Those bulky N95 respirator masks may not be any better than regular surgical masks in preventing influenza transmission.
According to this JAMA study, 446 nurses were assigned to use either regular surgical masks or the N95 respirator masks when caring for febrile patients with respiratory illnesses during the 2008-2009 influenza season. Of those nurses, 50 using plain surgical masks became infected with influenza and 48 using the N95 respirator masks became infected with influenza – a result that did not reach statistical significance.
Another interesting statistic in the study – roughly 70% of nurses who had influenza diagnosed by serology had no symptoms.
Not only does this study show that plain surgical masks and N95 masks are comparable in flu prevention, but it also shows the significant risk health care workers encounter when caring for patients with influenza like illnesses. Out of 446 nurses, 98 got influenza even when using masks. That’s a 22% transmission rate with mask use. According to this article in Science, transmissibility of influenza is estimated to be 27.3% without mask use. Based on these studies (and I haven’t done exhaustive research for others), the effectiveness of masks seems to make only a modest difference in reduction of influenza transmission.
The Science study showed that the largest factor in reducing transmission of influenza throughout the population was … immunization. According to the article, reaching 70% immunization, plus immunization of the high risk groups such as health care workers could avert a pandemic.
I have heard of several hospitals that require non-immunized staff to use N95 masks at all times during work hours.
The JAMA study made me wonder whether such a policy uses the masks like “nag screens” with computer programs: The masks may not affect influenza transmission that much, but they encourage workers to get immunized … just so they don’t have to keep wearing the masks.