Vaccinations And Immune Response Titres:
The first vaccine was produced in 1798 when a scientist named Jenner determined the low-grade cowpox virus could be used to protect against deadly smallpox. Since then, many, many vaccines have been created for a large number of diseases. Some of these vaccines have been used to an extent that its correlating disease has been eradicated. Now, there are questions about whether vaccines should be used, and whether we are over-vaccinating.
This blog is focused on talking about how vaccines work, why they are dosed as they are, what the decision points are around necessary “booster”ing of vaccines, and new options for decision making.
First, two words need to be defined: vaccination and immunization.
Vaccination is the administration of a pathogen in a form that is either rendered incapable of causing the disease (killed vaccine), or made as to be too weak to cause disease (modified live), but strong enough to induce a response from the immune system. This response is intended to stimulate the body to make antibodies to the pathogen (“bug”). When this happens, the body is smart enough to also create memory cells, so that if this same “bug” is introduced to the body again, it remembers the stimulus, and makes the same neutralizing antibodies even faster. This is important because when we are exposed to disease, the faster we make protective antibodies, the less likely we are to become ill.
Immunization is the state of having protection from a disease after vaccination; please note that having a vaccine does not necessarily mean you have immunization.
This is for a couple of reasons, n the very young, maternally transmitted protection (e.g. in colostrum) will reduce the ability of the newborn to respond to vaccines. This is why vaccinating puppies and kittens younger than 7 or 8 weeks is often ineffective, and why multiple boosters are given: we want to have the vaccine present as soon as they can respond so we can protect them, and we don’t know exactly when maternally transmitted protection will drop enough for this to happen. Some bodies simply do not generate a response to some vaccines, even when they have been given multiple times. This is kind of scary, we assume they have been protected because they were vaccinated, but we may be unaware that they are not actually immunized. This leaves them perpetually at risk for this disease. Some diseases really require more than one vaccine to stimulate an adequate immune response, so if the patient was not given the appropriate number or appropriately timed boosters, they may not become immunized.
Other reasons why immunization may not happen after vaccination include; poor storage or handling conditions of the vaccine and improper administration. This is why appropriately trained personnel and fridge thermometers are important!
Statistically, 55% of dogs and 60% of cats whose last vaccine was at 12 weeks of age are not immunized; up to 15% of dogs whose last vaccine was at 16 weeks still are not immunized. One in 1000 dogs simply do not respond to parvo vaccinations.
There are different types of vaccines – killed and modified live.
The killed vaccines are rendered incapable of causing disease; modified live (MLV) ones (like human flu vaccine for example) cause very low grade disease to stimulate the immune system. Killed vaccines absolutely require two doses to generate an adequate immune response; with MLV vaccines the vaccine both primes and immunizes the system. With puppy and kitten vaccines, as previously noted, because there is maternal antibody lingering in their systems, we need to provide multiple doses to catch them as soon as they might become responsive to give them the best protection.
The body does not create memory equally amongst pathogens. For viral diseases, like parvovirus, the body tends to retain the ability to remember and will make antibodies quickly. For bacterial diseases, like Lyme disease (Borrelia sp.) and canine cough (Bordetella sp.), the body does not remember very well, and these need to be boostered annually to maintain good protective levels of antibodies.
Consider for example canine cough vaccine, which has both killed and MLV versions. One dog receives the MLV version and does not need to have it boostered; the other dog receives the killed vaccine version and does need a booster in 3-4 weeks. As this vaccine does not confer long term immunity (bacterial, not viral), it needs to be boostered annually. Think of this as the immune system being primed as you would a pump that was unused for a while.
The value of vaccination is in the prevention of disease. Probably not many people remember the huge losses of dogs from distemper in the early 1900’s, but many people will still remember the huge parvo epidemic in the late 1970’s; the first distemper vaccine was produced in 1933, and parvo vaccine in 1978. These diseases are deadly, and indeed are still occurring today, although gratefully in much, much lower numbers because of vaccines, and the percentage of the pet population that is now vaccinated. Epidemiology is the branch of medicine that deals with the incidence, distribution and control of diseases. It looks at things like, if 60% of the population is protected, how likely is it that the 61st dog is going to get sick? This is where the concept of “herd immunity” comes from; essentially it is a game of risk management. How much are you willing to risk that there is enough community protection out there to protect your unvaccinated pet?
Another current topic is, are we over vaccinating? This is a great question, and is one of the drivers for checking vaccine titres. Studies indicate that after 12 months, bacterial/killed disease vaccines tend to lose their ability to be protective, and are recommended to be boostered annually.
Many viral vaccines can confer immunity for years once the immune system has been adequately stimulated, though. For years these vaccines were given annually, because 1) it created control of an endemic situation 2) they were tolerated 3) it took time to create an adequately protected population to reduce disease incidence. Then the era of questioning the dose frequency began.
Studies showing duration of immunity (DOI) were lacking, and a combination of fear of disease resurgence and legal backlash for not following manufacturer label claims created reticence to reduce dose frequency. DOI studies are costly, take many years and many dogs to run, and longer still to compile and publish the data. Eventually those became available and published, and this created change to the currently recommended 3-year protocols.
Now, in an era driven by the desire for information and the answer to “why”, and in a time when technology can deliver solutions to market more quickly than before, we have titres available for some diseases to help answer the question of whether we need to vaccinate again, yet, or not. Dog vaccine titres have become more readily available; sadly, cat vaccine titres are lagging behind.
Titres are measurements of the immune response of antibodies in the blood to a pathogen in a petri dish. This is interpreted as a likelihood of protection. Titres do not however forecast the strength of the immune response, but simply show that antibodies are present. So when are titres actually helpful?
Some good examples of use for titres include:
-To see if young dogs have actually responded to vaccine and are immunized (or are non-responders)
-To see if there is a need to re-stimulate the immune system. This is especially applicable in older dogs where, like humans, the immune system weakens in older canine patients. This puts them at greater risk, and is akin to puppies and human babies being of higher risk for getting diseases.
-In cases where there is a history of a concerning immune reaction to a previous vaccine, a chronic illness, or other concurrent disease so levels of protection can be identified, and appropriate risk management strategies invoked.
The immune system is pretty amazing, but also pretty complicated.
If you have a curiosity for more information, or would like to discuss the option of checking titres instead of vaccination, please contact us to book an appointment. We would be happy to share our knowledge!