Masks are an obvious barrier to droplets. Its inconceivable they would
do nothing. A good friend has told me that nothing I can say or show
him will make him change his mind that masks are effective. Such faith!
One of the 49 references listed sums up the problem and then tries to
resolve it by using mathematical models;
"The effectiveness of masks, however, is still under debate..... the
number of respiratory particles that may penetrate masks is substantial,
which is one of the main reasons for doubts about their efficacy in
preventing infections. Moreover, randomized clinical trials have shown
inconsistent or inconclusive results, with some studies reporting only a
marginal benefit or no effect of mask use. Thus, surgical and similar
masks are often considered to be ineffective. On the other hand,
observational data show that regions or facilities with a higher
percentage of the population wearing masks have better control of COVID-19"
Ill get to the modeling in a second.
The up do date observational studies seem to suggest no effectiveness.
The Centers for Disease Control says
“We did not find evidence that surgical-type face masks are effective in
reducing laboratory-confirmed influenza transmission, either when worn
by infected persons (source control) or by persons in the general
community to reduce their susceptibility.”
The World Health Organization says “At present, there is no direct
evidence (from studies on COVID-19 and in healthy people in the
community) on the effectiveness of universal masking of healthy people
in the community to prevent infection with respiratory viruses,
including COVID-19.”
Systemic Review by Cochrane says
“The pooled results of [67] randomised trials did not show a clear
reduction in respiratory viral infection with the use of
medical/surgical masks during seasonal influenza. There were no clear
differences between the use of medical/surgical masks compared with
N95/P2 respirators in healthcare workers when used in routine care to
reduce respiratory viral infection.”
So how did the Science article resolve the issue with modeling? They
determined that infection risk was not linear with mask effectiveness
but was determined by the concentration in the environment. They
concluded that masks may be effective in environments with low viral
concentrations and not effective in indoor, high viral locations. They
conclude that for masks to work, we should implement other things like
ventilation.
That raises the issue of environment. The vast majority of spread
occurs indoors, and in fact withing hospitals. Where we need the most
protection, the masks are not going to work, and where they may work, we
dont need them. Then at home, people just arent going to use them. So
there are many reasons why, contrary to our intuition, masks dont appear
effective in pandemics.
