African Horse Sickness Vaccinations - Veterinary Association of Namibia

Recommendation for equine vaccinations and competition:

Horses must be vaccinated for African Horse Sickness (with both vaccine 1 and 2) once per calendar year.
As a rule, horses should not be vaccinated with any vaccine within 7 days of a competition. This period is however extended to 21 days for the African Horse Sickness (AHS) vaccine as horses can get vaccine reactions for up to 3 weeks after being vaccinated.
It is strongly recommended that horses are vaccinated during the low vector period (1 June - 31 October) of the year as this will help prevent Culicoides midge transmission of vaccine virus.
If a horse was vaccinated during the high vector period, the horse will not be allowed to a competition for 40 days after the two AHS vaccines.
You need to however decrease exposure to Culicoides midges from the date of administration of the first bottle until 40 days after administration of the second bottle of vaccine. The infective period for AHS in sick horses is considered by the WOAH to be 40 days.
Facts to keep in mind regarding biosecurity and horse movement is that an AHS infected horse can potentially act as a source of AHS virus for midges for 40 days from becoming infected and high viral loads are already present up to 2 days before a horse starts showing clinical signs.