Is allergy vaccine for child aged 14 safe to prevent him from asthma in future?

Confusing question. I know of no allergy vaccination that can or will prevent asthma in anyone at any age. There are allergy shots that can reduce a persons allergic responses if taken over several years, but not all seem to benefit from them. Allergy by itself has been cited as a triggering factor in only 5-10% of asthma sufferers.
Yes. But always take the caution after the vaccination to be sure there are no serious reactions.