Years ago, dogs and cats were routinely vaccinated against just about anything we could vaccinate them against on the off chance that the pet might be exposed to that disease, in which case the vaccine should protect the pet. Today, we recognize that vaccines can sometimes have a downside as well. There can be side effects with any medication and vaccines are no exception.
Vaccination Sarcomas and Cats
When rabies vaccination became mandatory for cats in many communities, the veterinary profession also began to recognize that we were seeing an increased incidence of a specific type of tumor called a sarcoma in cats. Research and retrospective studies over time revealed that the increase in the incidence of sarcomas was found to parallel the increase in rabies vaccines administered to cats.
Currently, it is believed that sarcomas may occur as a reaction to any feline vaccine, but rabies vaccines and feline leukemia vaccines are thought to be more likely to have an association with sarcoma formation than other feline vaccines. This discovery led to a rethinking of the previous vaccination protocols for cats.
- It is no longer recommended to vaccinate all cats for feline leukemia but rather only those that are at risk of exposure to the disease.
- Because of the threat to human health with rabies, not vaccinating cats against rabies is not an option. However, newer and safer vaccines against rabies have been developed and vaccination protocols have been changed, although the individual protocol varies depending on the vaccine.
Anaphylactic/Allergic Reactions to Feline and Canine Vaccination
By far the most common adverse reaction to vaccinations in both dogs and cats is an allergic reaction.
- A normal reaction to vaccines includes mild lethargy and soreness. A mild fever may also occur and these symptoms are generally not serious.
- Vaccine reactions in dogs and cats can occur directly after the administration of a vaccine or within 48 hours later.
- Hives, swelling of the face, muzzle and ears and sometimes nausea are symptoms seen with an allergic reaction.
- In more severe cases, the dog or cat may go into shock and may also die suddenly. Fortunately, this complication is extremely rare.
What Pets are Most Likely to Have Adverse Reactions to Vaccines?
Puppies and kittens and young cats and dogs are most likely to suffer adverse reactions to a vaccination. Small breeds of dogs are more likely to be affected than larger breeds.
Administering multiple vaccinations at the same time is more likely to elicit an adverse reaction also. However, interestingly, multi-valent vaccines (vaccines which protect against more than one disease in the same vaccine) do not appear to cause an increase in the incidence of adverse reactions.
Are Some Vaccines More Likely to Cause Allergic Responses in Pets?
Yes, some vaccinations, including leptospirosis and Lyme disease vaccines, have been found to be more reactive than other vaccines. However, at least in the case of leptospirosis, newer vaccine technology may have eliminated this risk as one study performed recently did not find an increased incidence of adverse reactions in puppies and dogs vaccinated with one of the newer leptospirosis vaccines.
Immune-Mediated Disease Linked to Vaccines in Cats and Dogs
At this time, the link between immune-mediated disease and vaccinations administered to dogs and cats is unclear. However, there is some evidence that vaccinations can at least predispose a pet to developing immune-mediated disease. More research is needed in this area but there is some concern that vaccination could have a long-term effect on the immune system, making it important to minimize unnecessary vaccinations.
Vaccine Preservatives, Mercury and Thiomerosal in Canine and Feline Vaccines
Some vaccinations contain various preservatives, including mercury and thiomerosal (a compound containing 49.6% mercury by weight). Preservatives are added to vaccines in order to reduce the potential for growth of micro-organisms such as bacteria or fungi in the event of an accidental contamination of the vaccine vial. It should be noted that not all vaccines contain mercury or thiomerosal however.
In human medicine, there have been concerns raised about the safety of mercury and thiomerosal in vaccinations and that these substances may be linked to the development of the development of autism or other neurodevelopmental disease. However, studies performed to investigate this causal relationship have failed to prove there is a positive correlation, according to the FDA publication Questions About Vaccines. Similar studies in animals have also failed to show a link between adverse reactions in pets and mercury or thiomerosal-containing vaccines to date. This continues to be a controversial and widely debated topic, however.
Adjuvants in Vaccines for Dogs and Cats
Adjuvants are substances that are added to vaccines to increase the body’s response to the vaccine and lead to better protection with smaller quantities of the biological portion of the vaccine. Adjuvants have been implicated in causing cancer in pets. This is another reason that unnecessary vaccinations should be eliminated from the vaccination protocol for individual animals. Currently, some vaccinations are manufactured that are free of adjuvants and many veterinarians consider these safer than adjuvanted vaccines.
Why Administer Vaccines to Dogs and Cats with the Risks Involved?
Despite the risks involved with vaccinating dogs and cats, vaccines still provide documented benefits which in most cases outweigh any risks involved with their administration. However, vaccines protocols for an individual animal must assess the relative risk for that animal and only vaccines which can claim the potential for more benefit than risk should be administered.
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Lorie, thank you for this article!
I have few more questions
1) if sarcomas in cats are independent of the type of vaccine; wouldn’t it be safe to assume that it is not the antigen itself, but rather one of the other ingredients such as the mercury or the adjuvant?
2) anaphylactic shock is one of the reactions that would occur shortly after administration? Or can that also happen within 48 hours later? If so, anything one could do? Would it make sense to ‘rent’ an epi injection after vaccination?
3) Good news on the multi-valent vaccines. Wouldn’t that also support the theory that it is not the antigen but the additives that cause all the problems? Since I’m assuming that multi-valent vaccine = 1x additives, while multipe vaccines = Xs addtitives?
4) regarding immune-mediated disease, I find IMHA the most scary and some experts link that to vaccines, rabies specifically.
Anybody tried to figure out why? One question that comes to mind, other than the additives: very few infections involve direct introduction into blood, except things like rabies and tick born disease and disease transferred via mosquitoes.
I read reasoning that most infections get introduced to mucus membranes first, which provide first line of defense. Would by-passing this first line of defense contribute to the negative effects?
5) I was always under the impression that mercury was one of the most potent poisons. I imagine that the amount present in a vaccine is very small. Does the body have the capacity to eliminate the mercury from the system or does it remain lingering? If eliminated, would it cause damage to kidneys or other organs? Wondering about the cumulative effect.
6) what substances are used as adjuvants?
7) what is the difference about efficacy of a vaccine with and without an adjuvant?
Hi Jana.
You’re very welcome for the article.
You ask some very important questions here and, because they are important questions and other people are likely to have the same or similar questions, I will answer them in a separate post within the next few days.
Thank you! And no, I don’t hate you yet
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