Abdelalim 2021.

Study characteristics
Methods	Two‐arm, non‐blinded, parallel‐group randomised controlled trial with 3 weeks' duration of treatment and follow‐up
Participants	Location: Egypt, single‐centre study Setting of recruitment and treatment: recruited at Benha University Hospital Sample size: 108 Number randomised: 54 to intervention, 54 to comparator Number completed: 50 in intervention, 50 in comparator Participants: Patients who have recently recovered from proven COVID‐19 infection, suffering from anosmia or hyposmia Baseline characteristics: Age: intervention group: median 28.0 years (IQR 20.5 to 38.0); control group: median 30.0 years (IQR 22.5 to 39.0) Gender: intervention group: 24 (48%) male, 26 (52%) female; control group: 22 (44%) male, 28 (56%) female Olfactory function at baseline: baseline smell score reported with VAS (0 to 10); intervention group: median 2.0 (IQR 0.5 to 5.0); control group: median 2.0 (IQR 1.0 to 5.0) Diagnosis of olfactory dysfunction at baseline: self‐reported, no psychophysical testing Duration of symptoms: all participants had between 10 and 28 days of olfactory disturbance at baseline (confirmed with study authors) Inclusion criteria for the study: Aged 18 years or older Confirmed case of COVID‐19 (positive PCR) Subsequent recovery (2 negative PCR) Acute onset of anosmia/hyposmia, with or without loss of taste Hospitalised or home isolated Exclusion criteria for the study: Use of nasal steroids for other co‐morbidities Previous chronic rhinological pathology Use of systemic steroids for other systemic disease Anosmia that improved before recovery from COVID‐19 Pregnancy Loss to follow‐up
Interventions	Intervention group: Topical corticosteroid spray (mometasone furoate nasal spray), 2 puffs (100 µg) once daily in each nostril for 3 weeks Comparator group:  No intervention Use of additional interventions in both groups:  Olfactory training was recommended to both groups, in the form of sniffing of rose, lemon and clove for 20 seconds each, twice a day
Outcomes	Outcomes of interest in the review: Primary outcomes: Presence of normal olfactory function Patient reported "complete normal smell sensation", using a VAS score of 0 to 10, where score 10 = completely normal smell sensation. Participants were recommended some substances to use when self‐assessing their olfactory function, such as mint, coffee and garlic. Assessed at baseline, 1 week, 2 weeks and 3 weeks. Psychophysical testing not assessed Serious adverse effects  Not assessed Change in sense of smell Patient reported sense of smell, using a VAS score of 0 to 10, where 0 = total loss of smell and 10 = completely normal smell sensation. Participants were recommended some substances to use when self‐assessing their olfactory function, such as mint, coffee and garlic. Assessed at baseline, 1 week, 2 weeks and 3 weeks. Psychophysical testing not assessed Secondary outcomes: Prevalence of parosmia Not assessed Change in sense of taste Not assessed Disease‐related quality of life Not assessed Other adverse effects (including nosebleeds/bloody discharge) Not assessed Other outcomes reported by the study: None reported
Funding sources	No financial support was reported for the study
Declarations of interest	No conflict of interest was declared
Notes	—
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "The participants in this study were randomly assigned to two groups (simple 1:1 randomisation)".  Comment: correspondence from the author confirmed that adequate methods were used (random selection of groups from an envelope).
Allocation concealment (selection bias)	Unclear risk	Comment: no information was provided regarding concealment of allocation.
Blinding of participants and personnel (performance bias) All outcomes	High risk	Comment: open‐label study, with no placebo group. Participants were aware of their allocation.
Blinding of outcome assessment (detection bias) All outcomes	High risk	Comment: open‐label study, with no placebo group. The only outcome assessed was self‐reported by the (unblinded) participants.
Incomplete outcome data (attrition bias) All outcomes	Low risk	Comment: few dropouts (7.4%) and balanced across the groups. Two participants in each group may have been excluded due to non‐adherence to the trial protocol (intervention group: 1 discontinued treatment, 1 used treatment inconsistently, control group: 2 received other medications). However, the impact of this on the results was not felt to be sufficient to result in high risk of bias.
Selective reporting (reporting bias)	Low risk	Comment: trial protocol accessed on clinical trial registry, and no further outcomes were planned.
Other bias	Low risk	Comment: no other source of bias detected.