- previous immunization against covid-19; - allergy to tetracycline hydrochloride; - diagnosis of lyme disease; - immunocompromised; - share housing with someone diagnosed with covid-19 at the time of the baseline evaluation; - serious illnesses, such as cancer, kidney failure, decompensated cardiorespiratory and metabolic diseases, etc.

- previous immunization against covid-19; - allergy to tetracycline hydrochloride; - diagnosis of lyme disease; - immunocompromised; - share housing with someone diagnosed with covid-19 at the time of the baseline evaluation; - serious illnesses, such as cancer, kidney failure, decompensated cardiorespiratory and metabolic diseases, etc.