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VETERINARY VIEWS
A strong working relationship between horse owner and equine veterinarian assists in designing an appropriate vaccine protocol that is most effective for each individual.
previous exposure that provides protective immunity.
Compare this to a group of 30 horses
with excellent vaccine protocols against equine influenza. If one or two out of 30 are not vaccinated or have low-level immunity against the virus yet the majority of horses
are protected from infection, then the virus does not become embedded in the group and therefore has limited ability to cause disease in a single, at-risk individual.
The concept of herd immunity is similar to the objective desired by attempting to immunize the bulk of the USA population against Covid-19.
DISEASE PREVENTION PROTOCOLS
The concept of vaccination is to introduce a small amount of pathogen or representative protein from the pathogen, so the immune system “learns” about that protein. Potentially, the greater the arsenal of responding immune cellular memory, the greater the chances of a robust immune response.
A horse’s immune system must be functioning in top shape in order to respond with an optimal level of protection. Every horse is unique in their immune response that is dependent on innate health, age, and environmental exposure. Aging or disease naturally results in some immune system reduction in response. Older horses or those
with disease (Cushing’s or PPID, for example) may need to be vaccinated in a slightly different manner than younger, healthy horses.
Other extraneous factors may influence immune function. Stress, such as experienced during long distance transport and/or
strenuous exercise, directly reduces the level of immune response. It is always best to booster in advance of a stress-related experience so the horse has sufficient time – at least two weeks – to respond optimally to the vaccine(s).
This timing enables a horse time to mount
a sufficient anamnestic (memory) response
and also allows time for resolution of any mild intramuscular vaccine reactions. An exception to the two-week recommendation is a vaccine that activates immunity in a shorter period of time, as for example intranasal influenza vaccine that may provide protection in seven days.
COMBINATION (MULTIVALENT) VACCINE VERSUS SINGLE ANTIGEN VACCINES
Multivalent vaccines – those containing several different disease antigens – provide good host protection from all pathogens included in the various vaccines. One study examined vaccine combinations containing West Nile virus to compare the level of antibody production induced by a WNV-containing multivalent vaccine with that induced by a monovalent, West Nile virus-only vaccine. Investigators found that the level of antibody produced from
a monovalent WNV vaccine was higher than stimulated by a multivalent vaccine containing WNV. There isn’t any evidence that combination vaccines with WNV lack efficacy in inducing an immune response that provides host protection, but maximal protection comes from WNV vaccine given as a stand-alone.
VACCINE REACTIONS
Most vaccine reactions are mild and transient, occurring within 24-48 hours following immunization and resolving within 2-3 days. Reactions involve any of the following: Local soreness or swelling at the injection site, stiff gait, mild fever, lethargy, and/or reduced appetite. More serious but unusual reactions include swollen limbs or colic. On rare occasions, a horse could suffer an anaphylactic reaction, which has the potential to be life threatening.
Giving a horse an NSAID (non- steroidal anti-inflammatory drug, like phenylbutazone or flunixin meglumine) may hasten resolution. If a horse has a known sensitivity, giving an NSAID at the time of immunization forestalls many adverse reactions.
TAKE HOME MESSAGE
A strong working relationship
between horse owner and equine veterinarian assists in designing an appropriate vaccine protocol that is most effective for each individual. Equine veterinarians are knowledgeable about
the specific needs for protection against communicable diseases relative to your geographic area, and they are also familiar with the current and unique state of health of each individual horse. It is always best to consult your veterinarian about which vaccines to give and the frequency that tailors the program to your individual horses and risk.
Herd immunity is important in groups of horses because if all individuals are immunized within a group, then it is less likely that an individual animal will succumb to infection.
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