Our cats are, sadly, vulnerable to a wide range of different infectious diseases. Some of these are serious, often causing life-long complications, and they may even be fatal. However, unless you keep your cat indoors all the time, they never go outside, and you never have any visitors (human, cat or other animals), there’s no way to guarantee that they won’t be exposed to these infectious organisms.

Why do we vaccinate?

We vaccinate to maximise your cat’s protection against infectious diseases. A vaccination is basically a way of educating your cat’s immune system so that if it ever sees the infection for real, it knows how to deal with it in the most effective way – minimising the risk that they will develop the full blown disease.

How do vaccines work?

When a cat’s immune system is first challenged by a new foreign invader (a bacterium, a virus, or a parasite), it tries to kill the invader by producing antibodies, or sending white blood cells to destroy infected cells. However, it doesn’t know which type of antibodies to make, or which type of white cell to send. So it learns by trial and error – no, that antibody doesn’t work, nor does that one, that white cell can’t do the job, etc. etc. It may take several days of frantic activity before it finds the right response. In a really severe infection, like panleukopenia or feline leukaemia virus, that may be too late – the infection may have become too established in that time for the immune system to defeat it.

When we give a vaccine, we are administering a weakened, or even dead, form of the infection. The immune system will still attack it, but if it takes a few days or even a week to work out how to kill the bug, that doesn’t matter – we know that the vaccine strain cannot cause the full blown disease.

So, the cat’s immune system knows how to fight the infection if ever they come into contact with the “real deal” in the wild. However, vaccines also protect cats on a wider basis too – not every cat can safely be vaccinated. Some are too young; some might have diseases of their immune system, or be on medications, that mean they cannot respond properly to the vaccine. But, if enough other cats around them are vaccinated, even these individuals have some degree of protection, because a vaccinated cat is not only very unlikely to develop an infectious disease, but they are also highly unlikely to spread the infectious organisms on to other cats.

So, what can we protect our cats against?

There are a number of different vaccines available in the UK for our cats; some of these are considered “Core Vaccines” – those that every cat should have to protect them and the whole feline population from common diseases. Others are more optional, and are recommended based on the specific risks your cat has based on their location and lifestyle.

Feline Pankeulopenia Virus – Core Vaccine

This is a really nasty disease, which attacks the gut lining and the cat’s immune system. The virus causes bloody vomiting and diarrhoea, collapse, dehydration and, sadly, is often fatal. It is a common virus, and outbreaks are fairly frequent, partly because the virus can survive for prolonged periods in the environment, and can even be carried on people’s shoes or clothing. You can learn more about this disease here; fortunately, vaccination is highly effective and offers powerful protection. Once the primary course is completed, (2 shots 3 weeks apart, then a booster a year later), protection has been proven to last for 3 years before a repeat vaccine is needed.

Feline Herpes and Calicivirus – “Cat Flu” – Core Vaccines

These are always given together, as they are the two most common causes of Cat Flu, a really nasty respiratory infection in cats. Although fatalities are rare, chronic infection for life is the norm with cats who develop feline herpes – they carry the virus with them for life, and at times of stress, it can reactivate. Learn more about Feline Herpes and Feline Calicivirus from the International Cat Care website.

These vaccines are fairly good at preventing infection, but their main role is in reducing the severity of an infection, and the risk of the cat spreading the bugs to anyone else. However, immunity doesn’t last very long – cats should be revaccinated annually to maintain their protection.

Feline Leukaemia Virus (FeLV)

This is a really strange bug – it is quite closely related to HIV, that causes AIDS in humans, but as well as causing the cat’s immune system to collapse, it can also trigger the development of cancers of the white blood cells (usually leukaemia or lymphoma). This is NOT the “cat AIDS” virus (Feline Immunodeficiency Virus), but fortunately can be prevented with vaccination, unlike FIV. Feline Leukaemia Virus can also be spread in saliva by grooming, sharing food bowls, or fighting, so vaccination is really important for cats who live in high-cat population areas.

Again, however, immunity doesn’t last long, and at the moment we recommend annual revaccination.


Fortunately, your cat only needs this vaccine if they’re going abroad – rabies is not yet found in the UK! If you are going abroad with your pet, however, your cat MUST be vaccinated to return to the UK, unless you’re willing to put them into Quarantine on your return.

Although other vaccines for some conditions (e.g. Feline Chlamydia, another cause of Cat Flu) are available, these 5 are the most important ones.

Are vaccines harmful?

Unfortunately, there is no such thing as a medication without any side effects (if it cannot cause side effects, it probably means it isn’t doing anything). However, the vast majority of cats will not show any ill effects. If they do, these are almost always mild signs of immune activation, e.g. lethargy, tenderness at the injection site, or occasionally mild sniffles. These rarely last more than 24-48 hours.

There is no evidence that “over-vaccination” causes immune problems, secondary diseases or developmental disorders in kittens.

The only major health threat that can be linked to vaccination is Feline Injection Site Sarcoma. As the name suggests, this arises at injection sites, and also occurs in cats who have never been vaccinated, but have been injected with other products. It is thought to be an abnormal response to inserting a needle through the skin, rather than to the vaccine itself. It causes a lump to form, which instead of going down after a few days, keeps growing; this is a form of tumour that invades the local tissues. It doesn’t usually spread around the body, but can be difficult to remove surgically. However, this is very rare – probably less than 0.005% – whereas the diseases prevented by vaccination are much more common (1-2% of cats have FeLV, and as many as 26% carry feline herpesvirus according to one UK study).

If you want to know more about vaccination, come in and talk to one of our vets!