Like many people, I’ve been thinking a lot about vaccinations lately. When will everyone be able to get one? How to navigate the challenges of making appointments? Will they work well enough that life can return to something more normal? This week, I am thinking specifically about side effects . . . because I got ‘em. My first Moderna shot left me with a sore arm. No big deal. The second one laid me low. Really low. Fever, chills so bad you could hear my teeth chatter, intractable headache, insomnia, muscle aches. I kept reminding myself the benefits outweighed the risks.
This is a conversation I am used to having with pet owners. Vaccination protocols. Side effects. Efficacy. Benefit versus risk. It is particularly pertinent when it comes to cats, because of a rare but life-threatening potential side effect in kitties called Vaccine-Associated Sarcoma (VAS). Some veterinarians call it Injection Site Sarcoma, believing it may be caused by any kind of injections in cats, not just vaccinations, but I believe VAS is more accurate.
There are some basic principles of vaccinology that are useful to understand. No matter how good a vaccine is, no vaccine provides 100-percent protection for 100 percent of the population. Some pets (and people) may simply not produce an adequate immune response to provide protection. This is where “herd immunity” is helpful. Everyone understands that if enough kids in school are vaccinated against measles, the kids who aren’t vaccinated benefit from being in an environment where most of their peers are protected. The same holds true for pets. When I first arrived on the Vineyard in 1982, before there was a vaccine available for Feline Leukemia Virus (FeLV), I saw cats get sick and die from this disease all the time. Now that most people here vaccinate their cats for FeLV, I rarely see a case, even in unvaccinated cats. That’s not to say we should stop vaccinating against this deadly disease.
The official feline guidelines advise cats should be vaccinated against diseases that commonly cause significant rates of illness and/or death, and that the vaccination plan should be modified to account for an individual animal’s lifestyle. (You didn’t know your cat had a lifestyle, did you?) Thus vaccines are grouped as “core” vaccines that should be given to all cats and “non-core,” which may be selected based on risk assessment. Core vaccines for cats are rabies and FVRCP (which includes feline panleukopenia, and the upper-respiratory viruses). Some veterinarians exclude FeLV vaccines for indoor cats since infection requires direct cat-to-cat contact, but the current guidelines advise leukemia vaccines as core for all kittens. I concur. Kittens are extraordinarily susceptible to FeLV and the risk is just too great to take any chances in case your young’un sneaks out one day and gets in a scrape with a neighborhood stray.
Kittens usually need a series of three or more vaccinations starting by around 8 weeks of age. After the kitten series is completed, they should have boosters a year later, followed by boosters every one to three years depending on the particular vaccine. FeLV vaccines can then be discontinued in cats that are clearly not at risk, i.e. never going out nor being exposed to any other cat who goes outside.
The most common adverse side effects to vaccination in cats are lethargy, vomiting, and fever. (I know exactly how they feel.) Less common include diarrhea, mild allergic reactions, and pain. Very rarely an individual will experience anaphylactic shock. But starting around 1985, veterinarians began to see something far more dangerous — a connective tissue tumor at the injection site thought to be the result of chronic inflammation. We know in people that chronic inflammation may be responsible for up to 20 percent of human cancers. That’s why our dermatologists are always bugging us about protection from sun exposure. So what happened in 1985 with cat vaccinations that might have led to this problem?
Simple. Cat vaccines changed. The “modified live virus” (MLV) rabies vaccine was found to be problematic. Every once in a while, the modified virus modified back, and the vaccinated animal got rabies from the shot. The MLV rabies vaccine was discontinued and replaced with a “killed adjuvanted” vaccine. This product had no live virus in it, but also contained additives called adjuvants that essentially work as irritants to stimulate the immune system’s response. At the same time, killed adjuvanted FeLV and FVRCP vaccines were also introduced. Gradually veterinarians recognized a new problem. Some cats would react to a vaccine by developing a highly aggressive malignant cancer. This was heartbreaking to both owners and veterinarians, who were just trying to protect their patients.
Studies indicate that vaccine-associated sarcoma has both genetic and environmental causes. Some cats are just more likely to develop inflammation-associated cancer. Adjuvanted vaccines cause more inflammation than MLV ones. Statistics eventually determined that killed adjuvanted vaccines were a mean of 10 times more likely to result in VAS than recombinant vaccines in cats! Then a wonderful thing happened. They developed recombinant vaccine technology and made effective feline vaccines that were neither MLV nor adjuvanted.
Since we cannot test for or control a cat’s genetic predisposition, what we can do is reduce the environmental risk by using the least inflammatory product available, and not over-vaccinating. Current feline vaccination guidelines strongly advise avoiding adjuvanted vaccines whenever possible. Having seen a few cats lose their lives to VAS, I agree with the radical wing of feline practitioners who feel no adjuvanted vaccines should ever be given to cats. So if your veterinarian is using what seems to you to be a very expensive recombinant vaccine, remember it is probably because this is the safest option for your cat. By the way, I’m feeling much better this morning. Thanks for asking. I’m grateful to be vaccinated. Now hoping jabs soon become available for everyone in my family, all my friends, my fellow Islanders, and everyone else everywhere. The benefits outweigh the side effects. No doubt about it.