We all want our pets to be as healthy as possible – and therefore, to keep them safe from illness and disease. However, with the internet, there’s now a lot of information easily available, and it can be really hard to decide what’s in our animals’ best interests. In this series of blogs, we’re going to look at the basics of Preventative Health for cats – ways that we can prevent problems from starting, rather than trying to react and fix them once they have developed. 
Vaccination has probably saved more lives than any other medical intervention in the last 150 years (except possibly sanitation/freshwater). That goes for animal diseases as much as for human ones – but recently some people have started to question how useful, or even how safe, it is. So, we’ll start off by looking at cat vaccines.
How does a vaccine work?
Although the exact mechanism is really quite complex, in principle, a vaccine teaches the cat’s immune system how to fight an infection, without putting the cat at risk of contracting the disease.
To do this, either a weakened form of the disease-causing organism (an “attenuated” vaccine), or a dead organism (a “killed” or “inactivated” vaccine, usually containing an “adjuvant” – a chemical to trigger the immune system to respond to a dead organism) is introduced into the body. There are also “recombinant” vaccines where a harmless bug (e.g. canarypox virus, which can only cause disease in canaries) is genetically modified to vaccinate the cat against another virus, without causing any different disease. The immune system will recognise it, and take the next week or so learning how to fight it. This means that, when presented with the challenge of the “real thing”, the cat’s immune system can jump on it straight away, without that 4-7 day lag phase.
What can we vaccinate against?
The main vaccines we use are:
? Feline Panleukopenia Virus, FPV; a nasty infection, related to Parvo in dogs, which breaks down the cat’s intestinal lining; at the same time, it attacks their immune system. The symptoms include bloody vomit and diarrhoea, shock, collapse and, in up to 90% of cases, death; unfortunately, the virus can survive for many months in the environment and can be carried into the house on clothing, shoes etc., so even a house cat isn’t safe. Vaccination is highly effective, and has been proven to last a minimum of 3 years in the vast majority of cats. You can learn more about this disease here. Vaccine protection lasts for at least 3 years once the primary course is complete.
? Feline Herpesvirus, FHV; one of the causes of Cat Flu, which although only very rarely fatal, is persistent – once infected, a cat with herpesvirus is likely to remain infected for life, with symptoms recurring and the virus being spread at times of stress. Fortunately, the virus only survives a few days in the environment, so passive spreading of infection is less common. Read more here.
? Feline Calicivirus, FCV, the other major cause of Cat Flu, this virus generally causes slightly less severe symptoms than herpes, but can also lead to stomatitis (inflammation of the mouth), arthritis (joint inflammation), and can occasionally mutate to cause life-threatening disease (Virulent Systemic FCV). Infected cats may shed the virus for weeks or even months before clearing it, but do not usually become persistently infected as with FHV. Like the FHV vaccine, full protection from the vaccine lasts a year, and there is some protection for another 2 years after that.
? Feline Leukaemia Virus, FeLV; this virus is quite closely related to FIV (“Cat AIDS”), but as well as destroying the immune system, can also trigger cancers – typically leukaemia or lymphoma. Vaccine protection only lasts for about a year to most vaccine strains.
There are also vaccines available against Rabies (only needed if you intend to take your cat abroad), and Chlamydophila (“Feline Chlamydia”, another cause of Cat Flu, only usually necessary in catteries or breeding colonies).
What are the risks?
There is no such thing as a medicine without side effects – if a drug cannot produce side effects, it probably means it isn’t actually doing anything. However, the vast majority of these are very mild, typically lethargy, mild inappetence, or itchiness and discomfort at the injection site, lasting 24 hours or so. These are not signs of a problem – they mean that the cat’s immune system is “fighting” the vaccine, which is what we want to happen!
Occasionally, cats may develop more marked symptoms – sometimes vomiting, diarrhoea, lameness, fever, or a transient lump at the injection site. These are usually signs of the same immune activation, but more pronounced. None of these are likely to cause long-term or serious problems for the cat.
There has been a theoretical link made between vaccination and renal disease, however, there is no evidence that this occurs in reality (there’s a summary of a study here demonstrating no effects).
The one adverse effect we really do need to think about, however, is the Feline Injection Site Sarcoma (FISS). Some cats develop an invasive cancer at injection sites (not just of vaccines – the act of inserting a needle through the skin seems to be the primary trigger); it is thought that the use of adjuvanted vaccines may increase the risk slightly, so in cats with a familial history of FISS, a non-adjuvanted vaccine may be advisable. However, this is still a very rare condition – resulting from less than 0.005% of vaccine doses given.
Is it worth it?
For most cats, most of the time, yes.
Natural infection with FeLV, for example, results in more than half of infected cats dying within 3 years; FeLV vaccine reactions are far, far rarer than this (reportedly less than 0.1% of cats developing any side effects that needed treatment); and between 1 and 2% of all UK cats are carrying FeLV and are potentially contagious.
Likewise, as many as 26% of cats are carrying Feline Herpesvirus according to one study.
It is true that many cats who contract infectious diseases will survive them even if not vaccinated. However, this doesn’t take into account the large number of cats who, even if they are a minority percentage wise, are still loved and would be missed by their owners and families if they were to die of a preventable disease. The only reason that these diseases are as rare as they are is because of widespread vaccination, which gives some protection even to unvaccinated animals, by impeding the spread of the diseases through the population.
What about testing the cat to see if they’re immune before vaccinating?
This is a protocol sometimes called titre testing, and it can work for some vaccines. The FPV vaccine, for instance, produces immunity by generating antibodies. If the antibody count is low, the cat needs revaccinating. However, if the antibody count is high, do you revaccinate? It might drop next month, or it might last another year – there’s no way of knowing. If you’d like to go down this route, speak to one of our vets for advice!
Unfortunately titre testing is highly unreliable for FHV and FCV; and it is utterly useless for FeLV as this vaccine doesn’t have to induce antibodies, but can protect the cat by generating a cell mediated response, which we cannot yet test for. If you want to read more about titre testing and vaccine protocols, the WSAVA report is here.