N95 masks may have similar efficacy to medical masks for influenza prevention

1. In this randomized controlled trial among outpatient health care personnel, N95 respirators were similar to medical masks for preventing laboratory-confirmed influenza.

2. N95 respirators and medical masks resulted in similar incidences of acute respiratory illness, laboratory-detected respiratory infections, laboratory-confirmed respiratory illnesses, and influenza-like illnesses.

Evidence Rating Level: 1 (Excellent)

Study Rundown: Health care personnel (HCP) are routinely exposed to viral respiratory infections in the workplace. Some experts argue that N95 respirators and medical masks are equivalent in clinical settings, though this has yet to be demonstrated. In this randomized clinical trial of outpatient providers, there was no significant difference in the incidence of laboratory-confirmed influenza among HCP between N95 respirators and medical masks. Further, N95 respirator and medical mask groups had similar incidences of acute respiratory illness, laboratory-detected respiratory infections, laboratory-confirmed respiratory illness, and influenza-like illness.

Despite this study’s suggestion that these two preventative device are equivocal for influenza prophylaxis, this study has some notable limitations. Participants were not instructed to wear protective devices outside the workplace, which may have biased the results toward finding no difference between groups. Only two N95 respirator and medical mask models were studied, limiting the ability to generalize about the protectiveness of other models. Lastly, the sample size required to definitively determine whether N95 respirators or medical masks are more effective for protection from laboratory-confirmed influenza in the health care setting required significantly more participant seasons than was feasible in this study setting.

Click to read the study in JAMA

Relevant Reading: The efficacy of medical masks and respirators against respiratory infection in healthcare workers.

In-Depth [randomized controlled trial]: 1993 adult participants in 7 US healthcare delivery systems in 189 clusters were randomly assigned to wear N95 respirators (2512 HCP-seasons of observation), and 2058 adult HCPs in 191 clusters were randomly assigned to wear medical masks (2668 HCP-seasons) when near patients with respiratory illness. The primary outcome was the incidence of laboratory-confirmed influenza. Secondary outcomes included incidence of acute respiratory illness, laboratory-detected respiratory infections, laboratory-confirmed respiratory illness, and influenza-like illness. There were 207 laboratory-confirmed influenza infection events (8.2% of HCP-seasons) in the N95 respirator group and 193 (7.2% of HCP-seasons) in the medical mask group (difference 1.0%; CI₉₅, −0.5% to 2.5%). There were 1556 acute respiratory illness events in the respirator group vs 1711 in the mask group (difference −21.9 per 1000 HCP-seasons; CI₉₅, −48.2 to 4.4); 679 laboratory-detected respiratory infections in the respirator group vs 745 in the mask group (difference −8.9 per 1000 HCP-seasons; CI₉₅, −33.3 to 15.4); 371 laboratory-confirmed respiratory illness events in the respirator group vs 417 in the mask group (difference −8.6 per 1000 HCP-seasons; CI₉₅, −28.2 to 10.9); and 128 influenza-like illness events in the respirator group vs 166 in the mask group (difference −11.3 per 1000 HCP-seasons; CI₉₅, −23.8 to 1.3).

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