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Why is this important?

Vaccines are the key to protecting cats from infectious diseases such as cat flu, panleukopenia, and even feline leukaemia. These conditions cause untold suffering and even death to unprotected cats, and are all very common in unvaccinated populations.

How do vaccines work?

Vaccines work by "teaching" the cat's immune system how to recognise and fight an infection, without their having to contract it in the first place (and take the risk of chronic long term health issues, severe symptoms or death). Vaccines do not "weaken" the immune system, nor do they "damage" it.

How effective are vaccines?

The effect of vaccination is to reduce the chance that a cat develops a disease; if they are unlucky enough to contract it despite vaccination, it will be milder and they won't transmit it to other cats. Some cats, however, cannot receive vaccination (due to certain immune diseases or medications) so vaccinating other cats in the household, colony or area will help to protect these individuals. In this section, we'll look at the different vaccines commonly available in the UK.

Feline Herpes Virus

This is one of the main causes of Cat Flu, and it also attacks the eyes. It's a particularly nasty virus because once infected, most cats will remain carriers for life, as the virus hides away in their nerves even after they have apparently recovered. When they get ill, or stressed, the virus will re-emerge from hiding again. This vaccine is deemed a "core vaccine" that all cats should receive; it only lasts a year, unfortunately, so after the initial course (two injections three weeks apart) they need annual boosters for life.

Feline Calicivirus

This is the other big Cat Flu virus, but can cause more severe disease as well, including ulceration of the mouth and nose, arthritis, abnormal bleeding, and can be fatal. This is a second "core vaccine", again, it requires two injections three weeks apart and then annual boosters.


This is also known as Feline Parvovirus, and is a nasty aggressive virus that attacks a cat's bone marrow and gut, causing vomiting and diarrhoea followed by collapse of their immune system. It is the third "core vaccine", and after the initial course, it needs a booster one year later and then boosters every 3 years to maximise ongoing protection.

Feline Leukaemia

This virus is spread by close contact (biting, grooming, or sharing food and water bowls) and attacks the cat's immune system. Once infected, the incubation period may last for months or even years, but will eventually destroy their immune system. It can also lead to the development of cancers, particularly leukaemia and lymphoma. The vaccine requires 2 doses 3 weeks apart in kittens, followed by annual boosters.

Feline Chlamydia

This is an uncommon cause of cat flu, and is caused by a bacterium (Chlamydophila felis). Disease is most common in large colonies, especially among breeding groups. The vaccine requires 2 doses 3 weeks apart in kittens, followed by annual boosters.

Can there be side effects?

Vaccines, in most cats, most of the time, are very safe - and certainly, the amount of disease prevented by vaccines is far greater than the amount caused by them. However, they do, very rarely, have significant side effects. The most common noticed effect is minor lethargy for 24 hours after the vaccine; this is exactly what you expect and it means that the vaccine is working, as the immune system meets and analyses the vaccine. Very very rarely, cats may develop allergic reactions, but this is very unusual.

What is an Injection Site Sarcoma?

Injection Site Sarcoma is a widely talked about problem, and it is a genuine risk. However, it's really important to remember that it is quite rare, and also that it isn't strictly speaking caused by vaccination (it used to be called Vaccine-Associated Sarcoma, but this is misleading and so the term has been dropped). Injection Site Sarcomas occur even in cats who have never been vaccinated - the tumour is, we think, caused by injection, not by the vaccine that's being injected.

In conclusion...

Vaccines save cats' lives - its a simple as that. Although very occasionally a cat will develop a side effect, for most cats the advantages massively outweigh the possible disadvantages.