prevent epidemics. If the vaccinated animal
does become infected while its immunity is
waning, the partial protection may not prevent
infection but will lessen the severity of the
clinical signs. On the other hand, some studies
indicate that vaccination does not decrease
the intensity or duration of the disease or
enhance subsequent immune responses to future
infections.
The vaccines that are currently available
in the United States contain bivalent or
trivalent chemically inactivated influenza
viruses. Manufacturers recommend an initial
vaccination followed by a booster in 3 to
4 weeks. The animal is then revaccinated
annually. Unfortunately, the young horse
needs more frequent bolstering to maintain
adequate protection so it becomes beneficial to
revaccinate every 4 to 6 months depending on
the potential for reinfection.
Antibodies against equine influenza can be
found in the colostrum of foaling mares. The
half-life of these maternally derived antibodies
in the newborn foal is approximately 35 to 40
days. Vaccination trials have been conducted
on foals that were born to mares vaccinated
approximately 30 days prior to foaling. The
conclusion was that maternal antibodies to
equine influenza interfered with the foal’s
response to the vaccine up to 8 months of age.
Foals from mares that had not been vaccinated
against equine influenza were able to mount an
immune response as young as 2 to 3 months of
age. This proved that young foals can respond
to inactivated vaccines and that maternal
antibodies do interfere with the foal’s response to
influenza vaccine.
This is not to say that vaccination of
the pre-partum mare isn’t recommended
but consideration of each situation should
be considered. It should be taken into
consideration the appropriate time to vaccinate
the foal with an influenza vaccine based on
pre-partum preventative vaccines given to
the mare. It is always recommended that
owners consult with their local veterinarian for
recommendations and guidance on vaccination
protocols.
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