Fretheim 2022a.

Study characteristics
Methods	Pragmatic RCT
Participants	3717 participants in Norway (glasses n = 1852; no glasses n = 1865) Inclusion criteria: were at least 18 years of age; did not regularly wear glasses; owned or could borrow glasses that they could use (e.g. sun‐glasses); had not contracted COVID‐19 in the 6 weeks prior to participation; did not have COVID‐19 symptoms when providing consent; were willing to be randomised to wear, or not wear glasses outside their home when close to others for a 2‐week period; provided informed consent; and contact lenses were allowed in the control group for those dependent on this visual aid. Exclusion criteria: does regularly wear glasses (contact lenses are accepted); and contracted COVID‐19 after December 15th 2021.
Interventions	Intervention group: wearing eyeglasses (any type) when close to other people outside their home (on public transport, in shopping malls etc.), over a 14‐day period. The control: encouraged not to wear glasses when close to others outside their home. See TIDieR Table (Table 4) for details.
Outcomes	Primary outcome Any positive COVID‐19 test result reported to the Norwegian Surveillance System for Communicable Diseases (MSIS), from day 3 to day 17 of the study period. Secondary outcomes Any positive COVID‐19 test result based on self‐report, from day 1 to day 17 of the study period. Episode of respiratory infection based on self‐report of symptoms from day 1 to day 17 of the study period. Respiratory infection was defined as having 1 respiratory symptom (stuffed or runny nose, sore throat, cough, sneezing, heavy breathing) and fever, or 1 respiratory symptom and at least 2 more symptoms (body ache, muscular pain, fatigue, reduced appetite, stomach pain, headache, loss of smell). Healthcare use for respiratory symptoms, self‐reported, from day 1 to day 17 of the study period. Healthcare use for injuries, self‐reported, from day 1 to day 17 of the study period. Healthcare use (all causes), self‐reported, from day 1 to day 17 of the study period. Healthcare use for respiratory symptoms as registered in Norwegian Patient Registry (NPR), from day 3 to day 28 of the study period. Healthcare use for injuries (from day 1 to day 21 as registered in NPR and the Norwegian Registry for Primary Health Care (KPR), from day 3 to day 28 of the study period. Healthcare use (all causes) as registered in NPR and KPR from day 1 to day 21 of the study period.
Notes	The study did not report on the latter 4 outcomes  due to lack of access to this data at the time of publication. Negative experiences of using the eyeglasses were reported: fogging, feeling uncomfortable and tiring, reduced vision, fall, feeling silly when wearing glasses indoor, headache. Funding: the costs of running the trial were covered by the Centre for Epidemic Interventions Research (CEIR), Norwegian Institute of Public Health. Competing interests: all authors declare: no competing interests.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Automatically randomised after signing the consent form in the online recruitment platform (Nettskjema).
Allocation concealment (selection bias)	High risk	A digital recruitment platform (Nettskjema) was used to generate allocation. However, more participants in the intervention group wore face masks.
Blinding of participants and personnel (performance bias) All outcomes	High risk	An open‐label study. Participants and investigators were not blinded.
Blinding of outcome assessment (detection bias) All outcomes	High risk	Outcome is self‐reported positive COVID‐19 test result reported to the Norwegian Surveillance System for Communicable Diseases (MSIS). However, the public policy requiring  confirmatory PCR‐test had changed during the study conduct which may have affected case detection.
Incomplete outcome data (attrition bias) All outcomes	Low risk	Participants flow chart was provided.
Selective reporting (reporting bias)	Low risk	No deviation from the  published protocol.