30 March 2015

Cats: Adverse Reactions to Vaccines

One of the major objections to vaccines by many people who do not vaccinate their cats has to do with reactions to the vaccines.  I know from personal experience with my cats that most cats have little reaction to vaccines, but for others, the reactions can linger for 3-5 days, cause vomiting, and cause stiffness.  I have also heard of much stronger reactions, to the point of death.  (I also acknowledge that some of the reactions may be overstated by upset owners, but still....)

This article, Vaccine-Associated Adverse Events, by E. Kathryn Meyer, VDM (p 493-514 in Vol 31, No 3, Vet. Cl. of NA: Small Animal Practice, May 2001) was interesting for several reasons.  First because it explained how the reactions are noted in the licensing of vaccines.  And second because of the range of reactions which the author admits to.  This latter is especially interesting because in personal conversations with various vets, I have been clearly told that there are none or almost no reactions to vaccines.

General Background on How Vaccine Reactions are Studied
Prelicense Studies:  These are trials conducted by the vaccine manufacturer, involving a small number of animals.  With cats and Chlamydia for example, there are 20 vaccinated cats and 10 control cats.  To get a label claiming prevention, the vaccine must be 80% effective.  Each vaccine batch must be in vitro tested for potency. 

The duration of immunity (DOI) determines the revaccination interval, but DOI studies are not required to support vaccine label recommendations for boosters.  This seems a bit inconsistent to recommend boosters without any evidence that boosters are needed.

The safety of a vaccine is determined by a larger field trial, which may or may not capture adverse reactions which are rare.  If there are adverse reactions observed, these are NOT required by law to be on the vaccine label.

Postlicense Studies:  “systematic monitoring of canine and feline infectious disease, with the exception of rabies, is not routinely performed”.  So, in essence, one cannot say that statistically the use of the herpes vaccine has decreased the incidence of the disease, although common observation would say it does. 
Reactions after licensing also do not have to appear on the vaccine label (except in certain specific cases with dog vaccines) and manufacturers are leery of doing so because it creates the image that their vaccine is unsafe.  The postmarketing surveillance is mainly by passive systems in that the vet contacts both the manufacturer and the USDA, but the few vets do this and in most cases (97%) they will report problems only to the manufacturer.  In 2001, the USDA Center for Veterinary Medicine was going to publish a rule requiring industry reporting of adverse reactions.  It does not seem this rule was ever published because (a) I could find no reference to this rule in vaccine discussions after 2001 and (b) as late as last year, reporting of vaccine reactions still was on a voluntary basis by the individual vet.

Adverse Reactions
Systemic Reactions: Nonspecific Systemic Reactions
This is anorexia, lethargy, fever, and soreness from 1-36 hrs after inoculation.  Most cases are mild, but a few are severe, and are presumed to be an immune response to the vaccine.  In a clinical study, the rate was 1.2% with cats older than 1 year and cats receiving multiple vaccines at greater risk.  The implications of this seem to be that a previous vaccination as a kitten may very well prime the immune system to react to the vaccine.  Also, this seems to be in alignment with many holistic vets' recommendation not to give multiple vaccines at one time.  For example, vaccinate for FeLV one month and rabies the next month, instead of all at once.

Systemic Reactions: Anaphylaxis
This is a reaction involving the lymph system (IgE mediated) involving the skin, intestines, and lungs.  The reaction can last up to 48 hrs and may require steroids, antihistamines or epinephrine.  In a study, 0.26% of cats had an anaylaxic reaction with 66% of those involving the intestinal tract, 22% respiratory, and 12% skin.

Systemic Reactions: Autoimmune Disease
Interesting, there are no reports of vaccines triggering an autoimmune disease in cats, only in dogs.  The time frame was 2-14 days and involved problems like hemolytic anemia.  My personal, non-vet opinion, is that some of the autoimmune diseases, such as IBD, are actually triggered by over-vaccination, but as the author clearly stated, there is no evidence for this view.  Then again, proving causation between a vaccine and a long-term immune problem would be difficult at best.

Systemic Reactions:  Immunosuppression
One study showed that some kittens vaccinated with an intranasal modified live panleukemia vaccine became immunosuppressed which lead to a systematic infection by Salmonella. When I think about this, this is not surprising since a vaccine works by challenging the immune system.  If the immune system is working to fight off panleuk then other bacteria and viruses can easily be overlooked by the immune system.

Systemic Reactions:  Vaccine Virulence
Modified-live vaccines (MLV) can cause reactions similar to the disease.  Calici and herpes MLV are well known to cause sneezing and sniffles 4-9 days after proper vaccination.  Calici MLV can cause ‘limping calici’.  With pregnant cats, MLV can cause fetal abortion or developmental problems. There are reports of MLV for rabies not being inactivated enough that it actually causes rabies.

Systemic Reactions: Product Contamination
Each batch of vaccine is tested for other viruses, fungi, mycoplasma, and bacteria.  Vaccine contamination still does occur and when it does, it affects a large number of animals.  But there are no specific statistics on how wide-spread the problem is.

Local Vaccine Reactions:  Pain
In cats, lameness lasting for a few days to several weeks is not uncommon since vets are now vaccinating in the hind limbs.  The lameness is from an inflammatory response.

Local Vaccine Reactions:  Benign Swellings
These swellings are not considered an adverse reaction by many vets, but the normal reaction.  Rabies vaccines in cats accounted for 72% of reported ‘benign vaccine lumps’.  In a small study of 9 cats, all cats developed them after rabies, only 1 after FVRCP, and none after FeLV.

Local Vaccine Reactions:  Injection Site Sarcomas
This was a topic of a separate article and will be dealt with there.

Local Vaccine Reactions:  Vaccine Site Alopecia
Most reports of hairloss at the injection site are related to rabies vaccine.

Local Vaccine Reactions:  Abscesses
With cats, the reports were linked to ringworm vaccinations.  As a side-note, the ringworm vaccine was never common and now seems to be unavailable in the US.

Local Vaccine Reactions:  Intranasals
Problems involving the FVRCP vaccine include nasal ulcers, oral ulcers, and eye ulcers.

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