Unfortunately, new viral strains keep arising for which you have no acquired immunity. The virus spreads rapidly throughout the community by airborne and hand transmission of nasal and throat secretions. The only way to diminish transmission of the virus is for infected individuals to wear protective masks and gloves. In reality, it is not possible to isolate oneself completely from the many viral epidemics which ravage our community. Frequent hand washing and avoidance of close personal contact with individuals affected by the common cold can minimize the chances of catching the disease.
Homeopathic medicines claim to improve one's immunity.
If homeopathic medicines have any benefit it seems to be on the long term and not when symptoms have already manifested themselves. The same can be said for vitamins and mineral supplements. Traditional medicine still maintains that proper nutrition, adequate daily rest and minimizing negative stress in our lives, does more for the immune system than any so-called remedies. What you believe to be recurrent colds may actually be exacerbations of chronic sinonasal infections. Allergies are a common underlying cause.