Possible problems associated with feline vaccines


The Purevax (tm) rabies vaccine reaction

Question: Dear Dr. Mike, I am really in need of your expertise. I took my kitty to the vet for his annual rabies shot. He had an allergic reaction 36 hours after being vaccinated with the new Purevax rabies vaccine from Merial. He went into shock and coma and stopped breathing. My vet managed to bring him around, but he was very ill from that time on. He developed excessive thirst and high glucose (my vet thought possibly type 2 diabetes. I tried insulin and diabetic food unsuccessfully) and then a couple of months later liver complications (infection), potassium deficiency, thyroid trouble, severe limp, muscle wasting, and liking for cold. He also would stare into space like he didn't see anything, and seemed to wander around restlessly at all hours of the day and night. It was like his immune system was completely destroyed from something in the rabies shot. He had never been ill prior to this in the eight years I'd had him! The last couple of months I was giving him three sets of pills morning and evening (potassium supplements and appetite stimulants) and was finally force feeding him three times a day. His weight dropped from 14 pounds to around 5 pounds. He just stopped eating and went into a coma at the end before he died. I've discovered on the Internet four other people who have had problems with this vaccine (3 cats died). My question is, do you know anything about the Purevax rabies product or why this all happened? My vet assured me the vaccine was safe and that it could even be used with kittens. Although I feel I did everything possible, I still feel terribly guilty that I took him for his vaccination and that I chose this product. If I hadn't, my kitty might still be here, alive and well. Please let me know your thoughts about this and whether you've heard anything else about the Merial vaccine. Thanks, Linda

Answer: Linda-

The Purevax (tm) rabies vaccine is a "recombinant" vaccine. It is made by inserting a portion of the rabies virus into a canarypox virus to cause immunity, without having the whole rabies vaccine present. This allows it to be a live virus (the canarypox), which can proliferate and this produce strong immunity, without the risk of rabies ever developing, as has occurred in the past with modified live vaccines made from rabies virus. This means that the vaccine can be produced without the need for adjuvents as are necessary for killed vaccines. This should reduce the risk of vaccine associated sarcomas (cancer at vaccination sites) which can occur in cats. This is the reason that veterinarians like this vaccine and probably is part of the reason that acceptance of the new technology of using the canarypox virus in a vaccine for cats was accepted quickly by veterinarians. This is a web page of Merial's, with an explanation of how these vaccines work:


I could not find a listing of adverse reactions for Purevax on the USP web site or the USDA web site. This does not mean that they don't occur. It is a relatively new vaccine and it may take some time to compile statistics for reactions.

I talked to our Merial represenative and he told me that about 4% of cats have fevers after vaccination with Purevax (tm) and that the fever can be high in some cats. This seemed to be the extent of the reactions that the representative was familiar with, although I have seen at least one report of an anaphylactic reaction to one of the canarypox recombinant products and we feel that this has happened once in our practice, as well..

It is possible that the reaction to the vaccine could be coincidental or that a secondary problem surfaced due to stress from a vaccine reaction that might otherwise have been mild. However, it is important to report any possible vaccine reaction to the manufacturer and it is a good idea to report it to the www.usp.org web site, as well.

I wish that I could provide a definite answer to your question. It is difficult to be sure that the vaccine was the sole reason for the problems that occurred but it may have been. If it was, asking your vet to report the reaction may help to provide some idea of how frequently reactions occur and make it possible to make a better assessment of the risks associated with the vaccinations so that they can be compared to the expected benefits for a better risk vs. benefit assessment.

I don't think that you are being fair to yourself in feeling guilty about this vaccine choice. The best evidence at this time suggests that the recombinant vaccines are less likely to cause vaccine associated sarcomas and the reported reaction rate is low. It is not possible to predict in advance which animals will have adverse reactions, so you could not have known this would occur. It is an example of making the right decisions, doing the thing that seems most correct and still having a bad outcome. These reports sadden me, because it is so important to try to make good decisions and I hate it when making the effort to do so still has a bad outcome. I hope that the fact that your motivations were good and that your veterinarian's motivations were good will eventually allow you to accept that you did the best you could at the time and allow you to move on and reach the good memories that you have of times spent with your cat.

Mike Richards, DVM 9/28/2001

Vaccination reaction

Q: Last Monday and Tuesday I noticed that my cat, Christine, had a small amount of mucousy blood in her stool. She had no other GI problems or problems otherwise. I called the vet and said, that due to our recent move and upheaval at the house (carpet layers, painters,etc), that may have upset her, and this is not uncommon. We then made an appointment for her to come in the next morning for her yearly immunizations, feline leukemia, feline infectious peritonitis, and rabies. By early afternoon she was vomiting, several times. I talked to the vet office and they said to keep an eye on her, as she seemed fine in behavior otherwise. By mid/late afternoon she was vomiting blood. We took her to the vet and by this time she was frothing at the mouth. On the examining table she starting expelling blood rectally (more blood than mucous, here) and was extremely lethargic, couldn't lift her head. She was run to the back and they started an IV, giving her 280cc Ringers and 8 mg Decadron (7 1/4 lb. cat). I saw her an hour later and she was just as sassy as could be, and has been since, 3 days later. My question is, is there one of these immunizations that could have caused this reaction (the vet didn't know which one) and is it necessary for her to have all these immunizations as a complete house cat. I think some of these diseases are caused by mosquito, and so may be more necessary due to our South Carolina climate. However, I am afraid that the treatment is worse than the disease. What do you recommend for the future?


A: Elizabeth-

The reaction that you saw in Christine is atypical of vaccine reactions, at least based on the ones we have seen, but it still seems most logical that a vaccine reaction occurred, especially with the response to dexamethasone therapy.

It is hard to tell you which vaccine may have caused the reaction but I think that it is generally accepted that chlamydiosis vaccination causes the most reactions. The "yearly" vaccine used at some veterinary hospitals includes this component and at others it is not included. Feline leukemia vaccination and rabies vaccination probably are about equal in their potential to cause reactions and it is my impression that they are the next most common causes of vaccine reactions. FIP vaccine is supposed to have a low potential for immediate reactions but has other safety questions concerning its use. Rhinotracheitis and calicivirus vaccinations can cause reactions and these can be more severe in a kitten or cat harboring one of these diseases at the time of vaccination. Panleukopenia vaccine probably is involved in some of the reactions.

So what do I recommend for a cat that has had a reaction to vaccination?

First, evaluate the risk of these illnesses for your cat. Feline leukemia virus needs direct contact to spread to another cat. FIP is not very common in single cat households and neither are the other viral illnesses, for that matter. Cats that are interacting with other cats are more susceptible to all of these conditions and situations in which cats and kittens mingle seem to be the most ripe for viral shedding. Rabies vaccination is required by law in most states.

Christine probably fits in the "low risk" category for all of the feline viral illnesses.

Adult cats are highly resistant to feline leukemia virus, in most cases. We do not recommend feline leukemia vaccination for indoor only cats. So it would be easy for me to eliminate this potential cause.

Feline infectious peritonitis virus vaccination does not appear to be highly efficacious, to me, and there is some evidence to suggest that vaccine induced FIP infections have occurred, rarely. Indoor only cats are not likely to be infected. We have not used this vaccine in our practice for several years.

We do not use chlamydiosis vaccine.

These three vaccinations would be easy choices for elimination, in my opinion.

We use an every three year schedule for the remainder of the vaccinations you mention, in our practice. It may be smarter, in Christine's case, to spread the vaccines out and give them separately, so that you can figure out which one is causing problems. You might try a schedule in which you give the rhinotracheitis and calicivirus vaccinations next year or the year after (as far as I know, these two viruses only come combined) and then give the rabies vaccination on schedule. Panleukopenia vaccine can then be boostered another year. Plan on spending some time at the vet's after the vaccinations. Once you have the vaccines on a rotating schedule, you could go to every three year vaccination. This would allow monitoring of which vaccine caused problems and then it would be possible to even further refine the "risk vs. benefit" decision. If the culprit is panleukopenia, for instance, it is likely to be safe to skip it since the immunity from this vaccination is long term -- perhaps even lifelong.

You do have to consider the possibility that this was a coincidental event. Keep an eye out for recurrences of blood in the stool. A surprising number of apparently normal cats have occasional blood in the stool -- but it is still worth a few checkups and some lab tests to be certain of this if it recurs. Especially since you know she can have very bad symptoms, sometimes.

I am not sure if it is the only possible illness with a mosquito vector, but heartworm disease is the only one that I can think of, off the top of my head. There are heartworm preventatives for cats and surprisingly, this disease does seem to occur occasionally in indoor cats, presumably due to a mosquito species that can carry the heartworm microfilaria and likes the indoor environment. Heartworm prevention medications are available for cats.

Hope this helps.

Mike Richards, DVM 8/7/99

Feleuk vaccine risk

At 02:20 PM 9/9/97 -0700, you wrote: You refer to possible risks to giving a cat a feline leukimia vaccination. What are the risks? I have two cats, both strictly indoor. Toby is 7 and Tiger Lily is 1. My vet has recommended feline leukimia vaccinations -- his rationale is that if they should have to be hospitalized for some reason, they may pick up leukimia from another cat who is in the hospital. Is the likely? Many thanks for your reply.

A: sengv- The biggest risk associated with vaccination with feline leukemia virus is a potential increase in the likelihood of fibrosarcoma, a form of cancer, at the injection site. While there is still some debate about the link between vaccination and formation of this cancer I tend to think we should be cautious in use of vaccinations until the issue is sorted out. Other risks include anaphylactic shock (very rare) due to sensitivity to the injection and immune suppression for a short period of time post-vaccination.

These risks have to be weighed against the risks of not vaccinating for this disease. Feline leukemia is transmitted by direct contact with another cat. It is not an airborne infection and the virus can only live outside the cat's body for a very short time, literally seconds. Therefore, an indoor cat has very little chance of being exposed to the virus. Sometimes an indoor cat escapes from home. Unvaccinated and without natural exposure experience, this cat would be more susceptible to getting feline leukemia if it did have contact with an infected cat. I can't think of a good excuse for a cat in my hospital to be exposed to this virus during its stay. I do not allow contact between my hospitalized patients and transmittal by my staff is not at all likely since the virus is so susceptible to death in the environment. In our hospital the biggest risk in is the exam room prior to a visit when a client may allow their cat to wander before we notice. If you bring your cats in a carrier, which you always should do, there is almost no risk in this situation, either.

My personal opinion remains that in the case of feline leukemia, the risk of vaccination outweighs the risk of not vaccinating in a truly indoor cat. I feel just as strongly that indoor/outdoor and all outdoor cats should be vaccinated, since the risk of contacting the disease is so much higher for them. Your vet's opinion is obviously different and he or she may have experiences or other knowledge that causes them to see this situation differently.

Hope this helps.

Mike Richards, DVM

Lump - reaction to vaccination

Q: Yesterday while brushing Dewberry I noticed a lump about the size of a marble behind his front right leg. It didn't seem to cause him any discomfort when I touched it other than I was disturbing his brushing time. Could this lump be a reaction or the result of his recent shots?

A: The lump is very likely to be a reaction to the vaccination. If you remember it being given in that particular area, it is even more likely. Vaccination reaction lumps are usually non-painful and do not feel hot. If this is not the case, please contact your vet now. In any case, you should mention this to your vet so it gets put in the records -- once in a very great while, there are serious complications to vaccine reactions, including skin cancer at the vaccination site.This is not a good reason not to vaccinate but it is a good reason to make sure all reactions are noted

Mike Richards, DVM

Vaccine induced fibrosarcomas

Q: Thank you for your web page on vaccine induced fibrosarcomas. I just lost my cat yesterday from a recurrence of vaccine induced sarcoma. What can I do to help prevent these sarcomas?

A: There are several things that might help to prevent vaccine induced fibrosarcomas.

The first consideration is when and how to vaccinate. I think that veterinarians need to consider the risk to their patients of vaccination and then consider how likely a cat is to be exposed to the diseases being vaccinated for. When risk of disease is very low, such as for a solitary housecat, it may be a good idea to consider vaccinating every three years instead of yearly. If a cat has a need for yearly vaccinations, such as an outdoor only cat, then it may be a good idea to consider vaccinating low on a limb so that if a fibrosarcoma does occur the limb may be amputated to prevent its spread. Personally, I haven't started vaccinating in this manner because I am not sure that my clients would be willing to accept amputation in many instances. Therefore, we stick to the flanks and hope to be able to remove enough area around any tumors that occur to limit their spread. I am still thinking about how to deal with this issue -- so my ideas may change.

The next consideration is what to vaccinate with. Modified live virus vaccinations or recombinant vaccinations that do not contain an adjuvent appear to be the safest choices at this time. It is likely that recombinant technology vaccinations will be available for almost all diseases we vaccinate for within the next few years.

This is a tough issue. It has certainly changed the way we think about vaccination of cats.

Mike Richards, DVM

Not eating after vaccination

Q: Our 4 year old cat had shots booster shots about a month ago. He began to lose his appetite after the shot and has lost about 2 pounds. Percy only weighs about 7 pounds now. Took him to the vet. Vet put him on Cefa Drops about 1 1/2 units twice a day. We have given the cat I.V. therapy of twice a day to replace liquids and tried feeding him this paste on his palate - smells like beef buillion- has lots of nutrients in it, but he does not really like it. fights having it. Cats heart rate is up- do not know whether it is from not eating or what - have done blood tests nothing alarming no leukemia . Vet is going to pull liquids from the lung area and have it tested today. Looking for heart failure- thickening of the heart muscles so on. cat drinks water and is mainting litter box habits. Any thoughts? B.

A: I always worry when a cat is not eating, whatever the cause. We have seen severe illness coincidentally with vaccination on several occasions in our practice. Since we see illnesses on a random basis it makes sense that sometimes they will occur at the same time as vaccines. It is also possible that the immunosuppression that occurs for a short period of time after vaccination may give an illness a temporary "boost" in its ability to cause problems. In some cats and dogs reactions to vaccination probably do occur and may be severe. Most of these reactions are either immediate (anaphylactic shock) or are delayed about 5 to 7 days after vaccination (delayed hypersensitivity reactions). It is very difficult to figure out if a problem is an illness or vaccine reaction in the delayed response reactions. Supportive care is usually all that is required for these reactions, such as the fluids and nutritional supplement your vet is using. It is important to continue to try to rule out other possible problems -- since these are more likely than vaccine reactions. It is worrisome if there is fluid accumulation in your cat's chest and the not eating is worrisome, as well. Please continue to work closely with your vet to get to the bottom of this problem. If necessary, ask your vet about referral to an internal medicine specialist for a second opinion. Sometimes it is helpful to let a specialist look at a pet with a difficult problem, since their caseload tends to be all the unusual things that other vets don't see as often.

Good luck with this. Mike Richards, DVM

Rabies Vaccine lump

Q: I 'm worried about my cat. Several weeks after her rabies booster, she developed a lump at the injection site. My vet said it was probably benign but he should recheck in a month. He also said some cats get malignant tumors at the injection site after about a year, but its rare.

A: A lot of cats get a lump following rabies vaccination. A very small percentage of cats do develop malignant tumors from rabies vaccination. If the lump persists for more than one month it should be removed and a good deal of skin around it removed as well. The lump should then be sent in for examination to determine if it was a tumor. There is no point in worrying right now -- minor reactions are much more likely. Mike Richards, DVM

Lump from Vaccination?

Q: Yesterday while brushing Dewberry I noticed a lump about the size of a marble behind his front right leg. It didn't seem to cause him any discomfort when I touched it other than I was disturbing his brushing time. Could this lump be a reaction or the result of his recent shots?

A: The lump is very likely to be a reaction to the vaccination. If you remember it being given in that particular area, it is even more likely. Vaccination reaction lumps are usually non-painful and do not feel hot. If this is not the case, please contact your vet now. In any case, you should mention this to your vet so it gets put in the records -- once in a very great while, there are serious complications to vaccine reactions, including skin cancer at the vaccination site. This is not a good reason not to vaccinate but it is a good reason to make sure all reactions are noted. Mike Richards, DVM

Last edited 08/30/04


Michael Richards, D.V.M. co-owns a small animal general veterinary practice in rural tidewater Virginia. Dr. Richards graduated from Iowa State University's College of Veterinary Medicine in 1979, and has been in private practice ever since. Dr. Richards has been the director of the PetCare Forum...