Prevention

Physical distancing

As described in this web site’s sections “Saliva and mucous droplets” and “Aerosols,” larger droplets often fall from the air in one or two meters, and small aerosol particles can float for many meters.  So, the greater the distance you are from an infected person, the less likely that you will inhale many of their viruses (Anfinrud et al.; Asadi et al.; Bourouiba; Brosseau; Dhand, Li; Meselson; Tang, Li et al.; Stadnytskyi et al.).  A comparison of studies of the effects of physical distancing in household, community, and healthcare settings found that “at least 1 m physical distancing seem to be strongly associated with a large protective effect, and distances of 2 m could be more effective” (Chu et al.).

Face masks and shields

Masks reduce the numbers of aerosols and viruses going through them (Makison Booth et al.; Milton et al.).  Homemade fabric face masks reduce the distance droplets and aerosols spread from mouths (Rettner; Verma et al.).  Masks prevent some larger droplets and aerosols from being dispersed from the wearer to other people (Anfinrud et al.; Mueller, Fernandez).  Masks also prevent infected people from releasing respiratory viruses into the air (Leung et al.).  When COVID-19 infected hamsters were near other uninfected hamsters, and surgical mask material was placed between them, the other hamsters were infected less often and less seriously than when there was no mask (Chan JFW, Yuan et al.; Medical Xpress).

Masks also protect humans in society from COVID-19.  For example, two hair stylists with symptomatic COVID-19 infections worked with 139 clients in a salon, while both stylists and clients wore masks.  None of the clients, their contacts, and other stylists in the salon reported symptoms.  About half were tested, and all of those found negative (Hendrix et al.).  Retrospective studies showed that when the first infected case in a family wore a mask, they transmitted to other family members at less than half the rates of families in which the first case did not wear a mask (Hong L, Lin, et al.; Wang Y, Tian, et al.).  Masks were similarly effective protecting people from SARS-CoV-2, other coronaviruses, and influenza in community and healthcare situations (MacIntyre, Chughtai).  Even if the mask wearer gets infected, they inhaled a reduced number of viruses.  So, they are less likely to develop serious symptoms, and more likely to have mild or no symptoms (Gandhi et al.; Wu KJ.).

Since a large portion of infected people are asymptomatic or presymptomatic, if everyone wears a mask when near other people, they could prevent spreading these viruses to others.  If most people wore face masks in public, that would prevent some droplets and aerosols from an infected person reaching uninfected people, which could help reduce transmission, and show support for community pandemic responses (Cheng KK, Lam, et al.; Howard et al.; Royal Society).  A comparison of several studies of the effects of face mask use found that “…wearing face masks protects people (both health-care workers and the general public) against infection by these coronaviruses…” (Chu et al.).

So public health organizations recommended mask wearing (California; Centers for Disease Control and Prevention “Recommendations…”; National Academies of Sciences “Effectiveness…”; San Diego County).  Aerodynamics experiments found that the face mask materials with optimum balance of filtration and breathability were quilter’s cotton, silk, chiffon, flannel, denim, bed sheets, paper towel, canvas, and shop towel.  Higher density (thread count) fabrics filtered better.  Using layers of different materials filtered over 80% of aerosols, probably because of both mechanical filtering and electrostatic attraction (Konda et al; Robertson).

Experiments found that wearing clear face shields protects the wearer from droplets, especially the eyes, so experts recommended that people start wearing simple face shields when out in the community. Several companies sell them, and people can make and disinfect their own face shields (Bacher, Ianzito; Infectious Disease Society of America; Perencevich et al. including the comments).  A comparison of several studies of the effects of using them found “that eye protection could confer additional benefit” (Chu et al.).

If people used face masks, face shields, hygiene, and distancing, and changed their cultures to expect each other to maintain those norms, then they could greatly reduce community transmission (Gawande).  For example, circumscribed areas, traffic restrictions, home confinement, social distancing, centralized quarantine, and universal symptom survey probably contributed to decreases in infections and severe case rates in Wuhan, which provided an example of epidemic control methods people elsewhere used (Hartley & Perencevich; Pan A, Liu, et al.).