Good to see that you are quoting reputable scientific journals, osris.
Your sources are reputable, however, I am not sure they are applicable to the coronavirus pandemic, as I will explain below.
Jacobs, J. L. et al. (2009) “Use of surgical face masks to reduce the incidence of the common cold among health care workers in Japan: A randomized controlled trial,” See: American Journal of Infection Control, Volume 37, Issue 5, 417 – 419. https://www.ncbi.nlm...pubmed/19216002
This study is not applicable to coronavirus transmission:
Pathogens can be divided into airborne and non-airborne types. Airborne means that small globules of respiratory secretions (saliva or mucus) containing the pathogen can float in the air for many minutes or hours and can infect people; whereas non-airborne means the pathogen may be ejected from a person's mouth or nose in a larger globule and infect people, but being heavier it quickly falls to the ground, and does not linger in the air.
Airborne globules can have a range of tens of meters; but heavier globules quickly fall to the floor within a meter or two (unless the person sneezes or coughs, in which case these heavier globules can get ejected across a longer distance).
Why are some pathogens airborne and others non-airborne?
Well, if a pathogens is very infectious even in tiny amounts, then even the small amounts contained in the smaller airborne globules are enough to seed a new infection when they enter an uninfected person's mouth or nose. Whereas if a pathogen in less infectious, then there may not be enough pathogen within these smaller airborne globules to seed a new infection, and in which case, the pathogen will not be transmitted via the airborne route. It is only the larger non-airborne globules that contain enough pathogen to seed a new infection.
Although it is suspected that some airborne transmission of coronavirus may occur, generally coronavirus is not considered a virus which normally transmits by the airborne route. As you know, coronavirus is also a common cold virus.
However, the most common type of cold virus is rhinovirus, and rhinovirus IS capable of airborne transmission (for a list of pathogens capable of airborne transmission, see here). Influenzavirus is also capable of airborne transmission. So this makes the regular rhinovirus cold virus different from coronavirus.
When a pathogen is airborne, surgical masks are not effective at stopping the virus from getting into your mouth or nose. So surgical masks will not be very effective at stopping rhinovirus or Influenzavirus.
This is because surgical masks are not fully sealed: they are not tight-fitting at the edges, so when you breathe in, air gets in unfiltered via the edges of the mask. So any rhinovirus or influenzavirus floating in the air will be able to get into your mouth via the edges of the mask.
This is probably why the study found surgical masks did not reduce the amount of colds, as rhinovirus is the most common cold virus.
The only masks that can fully stop airborne transmission are respirator masks, which are completely sealed at the edges. N95 and N99 specification masks (and their European equivalents FFP2 and FFP3) are examples of respirator masks. So you want respirator masks to stop airborne pathogens like rhinovirus and influenzavirus.
Surgical masks however can in theory be effective against coronavirus, because for the large part, coronavirus is not airborne, and so coronavirus usually gets into your mouth or nose only if you are standing close to a person, and some of their spittle globules are ballistically ejected from their mouth, and shoots in the direction of your mouth, like a bullet. A surgical mask placed either over your mouth or theirs will block this bullet.
And of course another route of coronavirus transmission is via contaminated hands: when you touch your mouth or nose with contaminated hands, the virus can get into your respiratory system and infect you. But again, a simple surgical mask or bandana stops you from touching your mouth and nose. So this is another way by which a mask use can prevent transmission.
It is also very important to note that most studies analyzing the effectiveness of masks only examine the case where masks are worn by the non-infected persons (eg doctors and nurses), to try to stop them from contracting pathogens from infected patients. The infected patients themselves do not wear masks.
But when we are talking about the general pubic wearing masks in this pandemic, in this case BOTH the infected person AND the person trying to protect themselves from infection are wearing masks (in places where mask use is mandated). This is significant firstly because it provides a double protection, but more importantly, because we know that masks are far more effective at stopping the infected person from ejecting globules of infected saliva in the first place, than they are at stopping the non-infected person from being exposed to those globules. So most of the benefit of mask use in the coronavirus pandemic will arise from the infected persons wearing a mask.
So if you are looking for studies which examine the efficacy of masks in stopping non-airborne pathogen spread in a pandemic, you need to find a study in which both the infected and non-infected people are wearing masks.
Edited by Hip, 19 July 2020 - 03:56 PM.