How Long Will Your Pet's Rabies Shot Last? You Might Be Surprised...

Story at-a-glance -

  • Dr. Becker interviews Dr. Jean Dodds of the Rabies Challenge Fund to discuss a wide range of vaccine-related topics, including the confusion surrounding antibody titers – what they are and what they tell us about an animal’s protection against disease.
  • Dr. Dodds discusses the difference between “sterile” or lifetime immunity and the short-lived immunity provided by non-core vaccines against diseases like Lyme, lepto, bordetella, other upper respiratory/kennel cough-type viruses, and canine influenza. She also explains why intranasal bordetella vaccines are preferable to the injectable variety.
  • Dr. Becker and Dr. Dodds talk about the various types of antibody titer tests, the issue of conflicting results among tests, the role the animal’s veterinarian plays in decisions about whether or not to re-vaccinate, and the importance of administering single-agent vs. combination vaccines.
  • Dr. Dodds also discusses maternal immunity – what it is, its role in the timing of puppy and kitten shots, and the value in titering at 16 weeks to insure young animals have been immunized and not simply vaccinated.
  • Finally, Dr. Becker and Dr. Dodds discuss the important work the Rabies Challenge Fund is doing to determine the duration of immunity conveyed by rabies vaccines. The goal is to extend the length of time between rabies vaccines to five years, then to seven. The project is in year six of a seven-year study and depends on grassroots funding to conduct the necessary clinical trials. This week only, Mercola Healthy Pets will match every $1 donated by readers with a $2 donation, up to $30,000, to help the Rabies Challenge Fund complete its invaluable work toward reducing the number of vaccines our pets must receive during their lifetime.

By Dr. Becker

Today, I have a very special guest chatting with me via Skype, Dr. Jean Dodds. Dr. Dodds is an incredibly busy woman, and among her many undertakings is her involvement, along with Dr. Ron Schultz, in the Rabies Challenge Fund. The purpose of the fund is to determine the duration of immunity conveyed by rabies vaccines, with the goal of extending the required interval for rabies boosters to five and then to seven years.

Dr. Dodds has agreed to spend some time today discussing antibody titers with us. It’s a confusing topic. Not only are there different types of titers and different methods of titering, but the “when,” “how” and “why” of titering confuses not only pet owners, but veterinarians as well. So I asked Dr. Dodds to start by explaining what a titer actually is.

What, Exactly, Is an Antibody Titer?

Dr. Dodds replied that a titer is a blood sample from which the serum is analyzed to determine the level of antibodies present to an infectious agent like the distemper virus, parvo, hepatitis, and other diseases. When the blood serum antibody level is measured quantitatively, we are measuring a combination of the animal’s natural exposure to the infectious agent as well as vaccinations against it.

Next, I asked Dr. Dodds to explain why some diseases are only acquired once (and thereafter, the animal has lifetime immunity), whereas other diseases pose an ongoing threat throughout an animal’s life.

'Sterile' (Lifetime) Immunity versus Short-lived Immunity

Dr. Dodds explained that certain diseases produce what we call “sterile immunity.” Those diseases include distemper, parvo, and hepatitis in dogs, and panleukopenia in cats. When an animal is exposed to these diseases and recovers, or is vaccinated properly against them, the animal becomes immunized. And we must keep in mind that immunization is the outcome of proper vaccination. The act of administering a vaccine doesn’t necessarily mean the animal has been immunized against the disease.

When an animal is properly vaccinated and becomes immunized, he receives sterile immunity, which is long lasting -- a minimum of seven to nine years, to a maximum of lifetime immunity -- as measured by titer tests. This means the pet cannot become infected, nor will he shed the virus should he be exposed. (Since the diseases of distemper, parvo, hepatitis and panleukopenia are everywhere, the risk of exposure is constant.)

But as Dr. Dodds goes on to explain, there are other vaccines that do not produce sterile immunity. Those are vaccines against Lyme disease, leptospirosis, bordetella, and other upper respiratory/kennel cough-type viruses, and even canine influenza. The vaccines against these diseases don’t last very long – typically seven months to a year. The antibody levels against these diseases, as measured by titer tests, fall off with each successive year.

But… does that mean the animal is not protected against the disease? According to Dr. Dodds, the answer to that question is unclear. There are antibody titer levels, and there are things called immune memory cells, which remain for a lifetime. Even with low titer values following vaccination, pets may still be protected for up to a year or even longer by immune memory cells if exposed to one of these diseases.

Dr. Dodds frames the question this way: “The problem, I guess, is how do you know when you do a titer against one of the shorter-lived agents in terms of duration of immunity… how do you know that the animal is really protected or not? You’re not going to challenge them [by deliberately exposing them to the virus or bacterium] to make that determination.”

Dr. Dodds says that it would seem, for those shorter-lived vaccines, if they’re needed at all – and that’s a very big IF – animals may need to be vaccinated more often, like every 18 months to two years. This is in contrast to the sterile immunity core vaccines for distemper, parvo, hepatitis and panleukopenia, which we should not have to administer after pets reach midlife, as long as they have measurable titer values.

In human terms, we could compare veterinary core vaccines to polio vaccines, and perhaps measles, mumps and rubella vaccines. These vaccines provide lifetime immunity, whereas a tetanus vaccine, which is a bacterin, may not last for a lifetime.

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Why Intranasal Bordetella Vaccines Are Better Than the Injectable Form

Next, I asked Dr. Dodds to talk about kennel cough (bordetella) vaccines. There is the injectable form and the intranasal form. An animal can receive one of these vaccines and immediately be infected with kennel cough.

Dr. Dodds answered that upper respiratory virus vaccines are not 100 percent effective, and in fact, she just received some information stating they are only about 70 percent effective. But there are home and commercial boarding facilities run by people who are really concerned about their own liability, even when the risk is minimal. Some insist on bordetella vaccines every six months. In those cases, the vaccine used should be intranasal.

I asked Dr. Dodds her opinion of the injectable bordetella vaccine. Does she ever recommend it? She replied that she would not, because the intranasal form contains interferon, which provides partial cross-protection against other upper respiratory viruses.

On a side note, the intranasal bordetella vaccine should never be given as an injectable, and the injectable form should never be administered as an intranasal vaccine. Dr. Dodds said recently a Rottweiler received a bordetella vaccine administered incorrectly and acquired acute hemolytic anemia.

Different Types of Titer Tests and the Potential for Conflicting Results

Back on the confusing topic of titers, I asked Dr. Dodds to discuss hemagglutination inhibition, or HAI, because it is a common method some labs use to run titer tests.

Dr. Dodds explained that HAI is the gold standard for measuring immunity to, for example, parvo. It’s the original technique that has been mostly replaced in today’s clinical labs with the more efficient enzyme-linked immunosorbent assays (ELISA) on serum. ELISA tests are quicker and there are very good ones available.

She goes on to say that the parallel to HAI is serum neutralization, SN. It’s considered the gold standard for the canine distemper virus. But again, ELISA tests have replaced SN in most labs because the process is cumbersome, and it is also more costly. The ELISA assays have recently been shown in a refereed paper to give equivalent results to HAI and SN.

I asked Dr. Dodds to discuss another technique called IFA, or immunofluorescence antibody technology. How does it fit into the titering picture? She answered that IFA is something she’s actually quite proud of because back in the late 1990s, she helped develop a similar test and published her findings. In 2000, Dr. Dodds and Dr. Lisa Twark published a very large study of about 1,500 animals, comparing HAI and SN with the new IFA test.

The IFA test measures immunity in much the same way tests detect presence of disease. But as Dr. Dodds explains, vaccine titer levels are typically much lower than disease levels. She likes the IFA test because it simulates what happens with a natural infection – determining how well an animal is protected using the same methodology.

At the major diagnostics lab that runs IFA tests, a “yes” answer to the question of whether an animal is protected actually means the animal is well protected. If a pet isn’t protected according to an IFA test, no question about it, you need to revaccinate except in the case of dogs that have experienced prior adverse vaccine reactions or non-responders – animals that are genetically non- or low-responders to vaccinations, as they simply will not acquire effective immunity to a certain disease no matter how many times they are vaccinated.

Regarding ELISA tests, in my own practice I’ve used them, and noted that some animals show no notable protection against distemper. But when I recheck them with the IFA test, they are protected. This is confusing, and I asked Dr. Dodds about it.

She responded that at her lab, Hemopet, they do their own in-house laboratory titer testing. And they use ELISA technology. If they get a negative on a test – and it’s almost always for distemper – they send it out for an IFA confirmation test. They then provide both sets of results to the animal’s veterinarian so he or she can use professional judgment and case history to decide whether or not to re-vaccinate.

Dr. Dodds explains that she’s not overly worried about a low distemper titer unless the pet is around wildlife. She does worry about parvo. If a parvo titer comes back negative on an ELISA and positive on an IFA, again, the results go to the animal’s vet so he or she can make the judgment call. But Dr. Dodds does discourage vets from delivering combination vaccines and recommends instead a single parvovirus vaccine booster. Single-agent vaccines are significantly less stressful to the body immunologically.

Maternal Immunity: What Is It? Why Is It Important? How Long Does it Last?

I asked Dr. Dodds to talk about situations in which there is potentially some lingering maternal antibody in a young pet, meaning the puppy or kitten is still protected, or partially so, by its mother’s antibodies.

Dr. Dodds first explains that maternal antibodies are what the mother imparts to her litter via the placenta during fetal development – this accounts for up to 10 to 15 percent – and the rest comes from the colostrum in her milk. When the pups or kittens nurse, they receive maternal antibodies. How long those will last depends on how high the mother’s antibody titer was while she was pregnant. Maternal antibodies are usually gone by the time a puppy or kitten is 16 weeks of age, but they start to drop off around 8 to 10 weeks. So there is a “window of vulnerability” between, say, 10 and 16 weeks when young animals are not completely protected.

Our solution for that is to vaccinate earlier, which temporarily suppresses the maternal immunity that is present. But, the animals become more vulnerable for those few days – from about 3 to 7 days – after a vaccination at 7 or 10 weeks, for example. At the same time, the maternal antibodies are waning. It’s not ideal to suppress the maternal antibodies via vaccination, but it’s also not prudent to wait until they’ve dropped off entirely. So it’s a bit of a catch-22.

That’s why it’s important that young pets not be out at dog parks or other locations where potentially infected animals could be. Puppies and kittens should be well immunized before they are allowed to venture out into the world.

Titering from three to four weeks after the last puppy or kitten shot is a good opportunity to determine if the vaccinations actually worked to immunize the animal. Dr. Dodds agrees but says titers shouldn’t be done before 16 weeks, because if you titer earlier, you can pick up some of that waning maternal immunity which will eventually be gone.

Rabies Vaccines and the Exciting Work of the Rabies Challenge Fund

Moving on to the rabies vaccine, depending on what state you live in, it may be approved for dogs as young as three or four months old. This particular vaccine is risky in terms of its reactivity, because it contains a potent amount of inactivated (killed) rabies virus plus strong adjuvants to help stimulate the immune response. Veterinarians often postpone the rabies vaccine until a pet is six months old to give the body more time to develop. I asked Dr. Dodds to talk about the duration of immunity of rabies vaccines, which are made from killed rabies virus.

Dr. Dodds explained that some people believe modified-live rabies vaccines are still in use, but they are not. Years ago, there was a modified-live rabies formula for cats, and it did occasionally mutate and produce rabies. But today there are no modified-live rabies vaccines in use.

However, the killed-virus rabies vaccine is extremely potent and should not be administered earlier than necessary. Even though rabies vaccine package labels say it can be given at 12 weeks, Dr. Dodds believes it should not be given before 16 weeks. Recently, California passed legislation to allow rabies vaccines at 12 weeks vs. 16 weeks, which caused a lot of controversy and will continue to do so.

As to the question of how long rabies vaccines last, according to titer tests, antibodies can remain in an animal’s blood for seven to nine years, and perhaps longer. But again, the question is: are those pets truly protected against the disease?

The Rabies Challenge Fund recently completed year five of its five and seven-year trials to determine how long the rabies vaccine lasts. They are into year six now. The animals used in the study are living in a kennel breeding facility environment.

According to antibody titers on the study animals, at year three after vaccination they all showed good immunity. At year four they showed measurable immunity, but by year 5, some of the animals no longer had measurable rabies titers. Dr. Dodds and Dr. Ron Schultz conducted something called a vaccinal challenge (rabies revaccination) that showed the animals all had immune memory cells that responded by producing good rabies antibody titers, even though some of the animals had titers below the 0.1 international units per milliliter level deemed by the CDC to be adequate to protect a person against rabies. So Dr. Dodds and Dr. Schultz believe that even five years post-vaccination, the animals in the study have maintained good immune memory to protect them against rabies should they be exposed.

What’s lovely about all this is that the animal body is still capable of mounting a response, from immune memory, to the virus. The body innately knows what to do.

Dr. Dodds wants to clarify that even though we know immune memory response was boosted in the animals in the study, it doesn’t mean the USDA or individual states will accept extending the length between rabies booster vaccinations. The Rabies Challenge Fund hasn’t reached that stage in the process yet. They are still developing data that, quite frankly, many people might not want to see published, and that data is being gathered from canine titers rather than trying to extrapolate data from human titer studies to canines.

How You Can Help

The Rabies Challenge Fund study is the first of its kind, and it takes a lot of money to do the work. It’s seven years of research, data collection, and publishing the results. That’s why Mercola Healthy Pets is partnering with the Rabies Challenge Fund to help raise the remainder of the funds needed to not only complete the study, but to insure the research is published in a manner that will benefit the most pets.

Dr. Dodds explained that much of what she has just discussed with us here does not appear at because it could be considered prior publication, precluding their refereed publication (a publication that has been reviewed and examined by experts and scholars in the field of immunology and veterinary vaccines).

And of course research is still ongoing. They are in year six, and have year seven still to go. The project depends on grassroots gifts for funding the costs of conducting the requisite vaccine trials. Contributions to date have come mostly from kennel clubs and private individuals. None of the money collected by the Rabies Challenge Fund goes to Dr. Dodds, Dr. Schultz, Kris Christine, or others working on their behalf. No salaries or other overhead is involved with the exception of expenses for care of the study animals. Dr. Dodds’ staff at Hemopet administers the fund from their offices in Southern California, and all their time and resources are donated.

I want to extend my thanks to Dr. Dodds for talking with us today and for her work with the Rabies Challenge Fund. Thanks also to Dr. Ron Schultz and Kris Christine of the fund. Extending the length of time between rabies vaccinations, thereby reducing the total number of vaccines animals receive during their lifetime, will be a huge benefit to the health and well being of family pets across the globe. Gathering serial serum rabies titer data during the full course of the study also provides a new database to help veterinarians and dog licensing authorities assess exposure risk and levels of protection, especially for those dogs that cannot safely or should not receive a rabies booster.

Mercola Healthy Pets is proud to partner with the Rabies Challenge Fund to raise money to help improve the lives of animals. This week, for every $1 donated to the Rabies Challenge Fund by a Mercola Healthy Pets reader, we will donate $2, up to $30,000.

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