Over-vaccination has been a bit of a buzzword. Because, obviously, over-vaccinating is a problem…right?

What the heck is over-vaccinating? Where do we draw the line? And is titre testing the answer?

A Crash Course on Vaccination and Immunity

Immunity can be complicated. We have experts who devote their entire lives to studying how the immune system functions.

The immune system, in essence, consists of cells and signalling molecules and biological weaponry. The sole purpose of this system is to defend its host from any insult or threat. You could say your immune system is your personal army. You would be correct.

Army generals could learn a thing or two from your immune system. It is a ridiculously sophisticated system consisting of a hierarchy of soldiers which function as gatekeepers, infantry, spies, snipers…let me just put it this way: the immune system is a really, really well-trained army.

As you may guess, though, these soldiers have vastly different functions and operate very differently. There are different arms to the immunity, generally divided into cellular immunity and humoral immunity.

Vaccination is what we use to trick your immune system into thinking it has been invaded. We can do this in a few ways. We can break microorganisms up into little bits and pieces or we can send in a weakened version of the microorganism. The immune system is trained to go ballistic at this infiltration – it shores up its defences and trains itself to recognise the invader. The next time the invader dares cross its path, the immune system will be ready. The invader is as good as dead.

Here’s the tricky thing. If the enemy came by water, you’d better have a pretty darn good navy. If the enemy is sending rockets, you’d better have something to shoot them down with. Likewise, the immune system has to be appropriately prepared.

Cell-mediated immunity is the arm of immunity that activates specialist killer cells. (Fun fact: Your furbaby has a cell called the Natural Killer cell.) Humoral immunity relies on antibodies which are produced by other specialist immune cells. Antibodies are like crazy AI-controlled robots which detect the enemy and neutralise them – how they do this depends on the type of antibody. Legit, some antibodies behave like Spider-Man and web the invaders, letting these huge garbage collector cells pick them up like the garbage they are.

So, what’s the deal with over-vaccinating?

To be fair, no one can decide what over-vaccinating is. Some would believe that it has to do with vaccinating when immunity is sufficient. Some just don’t like the idea of needles. Some just like to say it for fun.

We know that vaccination can be linked to vaccination reactions. The exploration of vaccination reactions, however, is complex because these reactions can differ depending on the type of vaccine, the adjuvant used in the vaccine, the genetics of the dog/cat, and more. It’s too simplistic to argue that the introduction of an antigen to stimulate immunity is, in itself, harmful. (So we’ll save vaccination reactions for another blog.)

For the sake of this blog, we’ll define “over-vaccinating” as vaccinating a dog or cat when they have sufficient immunity to fight off an infection. That said, drawing this line – trying to decide what “sufficient immunity” is – isn’t that simple.

Some people take a very simplistic view. They say, “Look. We know the body kills invaders with antibodies. Let’s just measure antibodies!”

So, we measure antibodies. And we call this antibody titre testing.

Antibody Titre Tests

An antibody titre test is a test that helps us measure the level of antibodies against specific diseases. But, wait, we know that antibodies aren’t the only way to defend the body. What if I’m measuring the size of the wrong army? How do I know that antibodies will remain for that length of time?

Here’s how they can prove to us that they work. The absolute gold standard is the same test vaccine manufacturers use to prove their vaccines work. To prove a vaccine works, the vaccine manufacturer has to have one group vaccinated and one group unvaccinated. Both groups are exposed to live virus.

There is only one titre test that measures up to this standard. The sample is sent off to the United States of America and has a turnaround of 21 days. It cannot be used to measure antibody levels for Canine Adenovirus-1 which causes the diabolical Canine Infectious Hepatitis – thankfully rare in this part of the world. However, it does correlate certain levels of antibodies to Canine Distemper and Canine Parvovirus with live protection. What it cannot guarantee is how long these antibodies will last.

Other tests use lab tests as their standard which can correlate certain antibody levels with virus neutralisation (VN) and/or haemagluttination inhibition (HI), i.e., protection. Does it translate to real-life protection? Maybe. As mentioned, though, these tests are measured to a completely different standard. It’s going to be hard to know what the long-term effects are; these effects are also likely to differ according to population. However, they are quicker and much, much cheaper.

Also, bear in mind, that these tests only apply to canine core vaccines, that is, the C3 vaccine. The above does not apply to the kennel cough vaccine or to feline vaccines. For our feline furbabies, tests remain unavailable in Australia. Protection against two of the viruses we vaccinate against (Feline Herpesvirus and Feline Calicivirus) just aren’t well measured by antibody tests. But we’ll keep you posted!

In summary, there are a few caveats.

1. The tests can’t tell you, definitively, how long these antibodies will hang around for. Remember, they’re produced by specialist cells. Are those cells available when the threat is present?
2. The tests don’t tell you how good cell-mediated immunity is. Different enemies require different methods of disposal.
3. So far, titre testing only applies to the C3 in Australia.

A few guidelines

We understand, not knowing how the immunity works can be scary. And not knowing how vaccination works can be scary.

We don’t recommend vaccines when dogs or cats are immunocompromised, have certain auto-immune diseases, or if they have certain genetic conditions. Otherwise, we absolutely recommend vaccination because herd immunity protects those who can’t be vaccinated and those whose immunity, for some reason, can’t respond.

We’ve written very generally about these tests because we would like this blog to be relevant to all concerned paw-rents everywhere. If you need more personalised advice, we recommend speaking to your veterinarian. If you’re in a hotspot for parvovirus, for example, your veterinarian would probably really, really appreciate your furbaby being vaccinated.

In summary: your furbaby is an individual! At My Vet, we recommend the triennial C3 vaccine and the annual kennel cough vaccine. But, if you’re thinking of titre testing, come have a chat with us, so we can develop a plan for you and your furbaby.

Do you have any questions about vaccinations? Are you inspired to become an immunologist? Let us know your impressions in comments!

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