How soon can a horse be ridden after their yearly booster injections?

How soon a horse can be ridden after any kind of injection is debatable among even professionals. However if the horse appears fine and is not stiff in the injection site it is generally okay to ride the horse lightly the same day as the injections were given. If the horse appears stiff or a bit lethargic it might be best to wait a day or so and let the horse work out the soreness himself during turnout time.