Any problem in its chronic stage never allows body to develop immunity in a perfect way. The abnormality of thyroid
from birth is a very big factor. Regarding prevention from cold
you will have to raise the immunity of the body so that minor ailments fail to cause signs and symptoms. In ayurveda we have specific herbs for specific systems as immuno boosters amd for respiratory tract
it is turmeric. we call them as rasayan. To prevent symptoms and problem that has surfaced use sat giloya juice of ginger and honey. Add tulsi in his daily routine. Teach him deep breathing. If there is nasal blockade steam with cap. Karvol
in it is good. continue with thyroid medicine for the tme being. When you get rid of recurrent cough and cold then we can shift for thyroid medicine. Avoid cold things and curd.
Dr. Rajesh Lakhanpaul