BCCC Education: Vaccination

Vaccination

by Linda Aronson DVM

Together with improved sanitation and epidemiological control vaccination has helped reduce to almost insignificant levels many of the major diseases affecting both humans and animals. It is only because their incidence has been so dramatically reduced that we are now able to address concerns relating to vaccine efficacy and safety. While some problems have been traced to poorly attenuated batches of vaccine that revert to virulence after injection or to contamination, others reflect the animals’ genetic predisposition to adverse reaction.

These reactions may be immediate anaphylactic hypersensitivity; or acute (24 - 72 hours) or chronic (10 - 30 or more days) immunologic responses. The incidence is low. Estimates vary between a low of 1: 1to 3.5 million to a high of 1: 50,000 to 100,000 animals. Part of the difficulty in obtaining accurate estimates comes in the case of delayed reactions when it is sometimes not possible to establish whether the vaccination was causal or coincidental. However, it is also possible that many of these cases will be missed as the relationship to vaccination a month or more earlier will not seem relevant. Unfortunately, predicting which animals will be susceptible is anywhere from difficult to impossible, and if one owns one of those animals which does react the low odds are unimportant.

Anaphylactic collapse is dramatic and life threatening. Animals have been previously sensitized to the antigens in the vaccine. Signs include vomiting, diarrhea, coldness, pale/colourless mucous membranes, loss of voluntary muscle control, rapid breathing and heart rate. It results from the release of histamine and other amines which cause blood vessels to dilate and blood to pool in peripheral vessels. Death may occur before epinephrine and antihistamines can be administered.

Less dramatic reactions may result in fever, stiffness, abdominal tenderness, increased susceptibility to infection, encephalitis, neurological signs, uveitis, autoimmune disease - most often AIHA and/or ITP - and the signs associated with them. Liver and kidney enzyme levels may be elevated, and either organ may collapse. Bone marrow suppression may occur as well. Transient seizures are seen quite often especially in animals prone to thyroiditis or AIHA or ITP. A post-vaccination polyneuropathy has been associated with distemper, parvovirus and rabies vaccines among others. This may result in muscle atrophy, reduced neuronal control of organs and tissues, muscle excitation, uncoordination or weakness and seizures.

Contamination of vaccines has indicated a need for greater quality control during vaccine production. Most notably a canine distemper vaccine was contaminated with sheep blue-tongue virus and led to abortion and death in pregnant bitches. Potent adjuvants are commonly added to killed vaccines to produce a more sustained and stronger immune response. These adjuvants have also produced adverse effects, the worst probably resulting from those added to a killed leptospirosis vaccine which has since been withdrawn from the market. The presence of adjuvants calls into question the supposition that killed vaccines are safer than modified-live vaccines. The latter make up the majority of products available currently. They are easier and cheaper to produce, and elicit a longer and more complete antibody response than killed vaccines. Mixing combinations of MLV products with killed bacterias added in the diluent (common in some multivalent vaccines) appears to particularly stress susceptible individuals. MLV vaccines continue to replicate in the host after injection, and trigger a much stronger response, particularly if given in combination with other vaccines. In most cases this may produce a better immune response but in stressed, immature or sick animals who are genetically susceptible the results can be disastrous. Puppies with their immature immune systems are particularly vulnerable, and should not receive vaccines closer than 3 weeks apart (3 to 4 weeks seems optimal). There is some evidence that over vaccinating puppies (some vets advocate weekly vaccination) can make them more susceptible to chronic debilitating diseases as adults. Dogs with atopic allergies tend to have a worsening of signs after vaccination, and it is better to vaccinate them when their seasonal allergies are not active.

Over-vaccination is a concern. This may manifest not only as vaccinating more frequently than is necessary, but in giving vaccines which are ineffective or prevent infection by agents which produce a mild disease which may not be noticed. Leptospirosis vaccines have provided short lived (3-6 month) protection against serovars which dogs are not presenting with clinically. A new vaccine was promised to combat varieties which dogs are now getting, but I have not heard any more about it recently, and doubt its long term efficacy. Not only has the leptospirosis vaccine been implicated in numerous vaccinosis reactions, but both owners and veterinarians may overlook a diagnosis of the disease in the mistaken belief the dog is immune to it as a result of vaccination. Vaccination against Lyme disease frequently results in positive Lyme titers if the dog is suspected of having the disease. Most Lyme vaccines have limited efficacy. Corona virus does not cause illness in adult dogs and generally only mild disease in puppies. A new vaccine against rotavirus has been introduced although there has been no evidence that it causes disease except perhaps in newborns. Canine hepatitis seems to have been eradicated, yet dogs still routinely receive the vaccine. The administration of each vaccine introduces more foreign substances into the dog’s body with the potential for causing adverse reactions. Meanwhile the owners are having to pay for this. Studies have also shown that immunity induced by giving a puppy series of shots is generally protective for far more than a year, sometimes being effective for life.

A sick dog should never be vaccinated until it is well and recuperated. Vaccination can wait, with the possible exception of the rabies vaccine which some states require be given to the day to consider a dog legally vaccinated (for this reason it may be wise to plan to give a three year shot a month or so early in case the dog is ill when the shot is due). MLV vaccines are shed in the feces for several days after vaccination, and recently vaccinated dogs should be exercised in separate areas from immunocompromised or sick dogs, puppies and pregnant/lactating bitches. Hormonal changes can trigger autoimmune disease, and for this reason it is wise to avoid giving vaccinations before (30 days before expected onset) during or immediately after a bitch’s estrus (heat) period. (It has been shown that giving MLV vaccines to heiffers in estrus induces necrotic changes in their ovaries.) Pregnant and lactating bitches should also not be vaccinated. It can affect their puppies as well as the bitch herself. When should a puppy receive its first vaccination? In North America we usually initiate puppy shots at 6 weeks, in Britain the first shot is not given until the puppy is 10 weeks old and in its new home. Certainly I do not believe puppies should be vaccinated at less than 6 weeks of age, although puppies which did not receive colostrum might represent a special case. Maternal immunity transferred to the puppy in the colostrum has a variable duration, but in general the puppy will respond optimally to the vaccine only when it is 12 weeks old or more. Breed and individual variation within breed can have a significant effect, however. Most dogs have mature immune systems by 22 weeks of age.

In general, all dogs no matter their age or size receive the same dose of vaccine. This makes sense for MLV viruses, but not for killed vaccines. Dose size is based on the minimal immunizing dose for the giant breed and optimal dose has rarely been examined. In humans, attempts to overcome maternal antibodies to measles by giving greater vaccine titers tragically led to high levels of infant mortality, not from measles but from other infectious diseases.

Some breeds of dogs or lines within a breed, or those with double dilute factors may be at such high risk of adverse vaccine reactions that their owners will choose not to vaccinate them. Studies have shown that exposure to shedding dogs, particularly if the unvaccinated individual is a show dog, tends to produce some level of immunity against the illnesses for which the majority of dogs receive vaccination. For dogs which have had previous reactions to vaccines, those whose owners do not wish to risk over vaccination for diseases against which their dog already has adequate protection one alternative is to take titers (commonly available only for distemper and parvovirus) every 2 or 3 years and only vaccinate if titers drop below protective levels. They and owners of geriatric dogs or those with chronic illness may also consider the use of homeopathic nosodes. These are made from an isolate of the particular disease agent. This is prepared as a tincture which then undergoes serial dilutions (potentiation) and succussions (shaking to add kinetic energy). The nosode retains only the energy of the starting isolate and cannot produce infection. While illegal for protection against rabies, nosodes are available for most of the diseases against which there are vaccinations including Lyme disease and kennel cough, as well as heartworm disease. Properly designed controlled studies have not been performed to compare the efficacy of nosodes against allopathic vaccines. A preliminary clinical trial of a nosode for parvovirus failed to protect against challenge from naturally occurring disease. At this point they can only be considered an experimental therapy.

Vaccine manufacturers are being spurred to activity which is perhaps the best result of the vaccine controversy which is being waged in both the veterinary and pet owning communities. In future we can expect to have killed vaccines in doses appropriate for different sizes, breeds and ages of dogs. Recombinant vaccines may also be developed although early experiments have produced unexpected and unacceptable side-effects. Safer, new adjuvants which boost and prolong the effect of killed vaccines can also be expected. So can more research into the length of efficacy of vaccines.

In the meantime, I would recommend asking whether the vaccine you plan to give is needed - is this a disease the dog has any chance of being exposed to, does it cause significant illness in dogs of this age? Is this vaccine effective? If the answer to each is yes, then you may wish to determine whether the dog is still effectively protected against this disease by previous vaccinations (i.e. have blood titers done). If the dog is healthy, not stressed (I would plan to give shots at least 2 to 3 weeks before a trip for example, or avoid them if the whole of your local club will be coming over on the weekend), and has a determined need for the vaccine, go ahead. Watch the dog for at least an hour after the shot. Try to separate shots, especially MLV from killed, by at least 3 weeks. Make sure your dog has regular check-ups, including base-line blood work annually until he’s 10 and then increase the frequency to every 6 months. Even if he seems healthy there may be something you are missing. Do not start puppy shots before 6 weeks of age, and space them every 3 to 4 weeks. Do not worm and vaccinate together, preferably 2 to 3 weeks apart.