There is a lot of new information out there on vaccinations, such as DHPPC, that is causing veterinarians and concerned clients to question, “Is vaccination really necessary for my pet and how often?” Other questions that pet owners have are, “What could happen if I do not give my pet vaccinations?” Additionally, “How many and what types of studies have been done to research this?”

While these are very simple questions, unfortunately the answers are very complex. Before we try to answer this question, let’s address some of the factors involved: individual protection, herd health immunity, how vaccines stimulate the immune system, individual immune systems, and potential vaccine reactions.


Individual immunity is the concept of individual protection based upon vaccines given. Generally, vaccines are not considered 100% effective. Vaccines today are rigorously tested to demonstrate better than 98% protection. However, with repeated booster vaccines, an individual is protected from those diseases (please see individual immune system below).

Herd health immunity is a concept based upon the premise that the number of individuals in a population who are vaccinated against a particular disease is inversely proportional to the severity of a potential epidemic.

Example 1

People are no longer being vaccinated against Small Pox. Therefore, there are very small numbers of protected individuals from this disease. If this disease is reintroduced into the United States population (by a terrorist), we will have a major epidemic on our hands.

Example 2

The majority of our pets are routinely vaccinated for Rabies. Texas is always at risk of exposure to this disease because we border Mexico. Reported cases of Rabies are few in number because the majority of the population at risk are protected. Although some individuals may be at risk, there is very little possibility of an epidemic.

How Vaccinations Stimulate the Immune System

Each puppy and kitten receives maternal antibodies from the mother, both through the placenta and also in the colostrum (the first milk). This is termed “Passive Protection” and the strength of these antibodies is dependent upon the strength of the mother’s immune system. The mother obtains these antibodies from prior vaccination or by natural exposure to disease. Maternal antibodies are a two-edged sword; they may protect the puppy against disease early in life, but they also interfere/block the young animal’s response to vaccinations or active immunization. These maternal antibodies can interfere with vaccination for as long as 14 to 16 weeks in some puppies and kittens.

A refractory period can exist in some puppies or kittens where very low, almost undetectable levels of maternal antibody will inhibit the vaccination process, but will not protect the puppy/kitten from infection (from exposure to the natural virus). To determine the exact time at which this refractory period occurs is very expensive. Therefore, a SERIES of vaccinations is the most inexpensive and best way to protect puppies and kittens against disease, insuring vaccination at the best time. It is important to begin vaccinations at an early age and repeat every 3-4 weeks until the putty or kitten is at least 16-18 weeks old.

Immune System

Puppies and kittens in general do not have a very strong immune system. It can take pets up to 6 months or even a full year before their immune system is considered fully functional. Because of the interference from the maternal antibodies, veterinarians do not begin the vaccination series until the pet is six to eight weeks of age. The vaccines are then boostered at three to four week intervals until the pet is sixteen to eighteen weeks of age.

Because of the different strengths of response each puppy and kitten will have to vaccination, they can still be highly susceptible to infection until 2-4 weeks after the last injection of the immunization series.

Vaccines do not cause a disease, but act as a stimulus to your pet’s immune system, causing it to produce antibodies capable of protecting your pet against those specific diseases. Antibodies fight disease by killing disease-causing organisms within the body.


The timing between vaccinations is extremely important. Antibody levels produced by the initial vaccination diminish with time. When your pet is re-vaccinated, his or her immune system is stimulated to “remember” the specific disease organism and manufacture more of the appropriate antibodies. Memory cells affect the strength and speed of the immune system’s response to infection. The amount of memory is dependent upon the timing of the vaccinations. After the first vaccination, an immune response occurs.

The strength and length of this response is similar to a “bell curve” with the strongest response (peak) occurring within a month of the vaccination. After a month, the numbers of ‘memory cells’ diminish. When your pet receives his second vaccination within a month of his first one, a much stronger response (and therefore memory) is stimulated. However, if the time until the second booster vaccination is longer than a month, then the amount of immune response is much the same as the first vaccination.

By the time your pet’s third or fourth booster is given at the appropriate time intervals, your puppy or kitten will have a much strengthened immune response (antibodies) to that specific disease. Because of these developed antibodies (with the full series of booster vaccinations), the pet will then only need booster vaccinations at various intervals (time is dependent upon type of vaccine) to keep the memory cells (antibodies) replenished.


The health of an individual’s immune system is dependent upon many variables. Like people, pets have varying abilities to respond to vaccines and fight off infections. Some scientific studies have demonstrated that some pets have a very strong immune response and may not need vaccinations on a yearly basis. This is very similar to how the human immune system works. However, other scientific studies have demonstrated that some pets never achieve complete protection (immunity) from certain diseases, even with repeated booster vaccinations.

Vaccines are not guaranteed to prevent disease because too many variables are involved. Very young puppies and kittens, as well as aging pets, appear to have diminished ability to respond to vaccinations. In such cases, it is critical that the pet be re-vaccinated at the appropriate interval. An animal that is underweight, pregnant, or stressed because of a serious infestation of parasites or other illness also may respond poorly to vaccination.

The following is a short list of variables that can have major impact upon an individual’s immune system:

  • Age of the pet Very young puppies and kittens, as well as aging pets, appear to have diminished ability to respond to vaccinations. Their immune system is not fully functional. Pets between two and six years of age have the best immunity of their life and, if their immune system is not compromised by any stresses, probably have less need of vaccinations to keep their immune system healthy.
  • Strength of individual immune system As stated above, each individual has variable strength in their immune system. We all know certain people who seem to never get sick, while there are other individuals who get sick quite frequently. The same is seen with our dogs and cats.
  • Major surgeries Any pet undergoing major surgery, from ovariohysterectomies to fracture repairs (Hit By Car), suffers considerable stress to its immune system and that pet’s ability to fight off infections is lowered.
  • Major illnesses A healthy immune system is one which is not challenged or lowered by stresses to the body. Illnesses such as diabetes, liver disease, heart disease, and kidney disease severely suppress the immune system. Even simple urinary tract infections can affect the health of a pet’s immune system.
  • Parasites such as hookworms or heartworms will depress the immune system. Heartworm treatment has a major effect on the liver, kidneys, and lungs and can severely suppress immunity.
  • Poor nutrition obviously affects every aspect of your pet’s health.
  • Frequent boarding, grooming, and attendance at dog shows also cause repeated stress and lower the immune system’s abilities.


If an animal is exposed to disease shortly before or after vaccination, it may not have sufficient time to develop immunity from the vaccination before it becomes sick. This often occurs in pets adopted from shelters where they have been exposed to all sorts of diseases (many of these diseases are not the fault of the shelter as many of them are air-borne). Remember that it takes time for a disease to develop after exposure, and the vaccine may not have enough time to activate the pet’s immune system if the disease is already working in the pet’s body.

However, if an animal has been previously vaccinated for a disease that it is later exposed to; re-vaccination will result in faster immune response resulting in protection of the pet in less time than it takes for the virus to cause disease.

Potential Vaccine Reactions

There is less than 0.05 percent chance of a pet having an adverse reaction to a particular vaccine. This reaction is usually caused by the adjuvant which is in the vaccine to stimulate the immune system.

Common Reactions

Cats can have a severe, sometimes fatal, reaction to vaccinations. This type of reaction happens less than 0.05 percent of the time. They have an anaphylactic response—vomiting, diarrhea, salivating, and walking off-balance as if they were drunk. This response usually occurs within fifteen to thirty minutes, but we caution owners to observe their cat for a few hours after vaccination. Sometimes cats will just feel poorly and be lethargic the day following vaccinations.

Because of the potential severity of the reaction, our hospital does not change the type of dog and cat vaccines used. This way, we know how our pets will react based upon previous vaccination. However, we do like clients to observe their pets after each vaccination because occasionally the drug companies will improve (and therefore change) their vaccines.

Dogs can have three different types of vaccine reactions:

Anaphylactice response—what we like to call the collapsing puppy syndrome. This happens less than two percent of the time and is usually within ten to fifteen minutes.

Allergic response—with this reaction, the eyelids, nose, lips, and face puff up and the dogs get lumps (hives) all over their body. This reaction can occur within fifteen to thirty minutes, one to two hours later, or six to eight hours later. This reaction usually responds very well to Benadryl.

Delayed cellular response— lumps on your dog’s body can appear where vaccines are given. This lump may occur within one to three weeks of the vaccination, is usually non-painful and may take one to two weeks to go away.

Rare Reactions

Part of the controversy surrounding vaccines involves the possibility of vaccine associated tumors and auto-immune disease.

Feline Vaccine Associated Sarcomas first came to our attention over 20 years ago. It occurs in less than four in 10,000 cats from vaccinations (an injection of any type can potentially cause a sarcoma). It is now believed that there is a genetic component involved in development of the tumor. 

Our hospital uses non-adjuvanted vaccines, which are less likely to cause reactions.  The diseases vaccinated for can lead to severe and even fatal consequences (for example, Feline Leukemia and Rabies).  The risk/benefit ratio of possible vaccine reactions must be weighed against the known risk of disease.  Vaccines are also recommended on an individual basis, resulting in fewer numbers of unnecessary vaccinations. For more information on this reaction, please refer to our Vaccines and Sarcomas Handout.

Autoimmune Disease

Autoimmune disease can occur in dogs for a number of reasons – genetic/hereditary, viral or bacterial infection, drugs, and vaccines. It is estimated to occur in less than four in 10,000 dogs because of vaccinations. Autoimmune disease can also be brought on by numerous causes other that just vaccines, so it is difficult to implicate vaccination as a definitive cause in these cases.  The diseases vaccinated for can lead to severe and even fatal consequences (for example, Parvo, Distemper and Rabies).  The risk/benefit ratio of possible vaccine reactions must be weighed against the known risk of disease.  Vaccines are also recommended on an individual basis, resulting in fewer numbers of unnecessary vaccinations.

Vaccine Protocols


DHPPC—Distemper, Hepatitis, Parainfluenza, Parvovirus – This vaccine needs to be given as a part of the puppy series (booster vaccines 3 weeks apart from 6-18 weeks of age) and again at 12 months of age. It will then be given once every 3 years unless indicated otherwise based upon the needs of the pet.  It is required at our hospital for all boarding, surgical and dental patients.

Bordetella (Kennel Cough)—This vaccine is to be given at 3-4 months of age and boostered annually. It is required at our hospital for all boarding, surgical and dental patients.

Rabies—Per state law, this vaccine is to be given at 4 months of age, 12 months later and then every 3 years using a 3 year vaccine. Rabies is fatal not only to animals, but also to people!  It is required at our hospital for all boarding, surgical and dental patients.

Canine Influenza—Compared to the others, this is a relatively new disease.  There are two strains that are currently vaccinated for.  The vaccine is given two times (2-3 weeks apart) and then on an annual basis.  Recommendation of this vaccine depends upon your pet’s lifestyle and possible exposure to other dogs.  It is required at our hospital for all boarding patients.

Lyme—This vaccine is recommended annually for those dogs exposed to ticks. Not all dogs need this vaccine. It is our strong recommendation that all dogs at risk of exposure to ticks be placed on tick repellant/insecticidal products.

Leptospira—This vaccine is primarily recommended for hunting, working, and outdoor/rural dogs.  However, some indoor dogs have also gotten this disease.  Leptospira is contagious to people. Unfortunately this vaccine does not protect against all of the serovars (sub-types) of this disease and therefore your dog cannot be considered fully protected from this disease from vaccination alone.  Infection occurs after exposure to water contaminated with urine from infected wildlife.


FVRCP—Feline Viral Rhinotracheitis, Calicivirus, Panleukopenia This vaccine is to be given to all cats every 3 years following their kitten series (booster vaccines 3 weeks apart from 6-18 weeks of age) and a booster every 3 years.  It is required at our hospital for all boarding, surgical and dental patients.

Rabies— according to state law, this vaccine is to be given to your pet at 4 months of age, 12 months later and then every 3 years using a 3 year vaccine or annually using a 1 year vaccine.  It is required at our hospital for all pets that are boarding, or have surgical or dental procedures.

FeLV—Feline Leukemia Virus This vaccine is recommended for all outdoor and indoor/outdoor cats on an annual basis following kitten series vaccinations.  After their initial kitten series, indoor cats and cats not exposed to indoor/outdoor cats do not need to receive this vaccine.

FIV—Feline Immunodeficiency Virus This vaccine is recommended for all outdoor cats and indoor/outdoor cats on an annual basis following kitten series vaccinations. Cats will need to be tested for FIV infection prior to vaccination.

Like any reputable hospital, we require vaccinations prior to boarding and surgery, but we do not require that patients get them from us. We’re happy to accept them from any licensed veterinarian/veterinary hospital.  We do not accept feed store or other vaccines given by non-licensed individuals.  We truly believe that regular vaccinations are extremely important in ensuring your pet’s well-being.

Other Protective Measures

Do not take your young puppy/kitten to the front yard, park, around the block, or to PetSmart or PetCo until he or she is 4-5 months old. These are all places where infectious animals can be or have been.

Only have the young puppy/kitten around adult animals that you know are current on vaccinations. There should be no contact with stray animals or animals that you are not sure of.

Do not let your puppy (kitten) be exposed to any other young puppies (kittens), even those coming to our hospital to receive vaccines. These animals could be incubating disease (and therefore be contagious) without showing any clinical signs of illness.

Always wash your hands after handling any animal.

The Veterinary Visit

When bringing your puppy/kitten to a veterinary hospital for it’s series of vaccines, we recommend that you do not let the pet walk around on the ground. While we take protective measures to decrease exposure to disease, we cannot guarantee 100% effectiveness of these measures and we do have sick animals that owners will walk outside the hospital.

We strongly recommend physical examinations twice a year on your pet. Our pets age more rapidly than we do. More frequent examinations will help us to achieve early detection of hidden health problems and make it easier to manage them, effectively lengthening your pet’s life and also improving his/her quality of life.

Please do not hesitate to talk with one of our Doctors, should you have any concerns or questions.