It takes energy for the body to maintain immunity against a pathogen, which is a waste in the eyes of the body if that pathogen is no longer considered a threat. Therefore, your body’s immunity against a pathogen will fade over time if it is not re-exposed or “reminded” that the immunity is still important. This is what is being achieved when a vaccine is “boostered” – the body is being reminded that the disease is still important to be protected against.
When a vaccine is being developed, before it can be brought to market in the United States, it needs to meet certain standards set by the Food and Drug Administration (FDA). One is that a safety study be performed to evaluate risk(s) and ensure the vaccine is safe to be administered. Another is proof of efficacy – it needs to be able to prevent the disease when the body’s immune system is later “challenged” by exposure to the pathogen.
Challenge studies are how we know some vaccines need to be re-administered – or “boostered” – within a certain time period following a first administration - usually within 2-4 weeks - to provide lasting immunity, while others may not. When pet vaccines are being developed and are seeking FDA approval, a one year trial is commonly performed to prove efficacy. If a one year trial was performed, these vaccines will typically be “boostered” again after that one year period, because effective protection was not demonstrated or proven past that point. If a two year, three year or longer challenge study has been performed by the company or a university and longer-term protection can be proven, then the frequency of re-administration can be reduced accordingly. The overall goal is ensuring reliable protection against the targeted disease.
In theory, protective immunity after some vaccines may last longer than the labeled duration of proven immunity. For some antibodies, “titer testing,” which looks at the quantity of antibodies in the blood can be performed. This test is currently available for Canine Distemper Virus and Canine Parvovirus, allowing a dog to receive a boostering vaccination when the titers drop below a “protective level” determined by previous scientific studies. Titer testing is also available for Rabies Virus antibodies, but it is not recognized as proven protection by State laws, so we consider Rabies titer testing to be a waste of money at this time, unless it is required for international travel.
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