NCT04900415.

Study name	Olfactory and neurosensory rehabilitation in COVID‐19‐related olfactory dysfunction
Methods	3‐arm, open‐label, parallel‐group RCT with 4 weeks of treatment and follow‐up
Participants	Adult participants with persisting olfactory dysfunction following confirmed COVID‐19 Inclusion criteria: Aged ≥ 18 years Previous diagnosis of COVID‐19 with laboratory confirmation Subjective complaint of persisting olfactory disturbance Confirmed olfactory dysfunction using butanol threshold test or smell identification test Written, informed consent Available to complete the study and comply with study procedures Exclusion criteria: Inability to comprehend and follow study procedures Allergy or severe reaction to the study drug or smell training Pregnant or breastfeeding women Other causes of olfactory dysfunction (e.g. nasal polyps, anatomical malformations) Received an experimental agent within 1 month, or expect to receive one during the study period Any condition that may interfere with successful completion of the study Estimated sample size: planned enrollment 25 participants
Interventions	Intervention group A Vitamin A 7500 µg plus smell training 3 times per day for 4 weeks Intervention group B Smell training 3 times per day for 4 weeks Comparator: No intervention
Outcomes	Outcomes of interest in the review: Primary outcomes: Presence of normal sense of smell Olfactory assessment using the butanol threshold test and the smell identification test at 4 weeks. Unclear whether these will be reported as dichotomous or continuous outcomes. Serious adverse effects Not reported Change in sense of smell Olfactory assessment using the butanol threshold test and the smell identification test at 4 weeks. Unclear whether these will be reported as dichotomous or continuous outcomes. Secondary outcomes: Prevalence of parosmia Not reported Change in sense of smell Not reported Disease‐related quality of life Not reported Other adverse effects (including nosebleeds/bloody discharge) Not reported Other outcomes reported by the study: Subjective olfactory assessment using SNOT‐22 Neuroradiological changes assessed using MRI
Starting date	22 July 2020
Contact information	Ivan Fan Ngai Hung Email: ivanhung@hku.hk
Notes	Registered in Hong Kong Estimated study completion 30 June 2021 It is unclear if participants will have had symptoms for < 4 weeks at baseline, therefore this study may not be suitable for inclusion in this review. Further details will be obtained when the trial is published.