EQUINE FLU’ – Are all those vaccinations necessary?

“Ring-a-ring o’ roses, A pocket full of posies,
A-tishoo! A-tishoo!
We all fall down”
                                                                                                                – Nursery Rhyme

Quick Notes:
Equine flu’ is a serious viral illness with recovery taking up to six months. Horses need an initial course of three vaccinations followed by a booster either every 6 or every 12 months (depending on risk and competition regulations). Missing a vaccination or having it ‘late’ means that the course has to begin again, which is sometimes thought to be just a money-making exercise by vets or drug companies but is actually essential for protection of the horse. Without the full schedule, protection wanes and the horse is more likely to get the illness.

More Detail:
Equine flu’ (influenza) is caused by a virus and is readily spread via coughing and nasal discharge. Unvaccinated horses, especially if young, are particularly susceptible and signs include:

  • High temperature (41oC)
  • Harsh cough which can last weeks
  • Watery nasal discharge (snot), which becomes thick and pus-y if a secondary infection with bacteria occurs
  • Depressed and off food (anorexic) – looks ‘sick as a horse’
  • Long recovery period – at least 3 weeks after the coughing stops, with a minimum of 1 week per day of fever. Recovery in severe cases can take 6 months!

Because it spreads rapidly and has a long recovery period most horses are vaccinated. Vaccinated horses can also have symptoms, but these are usually mild.

Why so many vaccination jabs?
Vaccines boost the immunity of the horse; specifically by increasing the number of ‘antibodies’, which are ‘anti’ (against) the invasion of foreign matter that might harm the horse — think of them as ‘flu soldiers’ fighting a war against infection. The horse needs a minimum number of antibodies to have full protection from an invasion of flu’ bugs.

Graph1vaxIn this diagram, the red line represents the minimum level of antibodies needed to protect the horse from infection, and the red arrow is indicating the point in time when the number of antibodies drops below the amount needed to protect the horse i.e. there are not enough flu’ soldiers left to prevent the horse from getting flu’.

Some horses can produce enough antibodies without vaccinations, which is why a small percentage of horses (or people) won’t get infected anyway i.e. they have enough ‘soldiers’ to protect against flu’. However, most horses need vaccinations to keep them above the minimum level needed for protection and at least 70% of a horse population needs to be vaccinated to prevent significant outbreaks.

Some vaccines give protection for years but others don’t. For example, tetanus vaccines protect for a lot longer than flu’ vaccines (see article on tetanus). One of the reasons for this is that the flu’ virus mutates, changing its ‘appearance’ so that it is no longer recognised by the antibodies (flu’ soldiers) that have been made. Therefore, companies that produce flu’ vaccinations for both humans and horses change the formula each year to make sure that the vaccine stimulates antibodies that protect against the latest strains of flu’ i.e. the body will make flu’ soldiers that can recognise the new flu’ invasion.

Vaccination course

  1. Initial injection: this gives protection as shown in the diagram above, but if no further booster is given then the levels quickly drop below the minimum needed.
  2. Second injection 21-92 days later – must be within this range to have the correct effect, so usually given 4-6 weeks after the first injection (which also ties in with a tetanus booster). This injection boosts the antibody levels higher and for longer.
  3. Third injection 150-215 days later (5-7 months). This injection will boost the levels high enough so that the horse will still be protected up to 6-12 months later.

The diagram below shows the protective effect of three injections (yellow arrows) compared to the original single injection given alone.

Graph3vaxBoosters are then repeated 6-monthly (for at-risk horses) or 12-monthly (for horses that aren’t in areas with flu’ cases or travelling a lot to shows/other areas). The FEI ruling states that the booster must be within six months + 21 days (to allow for vaccinations to work around competitions), although the horse is not to be vaccinated within 7 days of the event.

Broodmares vaccinated before foaling will pass protection on to their foals (if the foal gets enough colostrum), and the timing of the first vaccination of a foal will depend on whether or not the dam was vaccinated.

There is a flu’ outbreak in my area; should I vaccinate?

  • If your horse has not been vaccinated regularly and you don’t want your horse to get flu’ then you need to begin a vaccination programme as soon as possible.
  • If your horse has had vaccinations regularly but not within the last six months then you should get a booster vaccination done. Many horses will be protected for the full 12 months but some horses will have levels that have dropped below the level of protection (which is why the FEI requires 6-monthly boosters) and these are at risk of developing the disease and/or spreading the disease to other horses.
  • If your horse has regular boosters and its last injection was less than 6 months ago then you do not need to have another booster yet. The horse should be protected, although remember that vaccinated horses can still get a mild dose of the flu’.

Can I catch flu’ from my horse (or vice versa)?
Human flu’ and horse flu’ are caused by different viruses which can only live in their intended host. So, you cannot catch flu’ from your horse and your horse cannot catch flu’ from you. If both you and your horse have flu’ at the same time then this is just coincidence. However cold and wet conditions can suppress the immune system, which makes infection more likely, so both you and your horse are more susceptible to flu’ during the winter months.

Can my horse catch flu’ from the vaccination?
No. The flu’ vaccination is not giving your horse a dose of the flu’ or the virus that causes it. Instead, the vaccine contains components of the virus or a killed virus that the antibodies can recognise as ‘foreign’ (called antigens). This stimulates the body to produce more antibodies against the flu’ virus i.e. some soldiers recognise a ‘foreign flag’ invading and so more soldiers are recruited in order to protect from any future invasion.

Because the whole live virus is not injected the vaccine cannot cause flu’ by itself. If the horse develops flu’ within a few days of the vaccination it is because the horse was already incubating the flu’, which it has caught from another horse.

The same occurs with humans – often someone will go and get a flu’ jab because they start to feel under the weather or someone in their family comes down with flu. If they are already incubating the flu’ bugs then they may still get a dose of flu’ despite the vaccine because the body has not had enough time to build up the levels of antibody needed for protection (can take 10-14 days), though if you are lucky then the flu’ might be milder than it could have been.

To Sum Up:

  • Is equine influenza (flu’) a serious illness for horses?                                    Yes
  • Will flu’ spread rapidly through a group of unvaccinated horses?               Yes
  • Is one vaccination enough to protect my horse from flu’?                              No
  • Are two vaccinations enough to protect my horse from flu’?                        No
  • Do the flu’ vaccines provide long-term protection?                                          No
  • Can my horse still get some flu’ signs even if vaccinated?                            Yes
  • In an outbreak, should I vaccinate if not done within the last 6 months?   Yes
  • Can I catch flu’ from my horse or vice versa?                                                    No
  • Can my horse catch flu’ from the vaccination?                                                 No
  • In general, should I keep my horses vaccinations up to date?                      Yes

A horse’s vaccination record can be found in its passport. If there is nothing there then it is unlikely that the horse has been vaccinated (although records may have been lost if a passport has been lost and the original vet is not known e.g. imported horses). Therefore it is advisable to start the vaccination programme from the beginning. A combined influenza and tetanus vaccine is available, therefore they can both be given in the same injection (see also the article on tetanus vaccinations).

If you are going to get a human vaccination for flu’, then it is best to have this done before the ‘flu’ season’ begins, to give the vaccine time to take effect and to reduce the risk of catching flu’. There is no guarantee that it will completely prevent flu’, but it can dramatically reduce the symptoms.

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