Linda Arndt ~ Canine Nutritional Consultant

Avoiding Vaccinations During Heat Cycles

Avoiding Vaccinations with Hormonal Imbalance
by Stephen Holt MD

There is a body of scientific literature that cautions against vaccination during changes of hormonal status in animals and humans. Whilst it is recognized that vaccination is best avoided during times of illness, less concern exists about vaccination during major hormonal changes in female pets. The events associated with major change in hormonal status include:

1. One or two months prior to the pet going into "heat" (estrus)
2. During "heat" or one month afterwards
3. During pregnancy or in the early postpartum period (three months after
when lactation is occurring)

Vaccination occurring during the above listed circumstances is believed to contribute to uncontrolled immune aggression and the precipitation of autoimmune disorders.
It is likely that vaccination is risky in circumstances of other types of hormonal imbalance e.g. hyperthyroidism etc. Vaccination during pregnancy has been associated with abortion and when live vaccines are used the fetus or newborn pet may be exposed to viral particles. Some studies have associated vaccination during estrus to be associated with infertility and in cattle
receiving a specific form of herpes virus vaccine, sex gland (ovarian) damage was recorded.

Far to many individuals have ignored the importance of hormonal status at the time of vaccination. I believe that avoidance of vaccination during major changes in sex hormone status in female pets may reduce post vaccination problems. If vaccines are administered during times of hormonal change, close monitoring is required and the administration of nutritional products that help prevent the propagation of immune damage is prudent. In particular, antioxidant therapy with vitamin C and other antioxidants may be useful.
Much more research is required in this area of important animal wellbeing.


Greene CE: Immunoprophylaxis and immunotherapy. In Greene CE, ed: Infectious
diseases of the dog and cat, Philadelphia, 1990, WB Saunders.

Phillips TR and others: Effects on vaccines on the canine immune system, Can
J Vet Res 53:154, 1989.

Phillips TR, Schultz RD: Canine and feline vaccines. In Kirk RW, Bonagura JD,
Current veterinary therapy XI, Philadelphia, 1992, WB Saunders.

Smith CA, editor: Are we vaccinating too much? J Am Vet Med Assoc 207:421,

Wilbur LA and others: Abortion and death in pregnant bitches associated with
a canine vaccine contaminated with blue tongue virus, J Am Vet Med Assoc
204:1762, 1994.

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