The data regarding the effectiveness of masking as a non-pharmaceutical intervention for influenza transmission, at a glance, seems to be all over the place. This is unlike hand hygiene which is clearly effective.
According to a review by Smith et al, 2015:
In a French cluster-RCT assessing the effectiveness of surgical face masks alone against influenza transmission in community households, no significant differences were noted in the rate of secondary ILI (difference between control and intervention group of 0.40% (95% CI: −10% to 11%, P = 1.00)).
Of course, there is a difference between a healthcare setting and a non-healthcare setting:
Health professionals are at risk of becoming infected when delivering clinical care to influenza infected patients and physical barriers such as surgical masks and N95 respirators have been proven to be effective in acute settings. Using these personal physical barriers in the community is without evidence and does not seem to reduce influenza symptoms or rates of influenza.
According to a review of eight studies by Saunders-Hastings et al, 2017:
…facemask use provided a non-significant protective effect (OR = 0.53; 95% CI 0.16–1.71; I2 = 48%) against 2009 pandemic influenza infection.
A more recent review of ten studies on masks published in 2020 by Xiao et al:
In pooled analysis, we found no significant reduction in influenza transmission with the use of face masks (RR 0.78, 95% CI 0.51–1.20; I2 = 30%, p = 0.25).
Overall…
We did not find evidence that surgical-type face masks are effective in reducing laboratory-confirmed influenza transmission, either when worn by infected persons (source control) or by persons in the general community to reduce their susceptibility.
It seems multiple studies support the view that outside of a healthcare setting, masking is of minimal benefit for preventing influenza transmission.
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S.M.S. Smith et al, “Use of non-pharmaceutical interventions to reduce the transmission of influenza in adults: A systematic review”, Respirology 2015 Aug;20(6):896–903, https://doi.org/10.1111/resp.12541
P. Saunders-Hastings et al, “Effectiveness of personal protective measures in reducing pandemic influenza transmission: A systematic review and meta-analysis”, Epidemics 2017;20:1–20, http://dx.doi.org/10.1016/j.epidem.2017.04.003
J. Xiao et al, “Nonpharmaceutical Measures for Pandemic Influenza in Nonhealthcare Settings—Personal Protective and Environmental Measures”, Emerg Infect Dis. 2020;26(5):967–975, https://doi.org/10.3201/eid2605.190994
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