inclusion criteria: * the subject is aged over 18 years; * confirmed diagnosis of covid-19 at least three months ago (history of positive pcr-testing required) or positive serum nucleocapsid antibody titer against sars-cov2; * post-infectious covid-19 related olfactory dysfunction persisting for at least three months with abnormal sniffin' sticks test (\<13/16 items correct in the identification part); * the patient is willing to undergo odor training over 12 weeks; * written icf is obtained.

inclusion criteria: * the subject is aged over 18 years; * confirmed diagnosis of covid-19 at least three months ago (history of positive pcr-testing required) or positive serum nucleocapsid antibody titer against sars-cov2; * post-infectious covid-19 related olfactory dysfunction persisting for at least three months with abnormal sniffin' sticks test (\<13/16 items correct in the identification part); * the patient is willing to undergo odor training over 12 weeks; * written icf is obtained.

inclusion criteria: * the subject is aged over 18 years; * confirmed diagnosis of covid-19 at least three months ago (history of positive pcr-testing required); * post-infectious covid-19 related olfactory dysfunction persisting for at least three months with abnormal sniffin' sticks test (\<13/16 items correct in the identification part); * the patient is willing to undergo odor training over 12 weeks; * written icf is obtained.

inclusion criteria: * the subject is aged over 18 years; * confirmed diagnosis of covid-19 at least three months ago (history of positive pcr-testing required); * post-infectious covid-19 related olfactory dysfunction persisting for at least three months with abnormal sniffin' sticks test (\<13/16 items correct in the identification part); * the patient is willing to undergo odor training over 12 weeks; * written icf is obtained.

inclusion criteria: the subject is aged over 18 years; confirmed diagnosis of covid-19 at least three months ago (history of positive pcr-testing required); post-infectious covid-19 related olfactory dysfunction persisting for at least three months with abnormal sniffin' sticks test (<13/16 items correct in the identification part); the patient is willing to undergo odor training over 12 weeks; written icf is obtained.

inclusion criteria: the subject is aged over 18 years; confirmed diagnosis of covid-19 at least three months ago (history of positive pcr-testing required); post-infectious covid-19 related olfactory dysfunction persisting for at least three months with abnormal sniffin' sticks test (<13/16 items correct in the identification part); the patient is willing to undergo odor training over 12 weeks; written icf is obtained.