World Health Organization (WHO) Writing Groupは『Nonpharmaceutical Interventions for Pandemic Influenza: Transmission Characteristics
of Influenza Viruses（アクセスには会員登録が必要）』は、
「evidence for aerosol spread (especially in unventilated conditions) is
available」
と、空気感染するという証拠があることは認めているが、
「Data do not exist to quantify the relative efficacy of surgical masks versus respirators in preventing influenza infections in exposed persons, but surgical masks should protect against large droplets, believed to be the major mode of transmission.」
と、サージカルマスクが、インフルエンザ感染の防止において、N95マスクに劣るというデータはないと述べている。
以下、『Nonpharmaceutical Interventions for Pandemic Influenza: Transmission
Characteristics of Influenza Viruses』から関連部分を抜粋。
Large-Droplet and Aerosol Respiratory Transmission
Animal studies and most influenza outbreaks among humans suggest that virus-laden
large droplets (particles >5 mm in diameter) generated when infected
persons cough or sneeze are the predominant mechanism of influenza virus
transmission.[8]However, evidence for aerosol spread (especially in unventilated
conditions) is available.[9]Although a direct comparison has not been made,
experimental studies suggest that the infectious dose for humans exposed
by aerosol is lower than that seen with experimental nasopharyngeal instillation.[10]
The precise proportion of infections transmitted by large droplets versus
aerosols is difficult to assess and likely depends on the setting but is
relevant when developing recommendations on mask use. Data do not exist
to quantify the relative efficacy of surgical masks versus respirators
in preventing influenza infections in exposed persons, but surgical masks
should protect against large droplets, believed to be the major mode of
transmission.
[8]Bridges CB, Kuehnert MJ, Hall CB. Transmission of influenza: implications for control in health care settings. Clin Infect Dis. 2003;37:1094-101.
[9]Moser MR, Bender TR, Margolis HS, Noble GR, Kendal AP, Ritter DG. An outbreak of influenza aboard a commercial airliner. Am J Epidemiol. 1979;110:1-6.
[10]Alford RH, Kasel JA, Gerone PJ, Knight V. Human influenza resulting from aerosol inhalation. Proc Soc Exp Biol Med. 1966;122:800-4.