MacIntyre 2015.

Study characteristics
Methods	A cluster‐RCT of cloth masks compared with medical masks in healthcare workers in 14 secondary‐/tertiary‐level hospitals in Hanoi, Vietnam. Hospital wards were randomised to: medical masks, cloth masks, or a control group (usual practice, which included mask wearing). Participants used the mask on every shift for 4 consecutive weeks.
Participants	1607 hospital HCWs aged ≥ 18 years working full time in selected high‐risk wards. Medical mask group (n = 580 HCWs), cloth mask group (n = 569 HCWs), control group (n = 458 HCWs)
Interventions	Medical masks, cloth masks, or a control group. See Table 4 for details.
Outcomes	Clinical respiratory illness, influenza‐like illness, and laboratory‐confirmed respiratory virus infection Clinical respiratory illness, defined as 2 or more respiratory symptoms or 1 respiratory symptom and a systemic symptom Influenza‐like illness, defined as fever ≥ 38 °C plus 1 respiratory symptom Laboratory‐confirmed viral respiratory infection. Laboratory confirmation was by nucleic acid detection using multiplex reverse transcriptase PCR (RT‐PCR) for 17 respiratory viruses. Adverse events associated with mask use
Notes	Government funded. Competing interests: CRM has held an Australian Research Council Linkage Grant with 3M as the industry partner, for investigator‐driven research. 3M has also contributed masks and respirators for investigator‐driven clinical trials. CRM has received research grants and laboratory testing as in‐kind support from Pfizer, GSK and Bio‐CSL for investigator‐driven research. HS had a NHMRC Australian‐based Public Health Training Fellowship at the time of the study (1012631). She has also received funding from vaccine manufacturers GSK, bio‐CSL and Sanofi Pasteur for investigator‐driven research and presentations. AAC used filtration testing of masks for his PhD thesis conducted by 3M Australia.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Epi info V.6 was used to generate a randomisation allocation.
Allocation concealment (selection bias)	Low risk	74 wards randomised prior to recruitment of individuals.
Blinding of participants and personnel (performance bias) All outcomes	High risk	Unblinded study
Blinding of outcome assessment (detection bias) All outcomes	High risk	Unblinded study
Incomplete outcome data (attrition bias) All outcomes	Low risk	No loss to follow‐up
Selective reporting (reporting bias)	Low risk	Specified endpoints reported.