Vaccines,What are the Risks and Benefits to Your Pets.
As a veterinarian I am faced with questions about vaccinations every day, what are the risks? what are the benefits? To say that vaccines are safe is true, however there are adverse effects associated with vaccination. While extremely rare, anaphylactic allergic reactions can occur and must be dealt with immediately. Other allergic reactions, fever, vomiting, facial swelling occur on occasion, but are still rare. The old feline vaccinations were associated with development of an injection site sarcoma; this occurred more commonly in patients with a genetic predisposition to cancer. So yes there are some risks associated with vaccination. When it comes to vaccination, we have to assess the relative risk of vaccination vs. the risk of the disease. Rabies vaccine however is always indicated as it is state law to vaccinate dogs and cats. Most pets however, do not have the social risk factors of humans, there are some such as those that go to groomers, boarding kennels, and day care. These pets have risk factors more like us, where we go to work, school, shopping; where we interact with others that may or may not be vaccinated or be incubating or spreading a contagious disease.
When an animal or person is vaccinated, most will form antibodies to the false infection that will protect from the real infection when the subject is exposed to the pathogen. There are however, some individuals that are genetic non-responders, meaning they cannot form antibodies to the vaccine. These are the individuals that get sick despite vaccination. This happens in canine parvovirus on occasion because the dog, no matter how many times they have been vaccinated, simply cannot respond to the presented antigen. So how do we protect these “non-responders” in the population, along with the individuals that cannot receive vaccines because of illness, immunocompromise, or allergies. The key is a concept called herd immunity, and it derives from infectious disease management mostly in the cattle and dairy industry. The more individuals that are vaccinated, the more protected the herd, including those that cannot be vaccinated or are non-responders. The more individuals that do not receive the vaccine, the more likely the herd immunity will fail and an outbreak will occur.
Measles is a virus that belongs to a group of viruses called Morbillivirus. It evolved from a cattle virus called Rinderpest around 1100-1200 A.D. When the measles virus first adapted to infect humans, it had a high mortality rate, killing up to 60% of those infected. Over time, the virus (and us) have changed to be less fatal, but still is very infective. It is interesting to note that Rinderpest, the cattle morbillivirus, has been eradicated by a global vaccination protocol, similar to what we did with the Smallpox virus in humans, and almost did with the Polio virus until the Taliban in the tribal areas of Pakistan started shooting the vaccinators. The canine morbillivirus causes a disease called distemper, which most veterinarians in practice today will never see because enough people continue to give their dogs the vaccine to keep herd immunity up and individuals protected by a highly safe and effective vaccine.