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Equine Influenza and Vaccination: More Myth Busting

When I posted our first article about myths surrounding vaccination for 'flu, I had no idea how popular it would prove to be. Since writing the first blog post, we have spend a huge amount time as a practice speaking to clients, both at yard visits and on the phone, and yes, probably even more time vaccinating horses. Just today I estimate our practice vaccinated in the order of 120 horses across Kent, Surrey, East and West Sussex. 

Of course I believe this is fantastic news for the equine population in our local area, and I hope it is reflective of equine practices across the UK. With the support of the vaccine manufacturers, we and a number of other practices nationwide are offering vaccination amnesty offers for those horses, ponies or donkeys starting or restarting their 'flu vaccines; and the colossally impressive work of those vets and staff of the Animal Health Trust in Newmarket, it appears we are doing our best at keeping this outbreak in check at least. 

However, whilst toottling around (or more accurately flying!) our calls during the recent days a few myths have come to light - some surprising, some less so. So, as promised we've shared these.  

Vaccines represent one of the greatest achievements of medical science, with vaccination being the most effective method for control of infectious diseases.

J.M Daly and P.R. Murcia, 2018
Most recent map of EI outbreaks: 13 Feb 2019 showing the focus on the central and south eastern counties of the UK.

Where are the EI cases now?

Keep an eye out for updates and details on cases as they arise at EquiFluNet:

Vaccination is working!

As we get more details about each focal outbreak detected there is a common theme: clinical signs detected in an unvaccinated horse, then detection of the EI virus in other, often vaccinated, in contact horses. Any vaccinated horse that has been diagnosed with EI so far has either shown no or mild clinical sigs. 

Vaccinating our horses is a critical part of infectious disease control, and together with prompt restriction on mass movement of horses by a temporary ban on racing and mindful attendance at other equestrian events, is proving to keep this outbreak from exploding exponentially.

Want to know more?

​There are huge amounts of chatter around this topic and sometimes it's tricky to sort the wood from the trees. 

We are hosting a complimentary event to discuss The Coughing Horse including Equine Influenza on 27th February at the clinic. Places are limited so book now at

Myth: Shetlands, especially miniatures, should not be vaccinated as they react very badly.

This is a myth that I first came across with respect to tetanus many years ago. I was also told at the same time that the mares's breeder had informed the owner that Shetlands were immune to tetanus and so didn't require vaccinating. All this was immediately after I very sadly put the owner's lovely Shetland mare to sleep as it had contracted tetanus. However, today I heard it again, but about 'flu. I was asked to vaccinate a yard of 10 horses, but the owner was concerned about vaccinating the miniature Shetland as she was told he would get incredibly poorly as a consequence. 

Shetlands, and other miniature breeds, are certainly special little souls with huge characters. They have all sorts of idiosyncrasies certainly, but there is absolutely no evidence to support this statement at all. I have no idea how many Shetlands, American Miniatures and the like I have vaccinated over the years, but I can certainly say that I have not personally noted any one breed type being over represented with adverse reactions. 

Sadly, this is certainly something heard about across the UK as other veterinary colleagues in practice and industry have also heard the myth. but this one is just that. A myth. 

Strategic vaccination can also be used to control the spread of equine influenza during an outbreak. Mathematical modelling has been used to confirm that vaccination 'in the face of an outbreak' can be effective in controlling the spread of equine influenza..

J.M Daly, J.R. Newton, J.L.N. Wood and A.W. Park, 2018

Myth: My horse reacted to his previous vaccine so it's not sensible to vaccinate him again.

As with any medical treatment, adverse events are possible. Bizarrely, if we have a vaccination, we expected a stiff arm; we expect our babies to feel a bit under the weather for a day or so, and we even expect them to run a fever afterwards for a short period of time; yet if horse's experience any of these issues, the belief is that this is an unexpected, adverse event. Is it not a little unrealistic to expect nothing to happen in some horses when we give them a medication to stimulate a development of immunity to a given disease?

Consulting the data sheet that accompanies one particular EI vaccination available several adverse events are recognised a listed. The frequency of these are also quantified. For example, a transient swelling which usually regresses within 4 days may appear at the injection site. In rare occasions, swelling can reach a diameter up to 15-20 cm, with duration up to 2-3 weeks, that may require symptomatic treatment. What does rare mean? This is defined as between 1-10 cases in 10000. In other words 0.001-0.0001%. Not often then. 

Another example. Pain, local hyperthermia and muscle stiffness can occur in rare cases. In very rare occasions, abcessation may be observed.  Very rare is less than 1 in 10000 cases. That's less than 0.0001% including isolated reports. A slight increase in temperature (max. 1.5 °C) may occur for 1 day, exceptionally 2 days. I suspect exceptionally is code for 'someone reported it once'. 

The point is injecting a vaccine may cause some noticeable effect on the horse, but this is not the same as an adverse event. Additionally, just because it happened once doesn't mean it will happen every time. Equally, the transient and short-lived nature of the vast majority of reactions result in temporary discomfort for the horse and inconvenience for the rider or owner in competition animals. Compare this with the welfare implications of contracting disease such as EI whilst being unvaccinated. Protracted time off from work. Significant costs for nursing care. Severe illness or even death of the horse. Is that a trade off worth taking? Not for me it's not. 

The best approach would be to chat to your vet first. There are several strategies we can use to minimise the risk of an adverse reaction from occurring again. Some horses benefit from an alternative brand of vaccination. Some horses react less when given the EI and tetanus components separately rather than in combination within one vaccine. Some horses benefit from concurrent administration of anti-inflammatory drugs, although in the human field this is sometimes discouraged on the basis that the immune system stimulation involves some aspects of inflammation, so there is the potential to reduce the efficacy of the vaccination itself. ​

Many horses never react negatively to vaccination again. For those that have it is a valid concern to both the owner and vet. We will work with you to create a safe a vaccination protocol as possible but avoiding immunisation again potentially fatal disease altogether? I'm not sure I could call that sensible.  

Myth: EI is always around, there are only more cases because vets are testing, so it's all hyped up.

It's true that EI is endemic in the UK horse population. But what does 'endemic' mean and are this number of cases 'always around'?

A disease is described as endemic when it occurs at a constant baseline level in a geographic are without external influence. A handful of EI cases may be diagnosed each year, and in the most recent years these have been attributable to Florida Clade 2 virus strains within the UK. What we are currently seeing is a dramatic rise in the number of EI cases across the UK, coupled with clear evidence that these are caused by a different strain of the virus. Suggesting that the current situation and the normal endemic state are one and the same is erroneous at best and may lead to complacency, resulting in escalation of disease at worst. 

The pattern of detection of disease is also reported to be vastly different. The population of horses experiencing disease include a different cohort - the endemic population being generally isolated unvaccinated horses, compared with this outbreak involving the racing population including vaccinates.  

The high profile media reported has aided vigilance for sure, and vets naturally are acutely aware of horses that may fulfil the typical criteria for suspicion of EI. However, as discussed in the previous blog post testing of animals at the right time is challenging even when we are suspicious and testing is either not performed at all (despite lack of associated costs) or fails to detect disease. Most commonly, negative results are returned because the clinical signs are not caused by 'flu. When presented with a case we sample to identify cause. Swabs are generally run for several respiratory diseases at once: EHV, Strangles, adenovirus, Streptococcus zooepidemicus and more. 'Flu just happens to be on the list. 

The UK surveillance of disease is thorough and reported quarterly to veterinary surgeons. EI is not commonly reported, and if so, tends to be the odd one here and there. So yes, EI is always around. It is endemic. But we are not in that place right now, and this isn't all hyped. Sadly this is an outbreak and we are right to treat it with the respect it deserves lest it gets the better of us.

Myth: My horses aren't vaccinated and they've never been ill before, so there's no reason to start vaccinating now.

Unfortunately, horses don't magically develop immunity to infectious disease. In general, immunity is created after coming into contact with a given disease. This could be after being exposed to the pathogen itself, e.g. around 75% of horses develop a reasonably robust immunity against Streptococcus equi var equi, the bacteria responsible for causing Strangles, once they have come into contact or experienced the disease. On the other hand we can provoke an immunity to be created in a more controlled way by vaccinating. 

In an average year relatively few cases of EI and tetanus are seen in horses in the UK. These are not heavily reported across the country and clients are often unaware that these diseases have been seen. Fortunately, that means there is relatively little likelihood that even an unvaccinated horse will contract disease. This is not an average year and as such, the likelihood of contact with EI is greater. Of course your unvaccinated horse may not get 'flu, but this is relying on luck not judgment. Not many of us would elect to travel to countries which are associated with significant infectious diseases such as cholera, diphtheria, typhoid, hepatitis A without getting vaccinated. Why gamble with your horse's health?

Bear in mind this all applies to any disease we vaccinate against. For 'flu, you could argue that you can reduce risk further by not going out and about and keeping horses isolated, at least during high risk periods. However, that argument doesn't stand up with soil borne bacteria Clostridium tetanii that cause tetanus. Horses could encounter this disease anywhere and it is invariably fatal. We realised that vaccination incurs cost, not insignificant costs for owners of multiple horses. Let's say you have three horses. A 'flu and tetanus vaccine is around £42. To keep vaccines up on a yearly basis carries an ongoing cost of £126. That's £2.42 per week. Not bank breaking when you consider livery, farriery, feed....the list goes on. 

The Coughing Horse
Equine 'Flu: Myth Busting


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Thursday, 17 October 2019

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