EDITOR:

This letter is regarding Ralph Blasier’s letter “Mask Facts (COVID 19)” and “Mask facts two, COVID”, and specifically concerns the study Mr. Blasier cited that was conducted by “faculty of the School of Public Health and Community Medicine, University of New South Wales, Sydney Australia” (titled “A cluster randomized trial of cloth masks compared with medical masks in healthcare workers” published in BMJ Open in April of 2015). The study itself was conducted across 14 hospitals in Hanoi, Vietnam with participants being monitored for a total of five weeks beginning in March of 2011. Therefore, this study took place eight years prior to the emergence of COVID 19. In Mr. Blasier’s letter “Mask facts two, COVID”, he writes “In this study cloth masks did not reduce the spread of COVID”, which is misleading given that COVID 19 was not a respiratory virus in existence at that time. However, the study did monitor other respiratory viruses with varying degrees of transmissibility (such as RSV, influenza strains, and other pre-COVID-19 coronaviruses).

At first glance, a person may assume that this study’s results (which indicated the “cloth mask” group was not as effective as the “usual practice” group or “medical mask” group at reducing illness) may also be reasonably applied in the current pandemic. However, it is important to point out that the “usual practice” group in this study still wore masks when the health care worker deemed it medically necessary (e.g., meeting with a symptomatic patient) and therefore was not a true “no mask” control group. The other point worth noting is that this study took place within healthcare settings where infectious individuals concentrated and were not required to mask at that time, rendering the cloth mask of the health care worker less protective regardless.

The lead author (Chandini Raina MacIntyre) of this study cited by Mr. Blasier performed a post hoc analysis on a subset of their original data in a 2020 paper published in BMJ Open and found there was no significant difference in infection rates between health care workers who wore cloth masks washed in the hospital laundry compared with medical masks, but that those health care workers who hand washed their cloth masks had more than double the risk of respiratory illness by comparison. The study’s authors conclude “A well-washed cloth mask can be as protective as a medical mask”.

Natalie Randall

Escanaba