A: You can absolutely work with your veterinarian and reserve some vaccinations for the fall rather than give them all in the spring! Selection of vaccines and when is the most appropriate time to give them is a great conversation to have with your personal vet, as much depends on where you live in the country and what you do with your horse.
Of the core vaccines as defined by the American Association of Equine Practitioners, tetanus and rabies could be given at any time of year because the way that horses contract these diseases is either though a wound, in the case of tetanus, or the bite of a carrier animal, in the case of rabies, neither of which is seasonal. That is, they are not passed by insects or by other horses at equine events.
The other core vaccines are Eastern and Western Equine Encephalomyelitis (EEE and WEE) and West Nile Virus (WNV). These three life-threatening diseases are spread by mosquitos so your vet will want to vaccinate your horse just before the beginning of mosquito season in your area. If you live in a region that hosts a mosquito population year-round, twice-yearly vaccination for EEE, WEE, and WNV may be recommended. However, if you and your horse are located in the more northern climates and do not plan to travel south for the winter, a spring series of boosters should get you through the season and into the fall when cooler temperatures kill off mosquitos.
Moving on to risk-based vaccines, these include protection against such diseases as anthrax, botulism, and strangles, as well as influenza, herpesvirus (EHV or rhino), and Potomac Horse Fever. Just like the diseases above, the main consideration for if and when to immunize against these is based on geography and horse activity. For example, Potomac Horse Fever has a seasonal component to it, so your horse will benefit most if this vaccine is given in the spring. Botulism is endemic in some states — such as the Mid-Atlantic states and Kentucky, along with several western states – but sporadic in others. Strangles commonly affects young horses like weanlings and yearlings but horses of any age can be infected. And new this competition season is the USEF Vaccination Rule, which requires proof of influenza and herpesvirus vaccination within six months of competing.
It can be a lot to try and understand and remember, which is why your vet is your best friend when it comes to proper selection, timing, and administration of vaccines. Some of the diseases mentioned above can be fatal, so why risk your horse’s health by guessing wrong?