Efficacy of various types of masks
With the possibility of airborne transmission of the virus, are cloth masks as recommended by the CDC truly helpful in preventing infection? A study in the Journal of Medical Virology demonstrates 99.98%, 97.14%, and 95.15% efficacy for N95, surgical, and homemade masks, respectively, in blocking the avian influenza virus (comparable to coronavirus in size and physical characteristics). The homemade mask was created using one layer of polyester cloth and a four-layered kitchen filter paper.13
N95 masks (equivalent to FFP/P2 in European countries) are made of electrostatically charged polypropylene microfibers designed to filter particles measuring 100-300nm in diameter with 95% efficacy. A single SARS-CoV-2 molecule measures 125 nm approximately. N99 (FFP3) and N100 (P3) masks are also available, though not as widely used, with 99% and 99.7% efficacy respectively for the same size range. Though cloth masks are the clear-cut last resort for medical professionals, a few studies state no clinically proven difference in protection between surgical masks and N95 respirators.14,15 Even aerosolized droplets (< 5 mcm) were found to be blocked by surgical masks in a Nature Medicine study in which 4/10 subjects tested positive for coronavirus in exhaled breath samples without masks and 0/10 subjects with masks.16
On the contrary, an Annals of Internal Medicine study of four COVID-19 positive subjects that “neither surgical masks nor cloth masks effectively filtered SARS-CoV-2 during coughs of infected patients.” In fact, more contamination was found on the outer surface of the masks when compared to the inner surface, probably owing to the masks’ aerodynamic properties.17 Because of limitations present in the above-mentioned studies, further research is necessary to conclusively determine which types of masks are efficacious in preventing infection by the virus. In a scarcity of surgical masks and respirators for health care personnel, suboptimal masks can be of some use provided there is adherent use, minimal donning and doffing, and it is to be accompanied by adequate hand washing practices.14
In case of severe infections with high viral loads or patients undergoing aerosol-generating procedures, powered air-purifying respirators (PAPRs) also are advisable as they confer greater protection than N95 respirators, according to a study in the Annals of Work Exposures and Health. Despite being more comfortable for long-term use and accommodative of facial hair, their use is limited because of high cost and difficult maintenance.18 3-D printing also is being used to combat the current shortage of masks worldwide. However, a study from the International Journal of Oral & Maxillofacial Surgery reported that virologic testing for leakage between the two reusable components and contamination of the components themselves after one or multiple disinfection cycles is essential before application in real-life situations.19
Ongoing issues
WHO estimates a monthly requirement of nearly 90 million masks exclusively for health care workers to protect themselves against COVID-19.20 In spite of increasing the production rate by 40%, if the general public hoards masks and respirators, the results could be disastrous. Personal protective equipment is currently at 100 times the usual demand and 20 times the usual cost, with stocks backlogged by 4-6 months. The appropriate order of priority in distribution to health care professionals first, followed by those caring for infected patients is critical.20 In a survey conducted by the Association for Professionals in Infection Control and Epidemiology, results revealed that 48% of the U.S. health care facilities that responded were either out or nearly out of respirators as of March 25. 21