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Wednesday, July 27, 2011

Titers Vs. Vaccines

Over the last 10-15 years veterinarians and clients have become increasingly concerned about the possibility of over-vaccinating.  This has led to changes in vaccine protocols, studies to determine longer durations for vaccines, and investigation into other methods of preventative care.  One of those potential other methods is measuring titers, something that I get asked about every now and then.

Let's first talk about titers, especially for those without a background in immunology.  When we give a vaccine we stimulate the immune system to react.  In order to help fight off an infection the body will produce antibodies specific to the invader.  These antibodies help immune cells recognize and destroy the organism.  Once the infection is defeated the body wants to be ready in order to repel a similar invasion in the future.  So antibodies against that given organism will remain in the blood stream for a period of time, allowing the body to respond quickly if it is infected again.  Each type of antibody is specific to only a single organism, though some may be similar enough that they will aid in fighting off very closely related organisms.

A titer is a measurement of antibodies in the blood stream.  It's not uncommon for us to measure titers as a diagnostic test when trying to determine whether or not a patient has a given infection.  Some people have been advocating measuring antibody titers to determine immunity before giving a vaccine.  The idea is that if the titer is high then protection is still adequate and vaccination is unnecessary; if the titer is low then immunity has waned and re-vaccination is needed. Sounds pretty simple and makes sense, right?

Unfortunately, it's not so straight-forward.  In fact, top immunologists don't recommend routine titer testing as an acceptable alternative to vaccination.  In the early 2000s the American Veterinary Medical Association published data from a Vaccine Task Force study that had been looking into vaccine protocols for several years.  More recently I read a summary article by one of my professors in vet school, Dr. Richard Ford.  There are numerous reasons why titers aren't a good idea.
1.  Antibody concentration and levels does NOT equal immunity.  A very high level usually indicates protection.  However, a low level may not indicate a lack of protection.  And in the "gray area" between the extremes there is no consensus on what level indicates adequate protection.  So just because a lab report states a given level it doesn't automatically correlate with any degree of protection.
2.  In the US there is no standardized method of measuring serum concentrations of antibodies for vaccine antigens.  Therefore the measurement reported by one lab can be very different than the measurement reported by a different lab!  You can't compare results between labs because they may not be measuring them the same way.  So if one lab gives a "high" result but another lab gives a "low" result, is the pet protected?  Honestly, there's no way to tell.
3.  There are no lab tests for most of the vaccine antigens on the market (currently only for canine distemper, canine parvo, and feline panleukopenia).  However, even if other antibody tests are developed, because the correlation between antibody levels and protection is so poor, results will be meaningless.
4. Vaccines are far cheaper than titer testing.  Most vaccines cost less than $30, yet titer testing for a single antigen may cost $80-100, sometimes even more.  For most cost-conscious clients it's better to give a vaccine rather than test for antibody levels. 

Now I know that there are those out there who are strongly against vaccines and are very in favor of titer testing.  However currently the evidence is against doing testing.  Vaccines have prevented disease for over 100 years and we are improving their quality while decreasing their reactivity.  Vaccines have saved lives and caused minimal problems.  There have been far more problems prevented than caused by immunization, and most of the concerns about them have not been proven despite studies.  So until studies show otherwise, I will continue to advocate for vaccination and against routine titer testing.

7 comments:

  1. Good post. I do not vaccinate my indoor cats anymore, as they are all over 8 years old, were regularly vaccinated as kittens/young cats. I know there was some study floating around out there about 2 rabies vaccines being protective for life.

    Further, I'm not even convinced that the FVRCP vaccine is worth much. I've vaccinated kittens I raised in my house from bottle babies with no hint of URI - only to have them get it later, as young adult cats. Panleuk - yes. Calici and infectious RT - eh...not convinced it's a worthwhile vaccine.

    Now, DH2P, I am a firm believer in.

    That's part of the reason I do ER - I don't have to make those decisions!

    -Homeless Parrot

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  2. I realize you are focusing on vaccinations in animals, but I'm curious: What about (human) rabies vaccination makes titer checking acceptable in humans? That is, which of those factors you talked about isn't similar in human medicine? (I'm guessing standardization might be one?)

    As a student, I know that the requirement is I receive rabies vaccination to start, but in the third year they simply check a titer.So I guess the simple question is: why is that ok for me but not my dog?

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  3. That's actually a good point, and one I've thought of. We also have to measure rabies titers when sending pets to certain countries and Hawaii. These practices don't fit with what we know of titer levels and vaccination. As far as human titers go, I honestly don't know why they're acceptable. Regarding rabies titers for travel, I think it's simply the only way to have even an idea of rabies protection since the only definitive way of detecting the disease is examining brain cells after death.

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  4. Hmm... While I agree titring isn't perfect, I'm not so sure about your reasoning:
    1. Antibody concentration: high level usually indicates protection.but low level may not

    So if you do a titre test and the dog has a high level, you KNOW they don't need a vaccine, so why not test? It may save the dog a vaccine!

    2. In the US there is no standardized method of measuring serum concentrations of antibodies for vaccine antigens.

    Fair enough, but this can be fixed, rather than writing off titring altogether..


    >So if one lab gives a "high" result but another lab gives a "low" result, is the pet protected?

    Has this ever happened?


    3. currently only for canine distemper, canine parvo, and feline panleukopenia

    These three diseases tend to be the ones we're most worried about (rabies being another, which can be titred for).

    4. Vaccines are far cheaper than titer testing.

    Antibiotics are often much cheaper than diagnostic testing. Treating a distended abdomen with Lasix is much cheaper than doing an ultrasound and possibly an aspirate to determine why the abdomen is distended. This isn't GOOD medicine, just because it's cheaper. I don't necessarily think it should NEVER be done, but certainly shouldn't be a justification...

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  5. A takeaway from this article is for those owners whose vets do a titer test and state that the amimal needs a vaccination because the titer is low. The titer test is an antibody test, not an immunity test. The titer cannot evaluate the humoral response, the Bcell memory response. These B cells (memory cells) are the ones that start producing antibodies during an attack. So a pup could ave litterally almost no antibodies and still have immunity.

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  7. When I worked at a vet hospital in Seattle, we would have a VERY difficult time convincing owners to vaccinate at all. It is especially hard to get owners to care about federally regulated rabies when they don't see the disease as a risk. So I think the titers are a good alternative (and argument-ender) that way. A great number of clients opted to pay $250 (from WA IDEXX lab) rather than vaccinate!

    For those that have been indoctrinated by anti-vax hype, "The Vaccine Wars" is an awesome documentary that delves into the anti-vaccine movement, history and importance of vaccines, and shows the consequences of NOT utilizing that science.

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