Kasiri 2021.

Study characteristics
Methods	Two‐arm, double‐blind, parallel‐group randomised control trial with 4 weeks' duration of treatment and follow‐up
Participants	Location: Iran, single‐centre study Setting of recruitment and treatment: recruited from an outpatient clinic in Ibne Sina Hospital Sample size: 80 Number randomised: 40 to intervention, 40 to comparator Number completed: 39 to intervention, 38 to comparator Participants: Outpatients with severe anosmia or hyposmia, suffering from olfactory disturbance secondary to COVID‐19 for 2 weeks Baseline characteristics: Age: intervention group mean: 35.4 (SD 9) years; control group: 33.2 (SD 8.5) years Gender: intervention group: 20 (51.3%) male, 19 (48.7%) female; control group 19 (50%) male, 19 (50%) female Olfactory function at baseline: intervention group 19 (24.7%) with anosmia, control 21 (27.3%) with anosmia; intervention group 20 (26%) with hyposmia, control 17 (22.1%) with hyposmia (according to Iran UPSIT) Diagnosis of olfactory function at baseline: both self‐reported visual analogue scales and psychophysical testing with the Iran‐SIT were used Duration of symptoms: states that participants "had symptoms of olfactory dysfunction for two weeks" Inclusion criteria for the study: Adult patients aged 18 years or higher referring to the outpatient clinic in Ibne Sina Hospital Diagnosed with COVID‐19 as per clinical findings and real‐time polymerase chain reaction (RT‐PCR) or lung CT scan results Symptoms of olfactory dysfunction for 2 weeks due to COVID‐19 but were not hospitalised Individuals with severe anosmia or microsmia (according to the Iran‐SIT) Exclusion criteria for the study: Hospitalised patients Pregnant or lactating women History of olfactory dysfunction Chronic use of corticosteroids Anatomical abnormalities of the nose, including a history of cancer, rhinitis or surgery Presence of nose bleeds and herpes lesions in the mucosa Declined to participate
Interventions	Intervention group: Intranasal corticosteroid group: 2 puffs of a 100 μg 0.05% mometasone furoate nasal spray, twice daily in each nostril for 4 weeks Comparator group:  2 puffs of topical saline spray in each nostril twice daily for 4 weeks Use of additional interventions in both groups:  Olfactory training was used in both groups, using sniffing of a eucalyptus olfactory pen. No further details on methods of olfactory training or frequency.
Outcomes	Outcomes of interest in the review: Primary outcomes: Presence of normal olfactory function Improvement of olfactory dysfunction defined as the number of patients who returned to normosmia. This was assessed using a visual analogue scale (VAS) (self‐reported) and the Iran‐SIT (psychophysical testing).  All patients reported their degree of anosmia/hyposmia on VAS from 0 to 10 (0 denoting complete olfactory loss and 10 denoting completely normal olfactory sensation) at baseline, after 1 week, 2 weeks, 3 weeks and 4 weeks The Iran Smell Identification Test (Iran‐SIT), which is the Iranian version of UPSIT, uses odours familiar to the Iranian culture. This is a kit containing 24 different types of odours in 8 categories. The test result is reported as a number from 0 to 24, which determines the function of the sense of smell in the range of anosmia (0 to 9), severe hyposmia (10 to 13) mild hyposmia (14 to 18) and normosmia (19 to 24). This measure was administered at baseline and the 4th week of the study. Serious adverse effects  Any side effects from corticosteroid nasal spray therapy were assessed and recorded. There is no further detail regarding assessment or reporting. Change in sense of smell Patient reported change in sense of smell, using a VAS score of 0 to 10, as above Psychophysical testing assessed using the Iran‐SIT 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) Any side effects to corticosteroid nasal spray therapy were assessed and recorded. There is no further detail regarding assessment or reporting. Other outcomes reported by the study: None reported
Funding sources	Research grant funding. This work was supported by a grant from vice chancellery for research affairs of Mazandaran University of Medical Sciences. (Grant number: IRMAZUMS8435).
Declarations of interest	Quote: "The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper".
Notes	No further details in the paper regarding duration of olfactory disturbance, therefore unable to confirm that all participants had symptoms for ≤ 4 weeks. However, authors state that participants had symptoms for 2 weeks, and a large number of participants had symptoms of COVID‐19 at baseline (e.g. fever, sore throat, cough) therefore we have included this study in the prevention review.  There is a discrepancy in the reporting of dates for this study. The recruitment dates are given as "between February 20 and Jun 30, 20201". We note that February 2020 was at a very early stage in the pandemic to start trial recruitment, and the trial protocol states "registered while recruiting" on 20 February 2021, with expected recruitment between 18 February 2021 and 18 April 2021. The paper was submitted for publication on 12 May 2021, therefore recruitment had presumably stopped before June 2021. We have attempted to contact the authors to clarify this.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "Participants in this study were randomly assigned to two groups according to permuted block randomization." "A master randomization schedule was prepared by a person not associated with the study who used permuted blocks of random numbers."  Comment: no further details provided on methods used to generate the random sequence.
Allocation concealment (selection bias)	Unclear risk	Comment: no information on concealment of allocation. Unclear if randomisation schedule was securely held.
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Comment: the trial is described as "double‐blind" and a placebo was used, although no further details are provided.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Comment: study states "double‐blind" and placebo used (topical saline) but no further details provided. No information on blinding of outcome assessors.
Incomplete outcome data (attrition bias) All outcomes	Low risk	Comment: few dropouts, balanced across the groups and fully accounted for (n = 1 lost to follow‐up (intervention), n = 1 lost to follow‐up (control), n = 1 discontinued trial (control))
Selective reporting (reporting bias)	Unclear risk	Comment: primary and secondary outcome measures reported according to protocol. However, protocol was registered whilst recruiting, not prior to study commencing.
Other bias	Unclear risk	Comment: insufficient detail is provided on the conduct of the study to determine whether there may be additional issues resulting in bias. Discrepancy in study dates reported and article submission.