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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.