Vaccines for Cats: We Need to Stop Overvaccinating by Lisa A. Pierson, DVM

June 26, 2012

Thanks to Lisa A. Pierson, DVM for allowing us to post her wonderfully informative article on cat vaccination from her website which also includes information on feline nutrition, health and rescue:  This article contains:

General suggestions
Side effects including sarcomas (cancerous tumors), chronic kidney disease, allergic or anaphylactic reaction, vomiting, diarrhea, lethargy, soreness at the injection site, lameness
Vaccine types
Decision-making criteria – including comments on titers


A vaccination is a preparation of microorganisms (pathogens), such as viruses or bacteria, that is administered to produce or increase immunity to a particular disease.  There can be no disputing that vaccines save lives but they also have some serious side effects which will be discussed on this webpage.

Please note that the diseases we most commonly vaccinate cats for are caused by viruses – not bacteria.  While it is difficult to induce long-term immunity to bacterial infections, vaccines targeted toward viruses are much more efficient at conferring long-term immunity in the recipient.

There are 5 viral diseases that cats are commonly vaccinated for:

  • herpes (rhinotracheitis) – the ‘R’ in FVRCP

  • calici – the ‘C’ in FVRCP

  • panleukopenia (“feline distemper”) – the ‘P’ in FVRCP

  • feline leukemia – FeLV

  • rabies

Please DO NOT vaccinate for FIV (Feline Immunodeficiency Virus – aka “feline AIDS”), FIP (Feline Infectious Peritonitis), bordatella, giardia, or chlamydia.

The subject of vaccine administration is one of the most controversial topics in human and veterinary medical literature, making it a common area of debate – and stressful decision-making – among parents and pet owners.

Given that this is an area of controversy, I want to start with a ‘food for thought’ question:

How often are you getting vaccinated for measles, mumps, chicken pox, tetanus, etc.?  Yearly?  Every 3 years?

I doubt it. 

So why aren’t more people questioning the reminder cards that veterinarians send out asking for the pet to be brought in for yearly vaccines? 

Taking it one step further, why aren’t more questions being asked about the ‘newer’ suggestions to vaccinate cats for FVRCP, and in some cases, FeLV, every 3 years – given that we have plenty of data to show that it is not necessary to vaccinate cats for these diseases even this frequently?

A cat’s immune system is not any more ‘forgetful’ than a human’s immune system.  In other words, there is no reason to believe that they need to be vaccinated so often.  Their immune system, to the contrary, has a very good memory.

For many years, humans have thought of vaccines as ‘all good and no bad’ but that line of thought cannot be further from the truth.  Given the serious side effects that can manifest themselves after a vaccine has been given, people need to start applying more critical thought – including a risk-benefit analysis – when making decisions about vaccination protocols.

It is very important to understand that no vaccine is 100% safe. 

However, it is also very important to understand that vaccines save lives and there can be no debating that fact.

These two facts, along with other factors discussed on this page, enter into every decision we make regarding how we vaccinate our cats.

I wish that I felt comfortable saying “ask your veterinarian for the best advice regarding the vaccination of your cats” but I don’t. 

Unfortunately, many of my colleagues are simply not taking the time to carefully peruse the scientific literature that provides ‘duration of immunity’ (DOI) data showing that we are over-vaccinating many of our pets – even with the 3-year protocols in the case of FVRCP and FeLV.  (Rabies will be discussed separately.) 

This webpage is not intended to be a comprehensive discussion on all matters involving vaccinations but, instead, will cover some vaccine basics, current (2010)  WSAVA-VGG (World Small Animal Veterinary Association – Vaccine Guideline Group) suggestions, current (2007)  AAFP (American Association of Feline Practitioners) suggestions, and my personal views on the subject – including how I vaccinate my own cats.

Please note that even some (all?) of the experts who sat on the panel that came up with the AAFP suggestions, as well as one veterinarian who is head of the vaccine division of a major vaccine-producing company, do not vaccinate their own animals as frequently as their guidelines/suggestions/package label states. (source:  personal communication) 

These veterinarians acknowledge that the current suggestions/package labels do not reflect the fact that challenge studies have shown a very long duration of immunity (DOI) – lifelong, for some diseases – from just a single, properly-timed, vaccine. 

Unfortunately, it has been hard enough to get veterinarians to switch from annual vaccines to the current 3-year protocol so it is going to be an uphill battle to get them to vaccinate even less frequently.  Therefore, I do not see changes in the AAFP suggestions coming anytime soon.

To put this in perspective, note that the recommendation to go to a 3-year vaccine protocol came out of Colorado State University more than 15 years ago, yet there are still many veterinarians administering annual vaccines.

This reluctance to change is especially true of the older generation veterinarians (myself included having been involved in this profession for over 30 years) who lived through a time when the mortality rate from rabies, distemper, etc., was very high.  Vaccines came along and saved lives – no question – but it is time to start paying more attention to the current DOI studies – some of which have been available for many years.

I urge the reader to take the time to do their own research into this area and not necessarily rely only on your veterinarian’s recommendations.  It will be up to the reader to decide how they want to handle vaccine administration in their own kittens and adult cats for FVRCP and FeLV.

My goals in writing this page are to get the reader to:

  • stop blindly over-vaccinating their cats

  • apply more critical thought – including reading the studies


Yes, I am shouting about the last issue.  There is no good reason for any veterinarian to inject an adjuvanted vaccine into any feline patient.

Adjuvants are substances that are added to vaccines to purposely cause inflammation at the vaccine site in order to alert the immune system to its presence.  They are used with killed vaccines to stimulate a more robust immune response but can also cause fatal, aggressive tumors at the site of vaccine injection.  (See below for a picture of “Chicken” – a sweet cat who is battling this cancer.)

DO NOT assume that your vet is using the safer, non-adjuvanted vaccines.  ASK before allowing any vaccine to be administered to your cat.

To repeat much of what I have said above:  There is nothing in the scientific literature to support annual vaccination with the FVRCP and Feline Leukemia (FeLV) vaccines.  It is well-known that:

  • the vaccines commonly used for cats confer immunity for much longer than 1 year – and actually provide lifelong immunity in most instances for panleukopenia

  • adjuvants contained in killed vaccines put cats at risk for fatal tumors (sarcomas)

  • even the non-adjuvanted FVRCP vaccines have caused sarcomas, as have the PureVax vaccines

  • natural immunity to feline leukemia is very strong by the time the cat reaches ~1 year of age

  • the FVRCP vaccine is strongly linked to kidney inflammation

Please note that kidney disease is the most common subject that I consult on and it is considered by many to be the number one cause – or at least a very common cause – of death in our older cats. 

General Vaccine Suggestions

(Please note that I cannot offer individual vaccine advice outside of a to discuss the details of your situation.)

At the end of this webpage, please see:  Age and Long-term Protective Immunity in Dogs and Cats and Membranoproliferative glomerulonephritis possibly associated with over-vaccination in a cocker spaniel.


Keep in mind that a vaccine protocol is not a ‘one size fits all’ issue and that the medical community is lacking in definitive research in many areas of vaccinology.  This is why the WSAVA-VGG, the AAFP, and myself make suggestions regarding vaccine protocols – versus etched-in-stone statements.  

To repeat, there are 5 viral diseases that cats are commonly vaccinated for:

  • herpes (rhinotracheitis) – the ‘R’ in FVRCP

  • calici – the ‘C’ in FVRCP

  • panleukopenia (“feline distemper”) – the ‘P’ in FVRCP

  • feline leukemia – FeLV

  • rabies

Please DO NOT vaccinate for FIV (Feline Immunodeficiency Virus – aka “feline AIDS”), FIP (Feline Infectious Peritonitis), bordatella, giardia, or chlamydia.

Keep in mind that if you do decide to vaccinate for FIV (a very ineffective and adjuvanted vaccine), your cat will now test ‘positive’ since the FIV test cannot tell the difference between an infected cat and a vaccinated cat. 


Most people are familiar with the abbreviation ‘FVRCP‘ which stands for Feline Viral Rhinotracheitis (herpes), Calici, Panleukopenia.  FVRCP is a combination vaccine that includes 3 out of the 5 vaccines that will be discussed on this webpage.

This vaccine can either be modified live (NON-adjuvanted) or killed (adjuvanted).  The route of delivery can be either injectable or intranasal.

Only use a modified live (NON-adjuvanted) – never a killed (adjuvanted) – FVRCP vaccine, with injectable (not intranasal) being the preferred route of administration in most, but not all, instances.

To clarify – all modified live vaccines (MLV) are NON-adjuvanted.

Herpes and calici:  These are the upper respiratory viruses that can cause watery/swollen/ulcerated eyes (mainly herpes), sneezing, nasal congestion, and oral ulcerations.  The severity of illness ranges from very mild to severe but the mortality rate is very low. 

Unfortunately, as is true for the ‘common cold’ in humans, there is no 100% effective vaccine for herpes and calici in the cat.  One reason is that these viruses mutate (change) frequently and there are many different strains.  The vaccine will not prevent infection but will, hopefully, lessen the severity of clinical signs. 

Panleukopenia:  This is a highly contagious virus that infects the intestines causing severe bloody diarrhea and vomiting.  This disease has a very high mortality rate.

Do not let your kitten go unprotected from panleukopenia.  This virus can cause a very cruel death.

My suggestions:


Vaccinate kittens with FVRCP twice starting at 8-9 weeks of age with the second, and final kitten vaccine, administered when the kitten is no younger than 16 weeks of age.

The AAFP guidelines state that you can start this vaccine when the kitten is as young as 6 weeks of age but, unless there is a very high index of risk, I would definitely not vaccinate a kitten this young.

We wait until the kitten is at least 16 weeks old to receive his last kitten shot because the antibodies he got from nursing on his mother will have decreased to a low enough level that his own body can respond to the vaccine in order to make his own antibodies.  (Maternal antibodies within the kitten can ‘tie up’ the vaccine before his body has a chance to respond to it.)

The AAFP and WSAVA-VGG guidelines suggest giving the FVRCP every 3-4 weeks until the kitten is 16 weeks of age.  This is to try to vaccinate the kitten the minute his maternal antibody level wanes to a low enough level to allow him to respond to the vaccine.  That way, there will be a minimal gap between the time his mother’s antibodies stop protecting him and the time when he can start making his own antibodies.

That said, I would rather not give this many vaccines to a kitten.  Unless there is a high index of risk, I prefer to limit it to 2 vaccines total for the kitten series.

If you read the AAFP guidelines, there is the potential for administering 4 vaccines in the kitten series.  Given the fact that the FVRCP vaccine has been proven to cause kidney inflammation, I am not comfortable following their suggestions.

See Membranoproliferative glomerulonephritis possibly associated with over-vaccination in a cocker spaniel puppy at the bottom of this webpage.

The above case involved an owner who, without veterinary supervision, vaccinated his puppy 7 times – 1 time per  month.  The puppy died at 7 months of age from kidney failure due to kidney inflammation.  The two most striking facts/comments in this case report are:

“In addition, antigens in the complexes were similar to the vaccine antigens in the DHLPP vaccine, suggesting that the glomerulonephropathy in this puppy was secondary to frequent and unnecessary vaccination.”


Further studies are required at this time to determine the role, if any, that recent past and current vaccine protocols play in the development of protein-losing nephropathies.”

The last statement is very important considering the fact that chronic kidney disease is the most common subject that I consult on and that 2/3 of the kidney cells must be non-functioning before we see any elevation in blood markers such as BUN and creatinine.  Therefore, we certainly may be damaging kitten kidneys by giving them 4 vaccines by the time they are 4 months old but not be aware of it.

Put another way – if 7 vaccines in 7 months resulted in the death of a puppy, then I am not comfortable with 4 vaccines within 10 weeks for a kitten.

Young adults:

The AAFP and WSAVA-VGG guidelines suggest giving a booster FVRCP 1 year after the last kitten vaccine – i.e. – when the cat is ~ 16 months of age.  However, if the kitten responds as he should to the kitten series, this booster should not be needed.  The rationale behind the 1 year booster shot is to cover any kitten that did not properly respond to the kitten series.

Reasons why a kitten may not fully respond to a series of vaccines as a kitten and would benefit from a 1 year booster are:

1)  The last kitten shot was given when he was younger than 16 weeks of age. 

2)  Maternal antibodies hung on longer than 16 weeks and interfered with his immune system’s ability to respond to the last vaccine.  (We have good studies showing that the maternal antibody levels are low enough in most kittens to allow them to respond to a vaccine by the time they are 8-12 weeks of age so this is an improbable scenario.)

3) The kitten was in poor health when vaccinated and did not respond properly.  (Vaccines should never be administered to sick animals but, unfortunately, unhealthy animals are vaccinated more often than you may think.)

4) The vaccine was of inadequate immunogenicity which means that the vaccine was damaged in terms of its efficacy. This could happen due to a problem within the manufacturing process or because of poor handling of the vaccine after it left the manufacturing plant.

Note that some cats are genetically ‘non-responders’ and never will respond to a vaccine no matter how many you give them.  In these rare cases, giving a booster vaccine 1 year after the last kitten vaccine would be of no benefit.

Deciding to give a booster vaccine 1 year after the last kitten vaccine, or not, is a judgment call. 

The older a kitten is (past 16 weeks of age) when he receives his last kitten shot, the less inclined I would be to give a booster shot 1 year later.

This is because the older he is, the more mature his immune system is – and better able to respond – and the less chance there will be for the maternal antibodies to be at a high enough level to interfere with his ability to respond to a vaccine.

Another option would be to test his titer (antibody level) to panleukopenia (not herpes or calici) to help you make a decision.  (More on titer testing below.)  This is what I would personally opt for.


I do not repeat the FVRCP vaccine past the kitten shots – or past the 1-year booster as discussed above. 

We must stop vaccinating with FVRCP every year. 

Taking it one step further, I also disagree with the AAFP guidelines which suggest giving the FVRCP every 3 years since the risks outweigh the benefits.


Consider the facts that enter into the risk-benefit analysis

1) A single, properly-timed, FVRCP vaccine confers life-long immunity to  panleukopenia (the most serious disease among the 3 that the FVRCP targets) in the vast majority of cats.  Those very few cats that may not be protected are considered to be ‘non-responders’ and giving them more vaccines is unlikely to help.

2)  Herpes and calici vaccines lack the ability to induce complete protection. At best, they will only reduce the severity of some symptoms but will not prevent infection with these viruses and will not protect the recipient from all symptoms of disease.

3)  Herpes and calici viral infections do not have a high mortality rate.  Death from these viruses is extremely rare and, if it did occur, it would most likely happen in kittenhood.

4) Even though a non-adjuvanted FVRCP vaccine is much less likely to cause a sarcoma, sarcomas have been noted with these vaccines.

5) And most importantly, as noted below, there is a strong link between chronic kidney disease and the FVRCP vaccine.

My own cats are over 10 years of age and have not been vaccinated with FVRCP since their properly-timed kitten series.

If you rescue/adopt an altered (spayed/neutered) adult with an unknown vaccine history, I strongly suggest running a titer for panleukopenia rather than vaccinating blindly.  If the cat is spayed or neutered, chances are she or he was vaccinated as a kitten.  However, the age at which he received his last kitten vaccine (past 16 weeks of age?) will not be known so the decision to administer a vaccine, or not, is a judgment call.  This is a situation where titer testing can help out. 

As odd as it may sound, if I rescue a neutered adult male cat with a fairly good size (empty) scrotal sac, I assume (rightly or wrongly….) that he was most likely not neutered before the age of 16 weeks.  (Male cats that are neutered very young have a very flat scrotal sac.)  Given that most cats are vaccinated when they are neutered, this gives us a hint (and nothing more than that) that the cat may very well have received a vaccine past the age of 16 weeks. 

Also, keep in mind that many of these stray cats have been ‘travelling the streets’ and may have a good dose of natural immunity to some feline diseases although that cannot be counted on definitively.

The AAFP guidelines call for a series of 2 FVRCP vaccines to be given 3-4 weeks apart to an adult with an unknown vaccination history but the WSAVA-VGG recommends that only 1 FVRCP vaccine be given with a booster vaccine 1 year later.

In lieu of this 1 year booster, I would suggest titer testing.

Studies have shown that cats over 16 weeks of age with a healthy immune system respond very well to just 1 FVRCP vaccine. 

Feline Leukemia (FeLV):

Feline leukemia, that results from the feline leukemia virus, is a complicated disease.  It typically attacks the bone marrow of the cat but cats vary in their response to the virus.  Some cats clear the virus from their system and become FeLV ‘negative’, some cats live for many years with the virus in their body but are not symptomatic, and some cats become ill and die within a few years of becoming infected.

FeLV is NOT highly contagious and its transmission requires prolonged contact with an infected cat. Natural immunity is very strong in most cats by the age of 1 year.  AAFP guidelines suggest vaccinating all kittens but the vaccine is recommended in adults only if they will be in contact with a known FeLV positive cat – which would be a very rare situation.

I disagree with the recommendation to vaccinate all kittens. None of my own cats have ever been vaccinated for FeLV – not even as kittens – since they reside indoors and will not be in contact with a FeLV positive cat.

My suggestions:

Do not vaccinate kittens for FeLV unless your kitten is going to be outside (rarely a safe place to be for any kitten or cat) or is going to be housed with an FeLV positive kitten or cat. 

Do not vaccinate adult cats for FeLV – even if they have access to the outdoors – since natural immunity to this disease is very strong by the time the cat is ~1 year of age.  If an adult cat is going to be living with a FeLV positive cat, then vaccination should be considered.

If you do choose to vaccinate for FeLV, ONLY use the Meriel PureVax FeLV vaccine which is NON-adjuvanted.  All other FeLV vaccines are killed and contain adjuvants which should never be injected into any cat.


This is a very serious disease with 100% mortality in animals and humans.  (There is only 1 known human survivor and I don’t know of any animal survivors.)  Since humans can contract rabies from animals, including cats, vaccinating cats for rabies is required by law in some areas of the country.

Any cat that is exposed to the outdoors, or any indoor cat that could possibly come in contact with a bat, should be vaccinated for rabies.

Bat rabies is the most common strain to infect humans.  Bats can live in attics, fly down chimneys, come in through windows, and ‘indoor-only’ cats have been exposed to rabid bats on balconies.

There is only one suitable rabies vaccine and that is Merial’s PureVax rabies vaccine.  This is a NON-adjuvanted vaccine.


Unfortunately, the PureVax rabies vaccine only carries a 1-year rating even though 2 studies have shown that it protects cats for much longer.  This is in contrast to the more dangerous adjuvanted rabies vaccines that carry a 3-year rating.

Merial conducted 2 well-run studies showing that their PureVax rabies vaccine protected all study participants from a challenge with the rabies virus 3 years later.  However 1 ‘control’ (non-vaccinated) cat in each study did not die from the rabies challenge. Therefore, Meriel was not granted a 3-year license for this vaccine.  Good science shows that this vaccine is protective for at least 3 years but legally, it is only labeled for 1 year protection.

Because rabies is such a serious disease and is transmissible to humans, the laws are very strict in this area.  If your cat bites someone and it has been longer than 1 year since receiving a PureVax vaccine, legally he is considered to be ‘not current’ on his vaccines and he may have to go into a quarantined environment for 10 days.  This is often done in a veterinary clinic but, occasionally, the cat is allowed to spend the time in his own home.

If your cat is not vaccinated at all and he comes in direct contact with a wild animal that is not available for rabies testing, quarantine for up to 6 months may be required.  How strictly this is enforced varies from state to state.

As counter-intuitive as it may sound, it is much safer to administer a PureVax vaccine yearly than it is to inject an adjuvanted rabies vaccine every 3 years.

That said, I do not recommend yearly PureVax administration unless your local laws mandate rabies vaccinations for cats, or your cat is at risk for rabies infection, or your cat is an aggressive biter and you fear having to deal with a quarantine situation. 

My own cats are not vaccinated for rabies since I live in an area where rabies is not common, my cats have never been outside and never will step ‘paw’ outside, and I am confident that a bat cannot enter my home.  My cats are also not allowed out on a balcony due to ‘high rise syndrome’…ie…it is very common for cats to fall off of balconies resulting in death or severe injury.

If your cat has health issues and you live in an area where rabies vaccination for cats is mandatory, ask your vet for a health waiver.  Keep in mind that only healthy cats are to receive vaccines and it states as such on every bottle of every vaccine.

The PureVax literature states that you can administer 1 vaccine as early as 8 weeks of age, followed by a second vaccine 1 year later. 

Keep in mind that the older the kitten is when he is vaccinated, the more efficiently his immune system will be able to respond.  Therefore, I would always wait until the kitten is at least 16 weeks of age before receiving a PureVax rabies vaccine.  Of course, the kitten needs to be kept indoors at all times until he is properly vaccinated.

Please note that fatal sarcomas have developed secondary to the administration of the PureVax rabies vaccine so this vaccine is not without risk.  However, the chance of a tumor occurring from a PureVax vaccine is lower than it would be with an adjuvanted vaccine. 

Side Effects


These are highly invasive, aggressive/malignant cancerous tumors that are often fatal within months of appearing.  

They are most commonly associated with vaccine adjuvants but can also form at the site of any injection that causes local inflammation – including the non-adjuvanted, modified live FVRCP vaccines, the PureVax line of vaccines, and drugs like Program (for fleas), Droncit (for tapeworms), and Convenia (an injectable long-acting antibiotic that is being over-used and abused).

Adjuvants are substances that are added to vaccines to purposely cause inflammation at the vaccine site in order to alert the immune system to its presence.  They are used with killed vaccines to stimulate a more robust immune response.

Unfortunately, this inflammation can lead to sarcomas.

The discovery that vaccine adjuvants can cause sarcomas led to the acronym VAS (Vaccine Associated Sarcoma).  Some people have tried to change this to ISS (Injection Site Sarcoma) because sarcomas can form in response to anything that causes inflammation of the area under the skin but the bottom line is that sarcomas were rare prior to the advent of adjuvants. 

(That said, I am still very careful about injecting anything into a cat – given their tendency to develop cancer at the site of any inflammation – if there is a safer alternative.  See this article on Convenia.)

Sarcomas need to be aggressively treated – at great expense – if one is to try to save the patient’s life.

Unfortunately, the PureVax line of NON-adjuvanted vaccines are more expensive than the adjuvanted vaccines.  Therefore, most shelters and many veterinary clinics still use the more dangerous adjuvanted vaccines.

DO NOT assume that your veterinarian uses the safer vaccines.

ASK – before allowing any vaccine to be injected into your cat.   

“Chicken” is a special kitty that ended up with a VAS after an adjuvanted rabies shot was given in the scruff area.  In addition to aggressive surgery, she has had to go through radiation and chemotherapy treatments.  Please note that these are very aggressive tumors with ‘tentacles’ that run deep into the tissues. Therefore, it is almost impossible to remove the entire tumor.  Click here to follow Chicken’s blog.

Please note:  NO vaccine (adjuvanted or non-adjuvanted) is to be given in the scruff area under any circumstance. They are to be given as low in a limb as possible.  This is to allow for limb amputation if a VAS occurs.

In 1997, the AVMA (American Veterinary Medical Association) came out with the strong recommendation to never use the scruff area for vaccines.  Evidently, the veterinarian who administered Chicken’s adjuvanted rabies vaccine either did not take this recommendation seriously or was not keeping up on his continuing education.  In addition to using the wrong location, an adjuvanted rabies vaccine was used instead of PureVax and Chicken is paying a high price for these mistakes.

Chronic Kidney Disease (CKD)  

As already mentioned, this is the most common subject that I consult on and it is upsetting to see so many domestic cats end up dying from kidney disease when it is not that prevalent in wild cats.  Sure….I ‘get’ that cats in the wild do not live as long as our little furry buddies but I still cannot accept that natural aging is the only factor involved in this disease process. 

Why do so many cats end up in kidney failure?

The answer – or at least, part of the answer – may lie in the fact that we have been over-vaccinating cats for many years.

Here is an excerpt from Dr. Michael Lappin’s studies in this area: (See below for a ‘plain English’ summary.)

“The Center for Companion Animal Studies at Colorado State University has shown that cats vaccinated with FVRCP vaccines grown on Crandell-Rees Feline Kidney (CRFK) cell lines can develop antibodies to renal (kidney) proteins, and that cats hypersensitized to CRFK cell lysates can develop interstitial nephritis.

The immunodominant antigens to which antibodies are formed in these cats are α-enolase and Annexin A2, both of which are linked to autoimmunity and renal disease in humans.

Recently, we have shown that cats administered FVRCP vaccines parenterally (i.e. injectable) have higher levels of circulating antibodies to these antigens than do cats who were administered a FVRCP vaccine via intranasal administration.”

Now…in plain English:

The viruses used to make vaccines need to be grown in what is called a “cell culture”.  The cells used to make the FVRCP vaccine are feline (cat) kidney cells.

When these kidney cells are injected into the cat (along with the vaccine), his immune systems views them as foreign and makes antibodies against them.  Unfortunately, those antibodies don’t know the difference between the injected kidney cells and his own kidney tissue resulting in an autoimmuneattack’ on his own kidneys.  (‘Auto’ means ‘self”.)

Most people have heard of Lupus.  Lupus is a life-threatening autoimmune disease most commonly seen in humans.  So, in essence, the FVRCP vaccines stimulate a Lupus-like reaction in the recipient. 

Allergic/Anaphylactic reactions

An allergic reaction, in simplistic terms, it is an overreaction by the immune system to a foreign substance that enters the body. 

An anaphylactic reaction is a very severe allergic reaction that affects the entire body and is life-threatening – even if treated promptly.

The typical ‘shock’ organ of the cat is the lungs.  If the reaction is severe enough, the signs can include coughing, difficulty breathing, coughing up blood, collapse, and death.

Another ‘shock’ organ of the cat is the intestinal tract.  Cats can exhibit mild to severe vomiting and diarrhea – sometimes bloody.

Other serious reactions can involve blood vessels (vasculitis), red blood cells (Immune Mediated Hemolytic Anemia), platelets (Immune Mediated Thrombocytopenia), and any organ of the body.

‘Milder’ allergic reactions can cause a swollen face, swollen limbs, and itching.

Foreign substances that can cause allergic/anaphylactic reactions include all vaccines, all drugs, foods, etc.

Vomiting, diarrhea, lethargy, fever, anorexia, lameness, neurologic abnormalities, local swelling and soreness at vaccine site

All of these negative clinical signs can be seen secondary to the administration of vaccines. 

Vaccine Types

There are 4 main categories of vaccines:


Do not use.

All killed vaccines are adjuvanted and may cause malignant tumors. 

All FeLV vaccines, except for PureVax, are killed.

Some FVRCP vaccines are killed.

Killed vaccines do not stimulate the immune system as efficiently as modified live vaccines.

Modified live (MLV)

MLV stands for Modified Live Virus.  They are all NON-adjuvanted.  The viruses contained in these vaccines are not killed but are attenuated (blunted) so that they will replicate in the recipient but, hopefully, will not cause disease.  Most, but not all, FVRCP vaccines are modified live.

‘Reverting to virulence’ means that the virus contained in the vaccine is now infective enough to cause disease. This is a rare risk of using MLV vaccines.

Note:  In 1999, I was involved in a situation where several kittens in a group died from panleukopenia post vaccination with a MLV FVRCP vaccine.  The vaccine was from a leading vaccine manufacturing company and after speaking with their head veterinarian, it was determined that the vaccine may have reverted to virulence. 

This means that the vaccine could have caused the very disease we were trying to protect these kittens from.  Since MLV vaccines do carry this risk, I try to limit the kitten series to 2 MLV vaccines.

Intranasal (IN)

Intranasal vaccines are also modified live viruses and all are NON-adjuvanted.  They are administered via the nose and eyes.  I do not use them for several reasons.  The following comments pertain to the intranasal FVRCP vaccine – keeping in mind that the most important virus among the 3 that any FVRCP vaccine targets is panleukopenia:

1)  The route of infection for panleukopenia is oral, not via the respiratory tract.  Intranasal vaccines are better at conferring immunity for respiratory viruses and are less effective than an injectable MLV for stimulating immunity to panleukopenia.

2)  There are no DOI challenge studies for panleukopenia post-intranasal vaccination like there are for the MLV vaccines.

3)  Even though they may be more efficacious for the herpes and calici viruses, they often cause sneezing and watery eyes and the owner needs to be aware of this.  Our rescue group tried using these vaccines and it was a disaster because our kittens had to sit out from adoptions for about 2 weeks due to sneezing and watery eyes.

4) On a positive note, intranasal vaccines cannot cause a Vaccine Associated Sarcoma and they have been shown to cause NO kidney inflammation.  However, even in light of these ‘pluses’ I am not comfortable using them to protect kittens against panleukopenia.

5)  In some situations (catteries and shelters with a severe herpes/calici problem), the IN vaccine that contains only the herpes and calici viruses but not panleukopenia virus is of value since it stimulates a local mucosal (the lining of the respiratory tract) immunity very quickly and is not affected by maternal antibodies.  Therefore, it can be given to kittens younger than the traditional 8 weeks of age.


Merial’s PureVax rabies and feline leukemia vaccines are recombinant vaccines which means they contain only a portion of the genetic material of a pathogen (virus).  Therefore, reversion to virulence (able to cause disease) is impossible.

Although I have not seen any literature on the negative reaction rate, I am going to assume that the recombinant vaccines will be less apt to cause an anaphylactic reaction because they contain fewer potential allergens.

They also do not replicate in the recipient and there is no reason to believe that they cause kidney inflammation.

To clarify:  Merial makes a PureVax FVRCP vaccine but it is not a recombinant product.  It is a modified live vaccine just like other manufactures make.

Recombinant vaccines are the safest type available.  While they can cause sarcomas (in my reading I came across a reference to two cases), they are much less likely to do so when compared to a killed/adjuvanted vaccine.  

Decision-Making Criteria

(Some of this dialog is also stated in the above sections.)

What are some of the factors that influence our decisions regarding which vaccines to use and at what frequency?

I will say at the outset of this discussion that my indoor-only cats (all over 10 years of age) have not been vaccinated since they were 4-6 months of age.  They have never set their paws outside and never will – barring a catastrophic event.

My barn cat (13 years of age) received his last FVRCP vaccine at the age of 5 or 6 months and received a FeLV series at around 6 months of age (before we knew how dangerous adjuvants can be; PureVax was not around at that time), and is vaccinated with PureVax rabies vaccine approximately every 3-4 years.

Please note that I do not administer more FVRCP vaccines to my barn cat than I do to my indoor-only cats. This is because the panleukopenia immunity from the FVRCP vaccine lasts for life in the vast majority of cats and I do not feel that the minimal amount of protection the herpes and calici fraction may provide is worth the downsides of the vaccine.  Remember, it is all about risk-benefit analysis. 

Now, having confessed my cats’ minimal vaccine history, I will state that what is ‘right’ for me and my cats, may not be ‘right’ for you and your cat(s).

Issues to consider:

  • age of patient

  • risk of exposure to the disease in question

  • prevalence of the disease in the environment

  • consequence of the infection

  • overall health of the patient

  • vaccine efficacy

  • DOI studies (Duration of Immunity) for the vaccine

  • vaccine properties (adjuvanted/non-adjuvanted, etc.)

  • titer testing

  • owner’s comfort level

Let’s start with the last one – the owner’s comfort level

This certainly does not sound like a very scientific factor but it is an important issue to consider.  Given the fact that all foreign substances do have side effects when introduced into any living being, I would be a hypocrite if I did not mention the owner’s feelings since my own comfort level is tested anytime I decide to inject anything into the body of my own cats or that of my patients.

Now having said that, we can’t throw the baby out with the bathwater and not vaccinate at all, otherwise our cats (and possibly their humans in the case of rabies) may suffer for it.

Now…for the science:

  • Age of the patient:  Maternally-acquired immunity is an important concept to understand.  When a kitten nurses from his mother, the first milk that she produces (colostrum) is rich with antibodies to fight the various diseases that the mother has been exposed to either naturally from her environment or from any vaccines that she has received prior to giving birth.

(Hopefully all owned cats have been spayed/neutered so as not to contribute to the tremendous overpopulation problem in this world.  Therefore, most cats that have given birth are unowned or wild (feral) cats that have not been vaccinated and only carry antibodies to diseases present in their own environment.)

Maternal antibodies acquired by the kitten inhibit his ability to fully respond to a vaccine.  These antibodies diminish over time and by 16 weeks of age, are at a low enough level in nearly all kittens to allow their immune system to adequately respond to a vaccine.  (Most kittens can respond to a vaccine by 8 weeks of age but we ‘pad’ it a bit to cover those with longer-lasting maternal antibodies.)

Therefore, the last vaccine in the ‘kitten series’ should be given when the kitten is at least 16 weeks of age.

Current conventional protocol states that you can start to vaccinate kittens as early as 6 weeks of age but it would be a very rare situation that would cause me to start vaccinating a kitten at such a young age. 

I find that most kittens that are presented for vaccination are kept indoors and are well-isolated from disease.  If the kitten resides in a protected indoor environment, I feel comfortable starting the vaccine series later than the conventional protocol calls for.  This means that I may not start a kitten’s vaccines until he is ~10 weeks of age, with the second vaccine given at 16 weeks of age.  

  • Risk of exposure:  Does your cat go outside or is he inside 100% of the time?  If he goes outside, is he likely to come in direct contact with other cats?  Is your neighborhood heavily populated with outdoor cats?  How prevalent is rabies in your area?  Etc….

Keep in mind that even though my barn cat is outside and technically has a higher risk of exposure, given the duration of immunity of the panleukopenia vaccine, he is not vaccinated with FVRCP any more frequently than my indoor-only cats.

  • Prevalence of the disease:  The most important disease to consider under this heading is rabies; its geographic prevalence varies widely. 

  • Consequence of the infection:  An infection with herpes or calici is far less serious than an infection with panleukopenia or rabies. Also, keep in mind that the herpes and calici vaccines do not protect the recipient from infection since their efficacy is not as strong as the vaccines for panleukopenia and rabies. Herpes and calici vaccines only lessen the severity of symptoms but will not prevent infection.  This is an important fact as it pertains to the risk-benefit analysis.  (The risk of sarcoma, kidney inflammation, etc., outweigh the small, if any, benefit of re-vaccination.)

  • Health of the patient:  Vaccines are to be administered only to healthy patients.

  • Previous vaccine reactions:  All past vaccine reactions – no matter how minor – must be taken into consideration when making future vaccine decisions.  I will not re-vaccinate any cat that has had an allergic reaction since the next time may bring on a more serious reaction.

  • Vaccine efficacy:  Vaccines vary in their ability to confer strong immunity within the patient.  Some vaccines, such as the FIV (Feline Immunodeficiency Virus) vaccine are not very effective at stimulating immunity in the recipient.  In addition to this issue, the FIV vaccine is a killed product which means it contains an adjuvant.  Therefore, it should not be administered to any cat, in my strong opinion, due to the risk of VAS.

As noted above, Herpes and calici vaccines are also lacking in the ability to induce complete protection.  At best, they will only reduce the severity of some symptoms but will not prevent infection with these viruses and will not protect the recipient from all symptoms of disease.  The risks outweigh the benefits in most situations.

  • Duration of immunity (DOI):  The duration of immunity (how long a vaccine protects the recipient) varies with each disease/vaccine and, of course, with each patient.  However, one vaccine that we do have strong data for is the panleukopenia vaccine which is a very good thing considering how contagious this fatal disease is.

From two different studies, we know that the panleukopenia vaccine confers immunity for at least 7.5 years (the study was stopped at that point) and most immunologists feel that the vaccine lasts for life in the vast majority of cats.  If a cat falls into the rare category of not being protected for life, it is thought that this cat is a ‘non-responder’ and would fail to respond even if further panleukopenia vaccines were given.

  • Vaccine properties:  As I have stated many times, do not ever use an adjuvanted vaccine.

  • Titers:  Note that titer testing is only done for panleukopenia and rabies (for international shipping) and not for herpes and calici.

Think of the immune system as a ‘gun’ and antibodies as ‘bullets’ for the gun.  A titer measures the amount of antibodies for a specific disease that are currently circulating in the blood stream of the body.  This sounds like a great test but the information we get from titer testing is only part of a much bigger picture.

Notice that I emphasized the word “current” in the paragraph above.  This is because of ‘memory cells’ which are cells in the body that titer testing cannot measure.  Memory cells are primed by a previous natural exposure or vaccination to a pathogen (virus, bacteria, fungus, etc.) and are ready to quickly (within hours) produce more antibodies the moment the body is exposed to the invader again.  These cells do not produce antibodies – and therefore, do not contribute to the titer level – until the body is attacked by the pathogen.

Antibodies are not the only type of ‘bullet’ that the immune system uses.  There is another type of ‘ammunition’ called cell mediated immunity (CMI) which is a very important arm of the immune system that, unfortunately, we cannot measure with any commercially available test – including a titer test.

Given the above, it is obvious that titer testing has some severe limitations when being used to assess the status of a patient’s immune system.

So when may titer testing be helpful?

As discussed above, two examples are:

1) to decide if you want to give the 1-year booster after the last kitten vaccine

2) to decide if you want to vaccinate an altered adult cat that came to you with an unknown vaccine history

If an UNaltered stray cat ends up on your doorstep, chances are that he or she has not been vaccinated – and should receive a vaccine now.

Titer interpretation:

If a cat shows any titer at all, this means that he has either been vaccinated in the past (and responded to that vaccine) or he has been naturally exposed to the disease.

According to the World Small Animal Veterinary Association Vaccine Guidelines Group (WSAVA-VGG), a positive test result would lead to the conclusion that revaccination is not required.

Note that a low (versus high) titer does not necessarily mean the cat is unprotected since memory cells and cell mediated immunity are, in all probability, present in full-force.  This is very important to understand because the advent of titer-testing has led to unnecessary revaccination of many patients just because they came up low on their titer test.

A negative titer means that the cat may, or may not be, protected.  The WSAVA-VGG recommends vaccinating these cats while acknowledging  that these patients may be fully protected and not need to be vaccinated.  They are, understandably, taking a ‘better safe than sorry’ approach since panleukopenia is such a serious disease.

If a cat with a negative titer is subsequently vaccinated (with a properly manufactured and handled vaccine) and has his titer re-checked with another negative result, this patient would fall into the ‘non-responder’ category and should not be vaccinated again. 


I wish that I could tell you that there are a straight-forward, clear-cut answers for all decisions involving the vaccination of our cats but there are simply too many variables involved to make this a reality.

As noted above, please understand that I cannot offer any advice via email.  If you wish to discuss your personal situation, I am available for .

In closing, I would like to see less money being spent on over-vaccination of our cats and more money being spent on dental health care which will be the subject of my next webpage.

Preview:  Please consider brushing your cat’s teeth since it is the very best way to maintain their dental health.

And please do not subject your cat to anesthesia-free dental cleanings which provide very little benefit since the problems are under the gum line and these ‘awake’ cleanings only serve to stress your cat and your pocketbook for very little, if any, benefit.

(No cat  is going to let a human probe and clean under their gum line.)

These anesthetic-free cleanings simply result in is a false sense of security leading the cat owner to believe that they have adequately addressed their cat’s dental needs.


Supporting research regarding vaccinations – 2 abstracts:

I put some text in bold.  Please note that Dr. Ron Schultz is one of the leading experts in immunology and is highly respected.

  • Age and Long-term Protective Immunity in Dogs and Cats

J Comp Pathol. January 2010;142S1(0):S102-S108. R D Schultz1, B Thiel, E Mukhtar, P Sharp, L J Larson 1 Department of Pathobiological Sciences, School of Veterinary Medicine, University of Wisconsin-Madison, Madison, Wisconsin, USA.


Vaccination can provide an immune response that is similar in duration to that following a natural infection. In general, adaptive immunity to viruses develops earliest and is highly effective. Such anti-viral immune responses often result in the development of *sterile immunity and the duration of immunity (DOI) is often lifelong.

In contrast, adaptive immunity to bacteria, fungi or parasites develops more slowly and the DOI is generally short compared with most systemic viral infections. Sterile immunity to these infectious agents is less commonly engendered.

*Dr Pierson’s comment:  “Sterile immunity” refers to the immune system preventing infection with the offending agent.  “Non-sterile immunity” refers to the fact that the pathogen can still infect the body (herpes and calici, for instance) but the clinical signs will not be as severe in a vaccinated animal when compared to an unvaccinated animal.  End comment.

Old dogs and cats rarely die from vaccine-preventable infectious disease, especially when they have been vaccinated and immunized as young adults (i.e. between 16 weeks and 1 year of age). However, young animals do die, often because vaccines were either not given or not given at an appropriate age (e.g. too early in life in the presence of maternally derived antibody [MDA]).

More animals need to be vaccinated to increase herd (population) immunity. The present study examines the DOI for core viral vaccines in dogs that had not been revaccinated for as long as 9 years. These animals had serum antibody to canine distemper virus (CDV), canine parvovirus type 2 (CPV-2) and canine adenovirus type-1 (CAV-1) at levels considered protective and when challenged with these viruses, the dogs resisted infection and/or disease.

Thus, even a single dose of modified live virus (MLV) canine core vaccines (against CDV, cav-2 and cpv-2) or MLV feline core vaccines (against feline parvovirus [FPV], feline calicivirus [FCV] and feline herpesvirus [FHV]), when administered at 16 weeks or older, could provide long-term immunity in a very high percentage of animals, while also increasing herd immunity.


  • Membranoproliferative glomerulonephritis possibly associated with over-vaccination in a cocker spaniel.

Ortloff A, Moran G, Olavarria A, Folch H. J SMALL ANIM PRACT 51:499-502, 2010.

This report described a clinical case of membranoproliferative glomerulonephritis (MPGN) in a young dog. The 7-month-old male cocker spaniel presented to the veterinary clinic with vomiting, diarrhea, lethargy, and anorexia. The puppy had been previously healthy with no prior disease, drug treatment, or toxin exposure. However, the puppy had been vaccinated by the owner (without veterinary direction) a total of 7 times (once per month) with a distemper/hepatitis/leptospirosis/ parainfluenza/parvovirus (DHLPP) vaccine.

The puppy was severely dehydrated on clinical presentation and demonstrated pale mucous membranes, oral ulcerations, halitosis, and abdominal pain. Several diagnostic procedures were performed, and ultrasonography revealed loss of renal architecture, increased cortical echogenicity, and bilaterally decreased kidney size.

Complete blood count and serum biochemical values were consistent with renal disease, including anemia, severe azotemia, hyperphosphatemia, and hypoalbuminemia. Urine culture was negative. The puppy was aggressively treated for renal failure, including peritoneal dialysis, but died 3 days after hospital admission.

Necropsy was authorized, and revealed ascites, retroperitoneal and abdominal edema, small pale kidneys, and kidney morphologic changes consistent with glomerulonephritis. Electron microscopy and immunohistochemical testing demonstrated the presence of deposits in the glomerular subendothelial spaces and the basal membrane; this was consistent with antigenantibody immune complexes.

In addition, antigens in the complexes were similar to the vaccine antigens in the DHLPP vaccine, suggesting that the glomerulonephropathy in this puppy was secondary to frequent and unnecessary vaccination.

Commentary: Although membranoproliferative glomerulonephritis is reported as 1 of the most common glomerulopathies in dogs, a definitive diagnosis and identification of the offending antigen are rarely identified due to the risk and expense associated with renal biopsies and electron microscopy.

This case report demonstrates that injudicious use of vaccinations may, like other infectious or autoimmune diseases, lead to immune complex deposition and subsequent glomerular damage.

When possible, appropriate education should be provided regarding the rationale for current vaccine guidelines to avoid overvaccination.

Further studies are required at this time to determine the role, if any, that recent past and current vaccine protocols play in the development of protein-losing nephropathies. Shawn Kearns, DVM, Diplomate ACVIM

 April, 2011

Updated July, 2011

Lisa A. Pierson, DVM

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6 Responses to Vaccines for Cats: We Need to Stop Overvaccinating by Lisa A. Pierson, DVM

  1. Rhonda Wenrich on May 9, 2015 at 9:52 am

    I see no mention in this article about chlamydia. Would you please respond? Is it necessary, (found in the four way vaccines)

    • adminjr on May 11, 2015 at 9:20 am

      Rhonda, I posed your question to Dr. Jean Hofve. She wrote: Chlamydia is an uncommon cause of respiratory infections in cats, which are usually due to feline herpesvirus and/or calicivirus. The Chlamydia vaccine does not prevent infection; and at best reduces (but does not eliminate) symptoms and viral shedding. Like most bacterial vaccines, it requires two shots to be of any use; it does not produce long-lasting immunity; and it carries a higher risk of adverse reactions. It is neither necessary nor recommended.

      Jean Hofve, DVM
      Denver, CO

    • Lisa tave on January 2, 2016 at 6:45 pm

      dr. Pearson stated the vaccinations have saved lives please give me one example of a life that vaccinations have saved

  2. Vaccine Questions to Ask Your Vet - Dogs Naturally Magazine on February 14, 2015 at 4:11 am

    […] at risk for injection-site sarcomas (as are some dogs) and have special vaccination needs. Click here for more details. Also read Vaccination Protocols for Dogs Predisposed to Vaccine […]

  3. Robert Reid on August 31, 2014 at 11:25 pm

    Thanks for the heads up as this has been concerning me for a lengthy time. Very timely. Regards, rgr

  4. Convenia for cats on March 3, 2014 at 10:30 am

    This was cool on “Vaccines for Cats: We Need to Stop Overvaccinating by Lisa A. Pierson, DVM”. I was looking for something like this. Thanks for making my day

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