Efficacy of N95 Respirators, Surgical Masks, and Eye Protection against Influenza Droplet Transmission

Background: Some of the most severe human viral infections are spread by air.

Objective: This study tests the efficacy of barrier precautions by exposing human subjects to mono-dispersed live attenuated Influenza vaccine (LAIV) aerosols in droplet size.

Methods: Mono-dispersed LAIV particles were produced at 12.3 micron using a vibrating-orifice aerosol generator during 20 minute sessions in an air-tight chamber held constant at 22°C and 60%RH. Twenty four healthy, susceptible participants were exposed to the vaccine dosage and followed for 3 consecutive days. Participants were divided into 6 groups of 4: [1] no precautions; [2] trans-ocular transmission; [3] surgical mask without eye-protection; [4] surgical mask with non-vented eye-protection; [5] fit-tested N95 respirator w/o eye-protection; [6] fit-tested N95 respirator with eye-protection.  Outcome measure was virus detection in daily nasal washes by qRT-PCR.

Results: Influenza virus was detected immediately after exposure in 4/4 participants in group [1], 3/4 in group [2], 4/4 in group [3], 4/4 in group [4], 2/4 in group [5], and 1/4 in group [6]. No virus was found directly before and on days 2 and 3 after exposure.

Conclusions: Surprisingly, trans-ocular virus delivery occurred in most participants. Surgical masks did not prevent delivery of virus regardless of eye-protection. A fit-tested N95 respirator plus eye-protection prevented most, but not all, delivery.  None of the tested barrier precautions blocked Influenza completely. The lack of data regarding the human infectious dosage for Influenza limits interpretation of these data; however, the addition of eye-protection to the use of respirators may need to be considered.