Pet Connections

The Power of the Shot – How Vaccines Save Pet Lives

By Becky L. Morrow, DVM

As a pet parent, I’m sure you have gone to the vet to get your dog or cat her “shots,” but do you know how they protect your pet or what diseases are being prevented? Being a shelter vet and facing the reality of outbreaks that can wipe out entire populations gives me a unique perspective on how many lives can be saved by vaccinating.  Before we discuss what diseases the vaccines are protecting your furry family members against, let’s cover how they work, in general, and why puppies and kittens need so many “boosters.”  

Vaccines essentially “trick” our immune system into thinking a foreign invader, usually a virus, has entered the body.  While it seems rude to prank our immune systems, there is a very good reason for doing so.  After the immune system builds up defenses to “fight off” the perceived “infection,” it remembers the invader and can respond much more rapidly in the future when the real virus attacks.  It would be like the FBI having a picture of a criminal and using facial recognition software to stop him right after he enters the door – before he can do any harm.  Because law enforcement knows what the intruder looks like ahead of time, they have a whole team of officers ready when he breaks into the building.  The police force represents the antibodies and specialized cells that are standing and waiting to respond to a pathogen after the individual has been vaccinated.  Without vaccines, it would be like the criminal enters the building with no one to stop him.  Not only that, more and more criminals keep entering, unchecked.  They may be eventually stopped by the police force, but not before they caused destruction of the property.  

So why do we give puppies and kittens (and babies!) a series of booster shots?  The reason is that young animals have some limited immunity that they acquired, mainly through nursing, in the form of “maternal antibodies.”  While the maternal antibodies are present, they will fight off the invader before the puppy or kitten can develop their own immune response (antibodies and specialized cells that will attack).  Since there is no way of knowing exactly how long the maternal antibodies will remain active in the system, we need to keep giving the booster shots until an age where we know they cannot interfere with the vaccine working.  

Typically, in puppies and kittens with homes, we give booster shots every three to four weeks until about 14 weeks of age, but in shelters and rescues, where the risks of exposure to infectious diseases are much higher, we give boosters every two weeks (the shortest time between vaccines that will still give a full immune response) and for a longer duration.  In some cases, as with the rabies vaccine, there is not a booster until one year later, mainly because it is not given until a bit later in the pet’s life (12 weeks of age in most cases based on Pennsylvania state law).  

Now let’s talk about the core vaccines that all pets need.  Rabies is certainly a disease that everyone knows about.  It is invariably fatal, and all animals need to be protected against it for their benefit as well as the benefit of humans.  Rabies vaccines either contain “killed virus” and a chemical called an adjuvant to cause the immune system to take notice, or a recombinant vaccine, where a small piece of the rabies virus is connected to a harmless virus that allows the immune system to respond without illness. After the initial one-year booster, the killed vaccine can be administered every three years, while the recombinant vaccine may be boosted in one to two years.   

What is often called the “distemper vaccine” for dogs and cats is actually very different in each species.  The core vaccine for dogs, often abbreviated as DA2LP2, helps to protect them from canine distemper virus, canine parvovirus, leptospirosis, canine hepatitis, and upper respiratory viruses (adenovirus and paramyxovirus).  Distemper and parvovirus are especially frightening for a puppy or even an unvaccinated adult dog to get since they are oftentimes fatal infections.  Even with intensive care dogs can die from the respiratory, gastrointestinal, and neurological disease associated with distemper and the vomiting and diarrhea that leads to blood infections and severe dehydration.  Leptospirosis causes kidney and liver disease and can also infect humans, another important reason we vaccinate animals against it.

Feline “distemper” vaccine, or FVRCP, includes protection against feline viral rhinotracheitis (or feline herpesvirus), feline calicivirus, and feline parvovirus.  Just as with the canine parvovirus, feline parvovirus (also called panleukopenia) causes vomiting and severe diarrhea that can lead to death through septicemia (bacteria in the blood stream) and dehydration.  Parvoviruses are highly contagious, requiring only a small amount of virus that is passed in the stool for exposure.  Unfortunately, parvoviruses also can remain infectious in the environment for many, many months.  Just like with the human flu shot, a cat vaccinated against calicivirus, and herpesvirus can still get infected, but tend to have much less severe symptoms.

Other non-core vaccinations can be selected based on specific risk factors for your pet.  Some owners choose to get a Lyme vaccine for their dog if they have problems with ticks.  Many people have their dog vaccinated against “kennel cough,” which includes protection against the bacteria, Bordetella bronchiseptica, as well as the upper respiratory viruses.  As the name implies, it is mainly for dogs going to kennels or doggy daycares and is very important in shelters as well.  Although mostly used in shelter settings, some kenneled dogs are also vaccinated against canine influenza, a virus that can cause respiratory infections including pneumonia.  Cats that go outdoors or have potential exposure to cats with an unknown FeLV status, should definitely be vaccinated against feline leukemia virus.  This is a fatal disease in many cats, that is easily preventable.  Although there is a vaccine for FIV and FIP, neither vaccine is recommended by specialists or the vast majority of veterinarians.

While this article is just a brief overview of the topic, I hope it gives you a better understanding of vaccines and how they can keep our pets healthy.  Remember to talk to your veterinarian to determine what is right for Fluffy or Fido based on their health status and risks.


December 14, 2023
December 14, 2023


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November 21, 2023