the deadly virus, but my best friend’s family was not so lucky. They lost their beloved Dalmatian, Drafty, and were devastated beyond words. I remember speaking to the veterinarian who ran the emergency clinic where Drafty was treated. It was a nightmare for him to deliver such horrible news to so many owners whose dogs had been young and healthy just days or hours before they succumbed to the deadly infection.

Times are A-Changin’ …

Thirty years later, the Internet is filled not only with success stories about vaccination, but with many warnings about its purported dangers. Countless testimonials and blogs claim that children and pets are healthier without vaccination, while heartbreaking news stories report the deaths of children and pets who have died from preventable diseases because they were not vaccinated. Passionate and convincing arguments stoke the often highly contentious debate over whether vaccines are vital, lifesaving tools, or dangerous, unnecessary, and overused drugs.

Opponents of vaccination often point fingers at the “greedy” drug companies and doctors that push these products. There is no doubt that drug companies strive to make money—of course they do—but they also invest millions of dollars in research and development to advance medicine and health care. I know I am grateful that they provided funding to develop canine parvovirus vaccines, and over the last three decades, they have continued to improve them. Meanwhile, the debate continues regarding the merits and risks of vaccination, leaving pet owners to sift through various well-intentioned recommendations to determine whether or not they will vaccinate their own pets, and if so, against what and how often.

Risks Vs. Benefits

The decision to vaccinate should always be made in the context of the potential risks and benefits to an individual patient. In animal shelters, the high likelihood of exposure and the potentially life-threatening consequences of illness make the decision to vaccinate very straightforward: There is absolutely no doubt that proper vaccination substantially reduces disease in shelters and improves animal health. Thus, the benefits of vaccination of cats and dogs in these environments far outweigh the potential risks for adverse side effects from the procedure.

The risk of disease exposure in susceptible animals is high whenever there are frequent introductions of new animals with an unknown health status, so foster homes and home-based rescue groups also represent a relatively “high risk” environment if they provide care for susceptible animals from different sources. In particular, young animals, especially those less than 6 months old, are often highly susceptible to infectious diseases. For homes that have housed sick animals, the risk may be even higher because—depending on the infectious agent in question—it may be difficult to sanitize the environment once contamination has occurred. This is because some viruses, including canine and feline parvovirus, have the ability to survive for months and are relatively resistant to cleaning and disinfection, especially when they are deposited on porous surfaces such as carpet, grass, or wood. Once contaminated, these surfaces may continue to harbor the viruses for a very long time, increasing the odds of exposure and illness when susceptible animals are introduced to such an environment.

Core Vaccines in Shelters and Foster Homes

Although many vaccines are commercially available for cats and dogs, only a few “core vaccines” are recommended for routine use in shelters and rescues and their associated foster homes. Core vaccines are those known to provide effective protection against important diseases that commonly cause significant illness in shelter animals.

For cats these include modified live feline parvovirus (FPV or panleukopenia); FHV-1 (feline herpes virus type 1 or feline rhinotracheitis virus); and feline calicivirus (FCV), administered in combination as an injectable FVRCP vaccine (feline viral rhinotracheitis, calicivirus, panleukopenia).

  • Kittens and puppies are the most susceptible to infectious diseases. A rule of thumb: Even if they are very little, if animals can eat and walk, they should be vaccinated immediately upon intake to a shelter. Shutterstock

For dogs, they include modified live canine parvovirus (CPV); canine distemper virus (CDV); and canine adenovirus (CAV-2, hepatitis), administered in combination as an injectable DHP vaccine (distemper, hepatitis, parvovirus).

In addition, intranasal Bordetella bronchiseptica + parainfluenza (CPiV) vaccine (commonly referred to as “kennel cough” vaccine) is also considered a core vaccine for shelter dogs.

For both dogs and cats, consideration should also be given to the provision of rabies vaccinations, not because the animals are highly likely to be exposed to the deadly virus in a shelter or foster home, but because of the implications for public health as well as the legal requirements imposed by many jurisdictions. Whenever possible, rabies vaccination should be performed prior to adoption, as well as any time animals are held long-term in shelter or foster facilities. Rabies vaccination may also be required by retail facilities that provide space to showcase adoptable animals.

Noncore Vaccines

On occasion, other vaccinations may be indicated for shelter animals because the diseases pose a known risk for a particular population. Such “noncore vaccines” include feline leukemia virus (FeLV), Chlamydophila, and Bordetella for cats, and canine influenza for dogs. Identifying FeLV-infected cats through testing and separating positive cats from those who test negative are very effective means of reducing the risk of exposure since transmission requires very close cat-to-cat contact. Because testing is not foolproof, vaccination against FeLV is recommended when cats are group-housed or housed long-term in shelter-like environments because of the associated increased risk of exposure.

Chlamydophila and Bordetella vaccines may be of moderate benefit when clinical signs of these diseases are present in the shelter and diagnosis is confirmed by laboratory testing. Similarly, canine influenza vaccination may be warranted when disease risk is documented. A veterinarian can determine if noncore vaccines are indicated in a given population and help to create a tailored protocol that will best facilitate disease control.

Unnecessary use of vaccines should always be avoided, both to minimize the incidence of adverse reactions and to reduce costs. Some vaccines are not generally recommended for use in shelters at all because they are unlikely to provide protection against disease. These include feline infectious peritonitis (FIP) for cats, and canine coronavirus, leptospirosis, and Borrelia burgdorferi (Lyme disease) for dogs.

Do They Really Work?

Although core vaccines can rapidly protect animals from many diseases in as little as a few days, they are not “magic bullets” that can prevent disease altogether. In some instances, they provide only partial protection, lessening the severity of clinical signs but not preventing infection. For example, canine and feline upper respiratory disease cannot be prevented by vaccination, but vaccination can still be of substantial benefit to minimize the frequency and severity of disease.

In contrast, timely vaccination against panleukopenia, canine parvovirus, and distemper virus usually prevents clinical disease altogether. That said, even the best vaccines take some time to provide protection, and vaccine failure may occur when animals enter the shelter already infected with disease, or if they fail to respond to the vaccine, or are exposed before they are able to do so. Finally, it is important to realize that vaccines are not available for every infectious disease that an animal might encounter.

Timing is Everything

Timing of vaccinations can make all the difference in their effectiveness in shelter and rescue settings. In these environments, it is literally a race between developing immunity from vaccination and developing the disease from exposure to infectious agents.

  • For kittens and puppies, vaccines should be administered every two weeks until they are approximately 5 months old. A kitten can be assumed to be approximately 5 months old by
    the time she weighs 4-5 pounds. Shutterstock

In an ideal world, animals would receive core vaccines at least one week prior to entering a shelter. Because this is usually not feasible, vaccination immediately upon entry is the next-best practice and can provide clinically significant protection for the majority of cats and dogs. In most cases, immunity usually begins developing within hours of vaccination, and protection is often complete in as little as a few days. Thus, all incoming felines and canines should receive core vaccinations immediately upon entering an animal shelter. This is true for kittens and puppies as young as 4 weeks old—if they have baby teeth and can eat and walk, they can be vaccinated. Even injured animals, those with medical conditions, and those who are pregnant or lactating should be vaccinated on entry, because vaccination will likely be effective, and the small risk of adverse effects is outweighed by the high risk of disease exposure and infection in the shelter. When vaccination of all cats and dogs on entry is not financially feasible, the next-best practice is to vaccinate all those who are deemed adoptable at the time of entry, or are likely to be in the shelter long-term. Whenever possible, vaccinated animals should be separated from those who will remain unvaccinated.

A series of vaccinations should be administered to kittens and puppies less than 5 months old in order to minimize the window of susceptibility to infection and ensure that a vaccine is received as soon as possible after maternal antibodies have decreased enough to allow vaccine response. For kittens and puppies, vaccines should be administered every two weeks until they are approximately 5 months old. By this age, kittens and puppies should have all of their permanent incisors. This is easier to tell in puppies because the difference in size of baby teeth compared to their adult teeth is significant. Age is much harder to tell by teeth size in kittens, but body weight is usually easier to assess; as a rule of thumb, kittens can be assumed to be approximately 5 months of age by the time they reach 4-5 pounds of body weight. Beyond 5 months of age, booster vaccines are indicated one year after vaccination, and then only once every three years.

What are the Risks?

No procedure is without risk, including vaccination. The safety records for today’s vaccines are very good, but adverse reactions certainly do occur. Fortunately, most of these are minor and self-limiting. Typical reactions include lethargy, poor appetite, mild fever, or pain at the injection site for a few days following vaccination. In some cases, cats and dogs may develop facial swelling or hives and become very itchy. These sorts of reactions usually occur within six hours of vaccination, and administration of antihistamines is often helpful to curtail the signs.

In very rare instances, a pet may experience an immediate, severe allergic reaction. More severe reactions occur within the first 15 minutes following vaccination. Signs include weakness, collapse, pale to gray mucous membranes, increased heart rate, and weak pulses. Cats may vomit, have diarrhea, experience difficulty breathing, and collapse. Immediate treatment is required to prevent shock and death. In more than 20 years of practice, I have only seen two reactions like this—fortunately, in both instances, we were able to respond promptly to administer IV fluids and epinephrine, and the animals recovered remarkably quickly.

Intranasal vaccines may cause transient sneezing, nasal discharge, and mild coughing. These signs usually go away within seven-14 days. Very severe reactions may occur if intranasal Bordetella vaccines are accidentally injected. Dogs may develop local reactions, including painful abscesses, and can also develop systemic signs including liver failure, which can be fatal without prompt, aggressive treatment. Accidental injection of an intranasal Bordetella should be considered an emergency—seek immediate veterinary care should this occur.

Polyarthritis may occur in puppies and kittens following vaccination, but is usually mild and temporary. In some cases, pain relievers may be necessary to provide animals with relief from the associated discomfort until the condition resolves in a few days. In cats, the development of vaccine-associated tumors (sarcomas) may occur in as many as one in 10,000 cats. This is a serious and life-threatening condition because these tumors are malignant, grow rapidly, and are highly invasive. Current recommendations state injectable vaccines for cats should only be administered low on their legs, because if a tumor developed in this location, amputation could cure the issue. Vaccines have also been implicated as a trigger for immune system malfunctions, such as immune-mediated anemia, which can be life-threatening. Future vaccination of animals who have experienced any serious vaccine reactions should be avoided.

What About My Pets?

As with any animal or population of animals, the risks and benefits of vaccination should always be weighed in context. Pet owners should consult their veterinarian regarding a tailored approach to vaccination that meets the needs of their pets given their lifestyle and individual risk assessment. At a minimum, vaccination during puppyhood or kittenhood is the best way to ensure your pet will not contract a severe infection, including one that could prove fatal. As pets age, frequent vaccination is often unnecessary. Indeed, as with many things in life, moderation is often a good thing. n

Brenda Griffin (DVM, MS, DACVIM) is adjunct associate professor of shelter medicine at the College of Veterinary Medicine at the University of Florida.

To learn more about the current veterinary guidelines for the vaccination of dogs and cats, go to:


The Tooth About Puppy Vaccinations

puppy's teeth
  • This puppy has two permanent incisors.
  • They are the big teeth in the center.
  • The others are still baby teeth.
  • He is less than 4 months old.

This puppy will need a booster vaccine every two weeks until all of his permanent incisors have come in.


puppy's teeth
  • He now has a full set of permanent incisors. He still has his baby canines; you can tell because they’re narrow and curved.
  • He is 4.5-5 months old.

He is old enough for his final vaccine now. He does not need any more puppy boosters.


puppy's teeth
  • He now has his permanent canine teeth. They are thicker and straighter.
  • He is 6 months old now.

If he first came to the shelter at this age, he would only need a single vaccine on entry.


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