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Dr. B.
Dr. B., Board Certified Veterinarian
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Experience:  General practice veterinary surgeon with extensive experience in a wide range of species.
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My horse is about to be imported from the USA (where he has

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My horse is about to be imported from the USA (where he has lived all his life) to the UK. He is up to date on his flu and tetanus booster vaccination in the USA but I have been told that when he arrives in the UK it would be best if he starts his flu and tetanus from scratch with the initial course instead of a booster.
Are the flu tetanus vaccines here in the UK slightly different from the USA so that's why it could be dangerous to just booster him when he arrives in the UK?
How does the vaccine work, is there more virus in a booster that in the first vaccine on the starter course? Therefore if he were to get a booster of the flu tet vaccine in the UK and it is slightly different to the booster he has been used to in the USA this new UK booster would be dosing him with quite a large about of a new flu tetanus strain/ vaccine? Therefore that is why it is necessary to start him from scratch again on the initial flu tetanus course? Some clarification on all how the vaccine may differ USA to UK and the way in which starting from scratch on the vaccine course effects the system when compared to just boostering (is boostering a higher doses of virus when compared to first jab on initial flu tet course?)
Thank you,
Hello & welcome, I am Dr. B, a licensed veterinarian and I would like to help you with your wee one today. I do apologize that your question was not answered before. Different experts come online at various times; I just came online, read about your wee one’s situation, and wanted to help.

First, before I can determine what the best course of action is for Chex, I do need to ask:

Do you know the brands of each vaccine he has?

Will your local vet be able to use that same brand here?
Or will then be using a different one?

Hi again Nik,

While I am waiting to hear back from you regarding the specifics for Chex, I do want to explain vaccination for you.

To start, we need to think about what vaccination does. When we give a primary course to an animal, we are actually tricking the body into thinking that these life threatening viruses are very common and therefore it is worth the body’s time and investment to make long term immunity cells (B cells) against these agents. So, when we give the first dose of a primary course, the body reacts as it would to any infectious agent with short term immune cells (T cells) and processes the viruses in our vaccination. But when we follow up with the second jab, the body is fooled into thinking that these agents really are common (since they only fought this off a few weeks back) and it then invests itself into making long term immunity cells. And these cells are what will produce the antibodies and help mount a quicker defense response should they really be exposed to the virus via natural infection. Where boostering comes into this, it is reminder to the body not to toss those long term cells just because it hasn’t actually seen those dangerous agents we told them were so common.

With all that in mind and in regards ***** ***** specific question, every vaccination injection (booster, primary course, etc) contains the same amount of virus. There is usually no difference between US vs. UK core vaccines just because of country; but where variation comes in is with the brands (hence why I asked about those) because the pharmaceutical companies have developed each of their vaccines using their own viral strains (which are only used by them and closely guarded from the other companies). Therefore, if your lad is vaccinated with a brand that they don’t use in the UK, then the advice on restarting his course when he is next due is best since he will not have that the exact long term immune cells to the strain in that alternative brand's virus. That said, since so many vaccine companies are international, if you are using the same brand here as he had in the US (and the datasheet or vaccine company confirm no variation between UK and US brands), then you can just booster.

Overall, the key to which decision to make (booster vs. restarting vaccines) just depends on whether you will be able to give the same brand and thus same virus strain his immune system already knows and has worked with to form his long term immunity. If you can, then only a booster is necessary. If you cannot get that brand, then restarting is ideal to make sure he has long term immunity cells (and doesn't just lose the ones he has because the booster is triggering different responses from the cells).

I hope this information is helpful.

If you need any additional information, do not hesitate to ask!

All the best,

Dr. B.


If you have any other questions, please ask me – I’ll be happy to respond. Please remember to rate my service once you have all the information you need. Thank you and hope to see you again soon! : )
Customer: replied 3 years ago.

Thank you for that information.

I'd like a little further clarification.

If my horse was given a Booster in the UK of a different brand of vaccine than what he was used to in the USA, rather than being started from scratch on the new brand of vaccine in the UK, could this in any way cause him to have an auto immune response?

Thank you

You are very welcome,

If he was given a booster that was not the same brand, then he would only develop short term immunity to the new strain and the long lasting immunity may wane due to not being stimulated by the same viral strain. With time, the boosters may help him make a new long term immunity but this would be a much longer timescale then with restarting the primary course.

Finally, in none of these approaches would we be worried about an auto-immune response since we would not be vaccinated him against himself (and if he has not had an issue with an abnormally sensitized immune system reacting to vaccines with autoimmune issues in the pas, then we'd not expect this with any vaccine no matter the brand).

All the best,

Dr. B.


If you have any other questions, please ask me – I’ll be happy to respond. Please remember to rate my service once you have all the information you need. Thank you and hope to see you again soon! : )

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