Previous studies have produced conflicting results on the importance of influenza virus transmission by airborne droplet nuclei. Human challenge-transmission studies have been proposed as a possible way to investigate this further. The authors randomly selected healthy, seronegative volunteers (donors, n = 52) for intranasal challenge with influenza A/H3N2/Wisconsin/67/2005. Recipients were randomised into an intervention group (n = 40) or control group (n = 35) and were exposed to donors for 4 days. Participants in the intervention group wore face shields and sanitised their hands frequently to limit large droplet and contact transmission. One transmitted infection was confirmed using serology in a control recipient, producing a secondary attack rate of 2.9% among controls and 0% in the intervention group. This is 1.3% overall, significantly less than the 16% expected based on a proof-of-concept study based on secondary attack rates.
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