This is a preprint article, it offers immediate access but has not been peer reviewed.
“Background: This large-scale cluster-randomised controlled trial (cRCT) evaluated use of facemasks against laboratory-confirmed viral respiratory tract infections (vRTIs) and clinical respiratory infection (CRI) because previous studies have been inconclusive.
Methods: An open label cRCT, conducted in Makkah compared the offer and use of 50 surgical facemasks worn over five days versus no facemasks among pilgrims… Clinical and laboratory data were analysed for facemask efficacy against laboratory-confirmed vRTIs and CRI…
Findings: From October 13 to 17 in 2013, October 2 to 6 in 2014, and September 22 to 26 in 2015, 7,687 adult participants from 318 tents were randomised to facemasks or no facemasks; 3,864 participants from 149 tents were assigned to the Facemask group and 3,823 participants from 169 tents to the Control group. In the Facemask arm, respectively 27% and 51% participants used facemasks daily and intermittently, 22% did not; in the Control arm, respectively 15% and 38% participants used facemasks daily and intermittently, 47% did not. (43%) nasal/pharyngeal swabs from symptomatic pilgrims. In intention-to-treat analysis, facemask use was neither effective against laboratory-confirmed vRTIs (OR 1.35, 95% CI 0.88-2.07) nor against CRI (OR 1.1, 95% CI 0.88-1.39), not even in per-protocol analysis (OR 1.2, 95% CI 0.87-1.69; OR 1.3, 95% CI 0.99-1.83).
Interpretation: Facemask use does not prevent clinical or laboratory-confirmed viral respiratory infections among Hajj pilgrims.”