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Vaccines & Impact on Health

As a veterinarian, I routinely vaccinate patients on a daily basis as a perceived part of preventative health.  Vaccines have certainly saved many lives and prevented many infectious diseases from spreading, but one has to question their timeliness as well as possible negative impact on health as well.

In companion animals, we have the DA2PP (distemper, adenovirus, parainfluenza and parvovirus), bordetella and rabies for dogs and the FVRCP (feline viral rhinotracheitis, calicivirus and panleukopenia) and rabies for cats.  In the horse, we have eastern/western encephalitis, tetanus, influenza, herpes virus (1/4), west nile and rabies.


I believe that many of these vaccines are very efficacious when used properly, but we need to consider the patient as a whole as well as timeliness when administering them.  In all species, we will initially perform a booster series in the juvenile animal or those animals that are naive and have not been vaccinated before.  After this initial booster series, pets are then assigned to a yearly basis and horses to either a twice yearly or annual series.  The rabies vaccine, dependent on the state, can be assigned either a 3 or 1 year status, dependent on age and vaccine history.


One of the biggest factors to vaccinating is viewing the patient, prior to administering the vaccine.  In companion pets, we always perform an examination prior to administering the vaccine, which helps us to determine if there are any concurrent problems that might be complicated by a vaccine.  This may be indicated by an elevated body temperature, evident skin or ear infection or other health conditions that may be raised by the owner. In horses, likely due to expense and time constraints, it was not always routine to examine the patient prior to administering the vaccines.  Often times, as a vet, we had a barn full of horses needing vaccines in a short period of time.  It was just not efficacious to perform exams or body temperatures on all the horses and it was quicker to run through the barn with needle in hand.  This was something we were taught as veterinary students and unfortunately forced to adhere to due to daily work loads and client financial constraints. I have always been in the belief that if my patient had a concurrent health condition, I did not administer vaccines until they have recovered.  Most small animal patients benefited from their exams, but often times equine patients did not. 


Vaccines are designed to stimulate an immune response and are either categorized as modified live or killed vaccines with most vaccines being the later of the two.  Often times, vaccines will have certain adjuvants added to them, which are designed to enhance the immune reaction but also may contain certain preservatives as well.  A killed vaccine contains a modified component of the virus or antigen in which the immune system responds.  A modified live vaccine contains the actual virus or bacteria, but the bug has been inactivated and thus unlikely to produce actual disease but instead just elicit an immune response.  The overall goal is to stimulate an immune response with a ‘memory’, in which if the body encounters that actual virus or bacteria in the future, the immune system will remember it and act accordingly.  The modified live vaccines are considered more potent and more likely to have side effects potentially.


The typical vaccine response is a low grade temperature as well as ‘aches and pains’ for maybe 48 hours post vaccine.  The immune system actually lowers right after the vaccine is administered, then gathers it forces and rises over the next few days.  In some cases, it is common for the animals to have a lump formation in the area of the vaccine due to local inflammatory reactions.  This is most common with the rabies vaccine.  Overall, in healthy animals, the reaction is brief or not present at all and they continue on as normal post vaccine.


The problem that comes is when we administer these vaccines to pets or horses when they are clinically challenged with another condition.  This may be detected by an examination by an elevated body temperature or through observation by the owner, but unfortunately, in many cases this information is tossed to the side and ignored by many.  I have seen puppies exposed to parvo virus be administered a parvo vaccine in hopes of preventing the disease.  The problem here is that the puppy has been exposed and the virus is on board, whether if they are clinically sick or not.  We have to remember that after initially vaccinating an animal or person, the immune system actually lowers, then rebounds.  If the pet has been exposed to the virus, we may be opening the door for the virus to replicate if we lower the immune response through vaccination.  This is indeed what happens in many of these instances and owners are questioning why their pet is sick when they vaccinated them.  This happens all to often with dogs because these vaccines are available over the counter for owners to use freely.  The same holds true for horses, such as in the case of strangles.  I have also seen cases where friends of our have taken their children to the pediatrician due to running a fever, found out they have an ear infection and despite this, the doctor vaccinates the child for the flu or other illness while also prescribing an antibiotic.  My general rule of thumb is if I have a pet or horse that has been exposed to a certain antigen, I will wait 7-10 days before vaccinating, which is adequate time for them to become clinically sick.

Another issue that we often times forget is that we need a healthy immune system to respond adequately to the vaccine.  In many instances, the pet or horse or person, is already challenged by another health condition or maybe they are just not healthy overall.  Here, we can administer the vaccine, but that does not ensure that we will provide a level of protection.  This is seen often in cases of ‘vaccine breaks’ in which animals have been vaccinated, yet become sick when challenged with a certain virus or bacteria.  I don’t think it is reflective of the vaccine as much as it may be reflective of the health of the patient to respond adequately to the vaccine.  One could raise this issue with the human flu (influenza) vaccine as well.  Despite research findings, this vaccine only provide a dismal 5% protection rate based on recent findings.  Why?  Was it the vaccine or was it the patient?  My bet is that it is reflective of overall poor patient health rather than the vaccine. They state that the most ‘at risk’ population for influenza is the elderly, very young or those with concurrent health problems (which is true)…so these are the ones to be vaccinated, right?  Doesn’t make sense to me, as these are the groups that are the most immune and health challenged.  Vaccine administration may help, but then again this is the group of people that may not be healthy enough to respond adequately or worse yet, the vaccine could fuel current health conditions.


We have already discussed concurrent patient disease such as infections being a contraindication to vaccines, but what about other health issues?  Let’s look at allergies, respiratory conditions such as asthma, diabetes, insulin resistance and even cancer.  What is the common denominator with all of these conditions?  There are two:  inflammation and a poor immune response.  If we have a patient with ongoing skin allergies, for instance, that has intermittent skin infections and itching, why would we choose to vaccinate this patient?  All we will do is further aggravate the condition and make matters worse for the patient.  The same holds true for insulin resistance in horses.  How many horse owners have seen the case where a horse becomes lame or mildly laminitic post vaccines?  This response is correlated with insulin resistance and inflammation.  In insulin resistant horses, we have a low level of inflammation that is ongoing, like a smoldering fire.  When we administer a vaccine, it is like putting gasoline on those glowing embers….poof!!  This is why they react the way they do.  Some owners may know they have insulin resistant horses, while others do not.  This type of vaccine reaction in any horse should raise the question as to what else is going on in that patient instead of just treating it symptomatically. Cancer patients are yet another category that should have a thorough evaluation of their vaccine regimen.  These patients are already compromised in terms of health and immune response.  Why would we want to challenge them further and potentially disrupt a state of balance?  Are we more concerned that this patient may come down with influenza or parvo than potentially survive cancer?  This holds true for all vaccines, including rabies, in my opinion.

So, what is the answer?  Vaccines are very effective in preventing disease when used properly, but can contribute dramatically to poor health if used unwisely.  I think we need to evaluate our patients more fully prior to vaccinating to determine if they are healthy enough or not.  I also feel that in horses, we need to split up antigen loads and not give everything at one time, especially in those horses that may be compromised.  The problem with doing this is that splitting up vaccines may take several farm calls or office visits to get the full spectrum.  This may entail added costs for the owner, but in the grand scheme of health, it is warranted.  We need to be more aware of our pets and horses, as well as ourselves, and make educated decisions on what we (as owners) feel is the best thing to do, rather than be persuaded by our veterinarian or barn manager.  In companion pets, I feel we need to be reducing vaccine intervals to every three years, which has been shown to be adequate in many circumstances.  This will help reduce unneeded vaccines and possibly reduce long term effects.


In the end, vaccines are a vital tool in our medicine chest, but they need to be used wisely instead of as a revenue stream for major manufactures.  They are a great means of disease prevention, but are not the only way.  We have to remember the patient as a whole and improve health from a generalized perspective.


All my best,


Tom Schell, D.V.M.

Nouvelle Research, Inc.


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