Cat Health News: Cancer from Vaccines
A feline vet dishes on the evidence between cat vaccines and sarcomas.
Gary D. Norsworthy, DVM, DABVP
Vaccine-associated sarcomas, as they were initially called, were first reported in 1991 by a veterinary pathologist who diagnosed an increasing number of malignant tumors that had occurred at vaccine sites. This followed three significant events.
Many cat tumors have occurred at sites where non-adjuvanted vaccines occurred. As more data emerges, the name of these tumors should go from "vaccine-associated sarcomas” to "injection site sarcomas.”
These three events resulted in thousands of cats receiving vaccines for the first time and for thousands of cats that were vaccine-delinquent getting boostered. It is estimated that at least ten times more cats received vaccines from 1985 to 1990 than in any other previous five-year period.
- In 1985 all modified live virus rabies vaccines were replaced by killed rabies vaccines by government mandate. In order to make the immune system respond to a killed virus, an agent is added that gets the attention of the immune system; it is called an adjuvant and is necessary in all killed vaccines.
- The same year, feline leukemia virus vaccine was introduced; it was also a killed vaccine with adjuvant.
- In the same time frame there was an outbreak of rabies in wildlife and pets in the Northeast. For the first time, several states required that cats receive rabies vaccine.
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The Problem With Blaming Vaccine Adjuvants
Initially, the adjuvant in the killed vaccines was blamed for these malignant tumors; this seemed very plausible at the time. However, pathologists of the day noted that these tumors had been recognized for many years, but they occurred in much smaller numbers. They also noted that vaccine adjuvants had been used for many years, so the change that occurred was more likely due to this sudden increase in vaccination in cats.
When discussing vaccine adjuvant, the conversations and investigations centered on inflammation. In order for an adjuvant to get the attention of the cat’s immune system, it must create some inflammation. The focus of interest and research in the 1990s was on how this adjuvant-induced inflammation could result in tumor formation. It seemed very plausible at the time; however, over the next 10 to 15 years of research, there were two problems that emerged with this hypothesis.
First, some of these malignant tumors were documented to occur at injection sites unrelated to vaccines. Several agents, including antibiotics and steroids, could be linked to tumor formation. More recently, the terms "spontaneous sarcomas” and "induced sarcomas” are gaining acceptance within the veterinary medical community. These terms are particularly fitting because sarcomas can arise spontaneously at sites not used for injections, such as in the mouth, and they can arise at obvious injection sites.
A Genetic Mutation Could Be to Blame
The second problem with blaming vaccine adjuvants for these tumors is their incidence of occurrence. Several epidemiological studies have been performed looking at very large numbers of cats across the country. The consensus rate is currently accepted to be approximately one sarcoma in 10,000 cats that receive vaccines. Thus, more than 99 percent of cats receiving adjuvanted vaccines never get tumors. This means that instead of blaming the vaccines, we need to realize that a very small number of cats are somehow predisposed to this problem. The best explanation for this is the genetics of the cat. It is well documented that mutations occur with aging in cats and other species, including humans, and these mutations make these individuals predisposed to many kinds of cancers. This explains why cats will receive vaccines and other injections for many years without sarcoma formation, and then one occurs later in their lives.
Another strong evidence for a genetic basis of this problem is the occurrence of two sarcomas in the same cat. I have had this occur in two of my patients. Each received vaccines followed by a sarcoma at the vaccination site a few months later. About one year after the tumor was surgically removed, the cat received another vaccine at a distant site and another sarcoma occurred at the new site. Clearly, there is something different about cats like this, and that is best explained by a genetic defect.
When injection site sarcomas first occurred, there was panic among veterinarians and cat owners alike. Veterinarians were horrified to think that something they did resulted in cats getting cancer. Cat owners were equally horrified and incensed that something their veterinarian did resulted in their cats dying. Understandably, these fears translated into many cat owners refusing to have their cats vaccinated for rabies or for any disease. Many cat owners whose cat developed one of these tumors could never be convinced that the problem was anything but the vaccine. They could not even imagine that something within their cats (a genetic mutation) could be to blame. These incensed cat owners were usually very vocal about the problem and told all of their cat-owning and Internet friends. Thus, vaccines have been demonized and rejected by many cat owners.
Tragic Decline in Veterinary Wellness Examinations
The greatest tragedy that has come from this controversy is the loss of annual wellness examinations for thousands of cats. When vaccines are rejected, many cat owners no longer allow their veterinarian to even examine their cats for "preventive maintenance.”
When I do an annual examination, I see this primarily as an opportunity to find disease early and intervene when intervention is possible and will likely produce a positive outcome. It is a time when I can share the latest news about diet, heartworm prevention, and heart, kidney and thyroid disease, etc. I have saved thousands of feline lives because I have been given the opportunity to do a wellness exam. Unfortunately, most cat owners who have decided not to have their cats vaccinated again, no longer give their veterinarian the opportunity to do this life-saving examination.
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Cat Health News: Cancer from Vaccines