Question from Jakkii Mickle:

Feline question again- how imperative is having the annual booster jabs for cat flu/ Felv/ Fiv/ Leukemia ? If they have had these injections from kitten age- would they have built up a natural immunity ? One of my cats reacts very badly to these injections, so as a result, I decided not to have them immunised – also my mums dog developed canine leukemia as a result of the injection programme ( confirmed by vets )– so what is best- assume they have their own immunity , or risk them catching these horrible ailments ? Or make them ill by injecting them….???

Answer from Shanika Winters MRCVS, Online Vet

Hi Jakkii and thank you for your interesting question about cat vaccinations. In order to answer your question I will discuss what is in the feline vaccines, what immunity is and how vaccines work.

What diseases are covered in my cat’s vaccine?

Commonly found in the vaccine your vet will offer your cat is protection against feline influenza (cat flu), feline infectious enteritis (viruses affecting the gut) and feline leukaemia (FeLV).  Other feline vaccines available but less commonly given include rabies, Bordatella bronchiseptica (airway disease) and Chlamydia.  There is currently no vaccine against feline immunodeficiency virus (FIV).

What is immunity?

The immune system is the way in which the body detects, reacts and fights off anything it encounters. The immune system is made up of white blood cells (and the substances they produce such as antibodies) and the lymph system (nodules of various size from tonsils through to parts of the spleen).  When the body meets an antigen (something like a virus of bacteria) for the first time certain white blood cells notice the antigen and set off a reaction in the immune system which leads to the development of immunity. Certain white blood cells produce antibodies that recognise and attach to the antigen, other white blood cells come along and help destroy the recognised antigen and some white blood cells keep a memory of the antigen so next time it is met it can be fought off quickly. Once immunity has developed to an antigen the body should be able to fight it off before it can cause illness. Immunity does tend to slowly decrease over time, the longer it has been since an antigen was last met the slower the body is to react to it. This is why booster vaccines are given each year to keep the level of immunity topped up.

Vaccines and naturally being exposed to an antigen stimulate the immune system in the same way to help develop immunity, but vaccines contain antigen that has been treated so as to minimise the chance of developing the actual disease in the process.  The time intervals designed for each vaccine regime are based on research as to how long the immunity levels remain in the average cat.

Generally the antigens in cat vaccines are either a small part of the antigen, an artificially produced version (that is less able to cause disease) or a killed version of the antigen.  This is all done so as to provide immunity with the least risk of your cat actually getting ill.

Why does my cat react badly to the vaccine?

After vaccination some animals feel mildly unwell or can have a slightly raised body temperature, but this is not common. It is also possible for some cats to react badly to some vaccines and develop a full infection. The other thing that cats can react badly to is ingredients in the vaccine most commonly the adjuvant.  Animals that are unwell at the time of vaccination or have an underlying disease can also have bad reactions to vaccines.  This is a large part of why it is important for your pet to have a full health check prior to vaccination.  In the case of your mum’s dog developing leukaemia as a result of vaccinations this is very rare.

The adjuvant is a chemical added to the vaccine to help the cat’s body react more to killed and part antigen components as these would otherwise cause less stimulation of the immune system.  If as is the case with your cat there is a sever bad reaction to vaccination then this should be discussed with your vet, noted on your cats medical records and an attempt made to work out what it is that your cat is reacting to.

Should I still have my cat vaccinated if it reacts badly?

After careful consideration it might be that your cat could tolerate the vaccines if given separately or if a different form of antigen or adjuvant was in the vaccine used.  After many years of vaccination your cat will have developed a reasonable level of immunity but it is very hard to work out exactly how long this will last if annual vaccination is stopped.

In conclusion the decision as to whether or not to have your cat vaccinated every year should be made between you and your vet weighing up the chance of your cat being exposed to various diseases against the severity of its reaction.  I hope that this answer has helped you and your cat.

Shanika Winters MRCVS (online vet)