Hello and Welcome to ‘Ask A Doctor’ service. I have reviewed your query and here is my advice. When people become hoarse, it means that they have laryngitis. This is inflammation of the larynx, the part of the upper airway that contains the vocal cords. The larynx is in back or the throat. I am unaware of any association between vaccinations and hoarseness. If he has no fever, no cough, and is not breathing faster than normally or breathing using extra effort (muscles of neck would bulge out, skin between ribs would cave in). I believe he will be alright in several days. I hope this helps you. Please return f we can help you in the future.