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Highlights of the article
- Face covering reduces risk rather than absolute prevention
- Limitations of face masks
- Face masks coupled with other measures are ideal for curbing Covid-19
Soon after the WHO declared COVID-19 as a pandemic, various mitigation measures have been implemented by many countries to constrain the pandemic, including widely adopted social distancing, home isolation, hand sanitization, and mandated face coverings. The scientific data detailing their effectiveness individually or combined is still limited. Notably, face masks have been a matter of intense debate during the COVID-19 pandemic. Early on, several government officials and health authorities were discouraging healthy people from wearing masks because of the fact that there was little evidence showing its ability to prevent spread among people. Regardless of the debates in the medical community, more and more countries are moving forward with recommendations or mandates to wear masks in public.
Curbing the COVID-19 fatality relies on the scientific understanding of the virus transmission routes, which determines the effectiveness of the mitigation measures. Face covering can prevent viral transmission and reduce the risk of infection by the following three ways: it can (1) block the rapid turbulent jets generated while coughing/sneezing, (2) filter virus particles such as aerosols or droplets, and (3) prevent inhalation of virus-bearing aerosols.
Do we have any evidence supporting the effectiveness of masks?
A growing body of research supports the use of different types of masks, though the quality of evidence varies. In a recent study, Zhang and co-workers analyzed the trend and mitigation measures in China, Italy, and New York City, from January 23 to May 9, 2020. The authors demonstrated that with social distancing, quarantine, and isolation in place worldwide and in the United States since the beginning of April 2020, airborne transmission represents the only viable route for spreading the disease, when mandated face coverings are not implemented.
In an experiment using high-speed video, it was shown that while speaking simple phrases hundreds of droplets ranging from 20 to 500 micrometers were generated. But when the mouth was covered by a damp washcloth nearly all these droplets were blocked.
Another study published in The Lancet systemically assessed 172 observational studies, looking at the effect of different mitigation measures such as physical distancing, face masks, and eye protection on the transmission of Covid-19. The N95 masks were found to offer 96% protection from infection whereas surgical masks (or comparable reusable masks) were 67 percent protective.
In another compelling case report, face mask has been shown to prevent Covid-19 transmission on an international flight. A Covid-19 positive passenger flew from China to Toronto. He wore a mask on the flight and all the other 25 passengers close to him on the flight-tested negative for Covid-19.
There are other reports too supporting the efficacy of masks.
Does face mask have any limitation?
Yes. There are few rising concerns with the use of face masks as many think that covering the face fails to recognize several important facts such as:
- The filter performance of a cloth material varies and does not necessarily represent its performance
- Transmission of a disease is much more intricate than merely a short interaction between people. Transmission of a disease relates to particulate matter concentration in the air and the duration of time exposed to that concentration
- Very small size particles of aerodynamic diameter ≤1µm escape easily from cloth mask
- Face mask does not eliminate the risk of catching infection through the membranes in your eyes
Owing to such concerns, it can be speculated (not concluded) that face covering offer many benefits but also has certain limitations. Therefore, face masks offer have limited impact on lowering COVID-19 transmission, and caution should be given while considering them as a replacement for physical distancing or self isolation.
Do we need to wear masks, if we’re practicing social distancing?
Yes.
The other advocated mitigation measures such as physical distancing are equally important and are beneficial in preventing direct contact transmission but owing to rapid air mixing, it itself is insufficient without face masks to protect the inhalation of virus-bearing aerosols/small droplets at intermediate proximity.
Take home message
Consider this example: We do physical exercise not because it is going to prevent us from getting a heart attack, but by doing so we are reducing our risk of getting it.
Similarly, face masks in compliance with hand hygiene, physical distancing, and other infection preventions and control measures are critical to prevent transmission of COVID-19. Recent studies suggest that timely and comprehensive mitigation measures are needed to prevent a second wave of COVID-19.
