Will face masks protect me from COVID-19?

Even if you’re asymptomatic, face masks will protect you and others from COVID-19.

Data supports the important role of face coverings, even cloth ones, in preventing COVID-19 spread. This is all the more important because of the high risk of asymptomatic transmission of COVID-19.

The confusion around a statement from WHO

Last week the WHO’s technical COVID-19 response leader, Dr. Maria van Kerkhove, used the words “very rare” to describe asymptomatic transmission of COVID-19. Her statement suggested that face masks were not necessary for those presenting no COVID-19 symptoms. This caused much confusion, particularly during our vulnerable stages of re-opening. The following day, Dr. van Kerkhove clarified that she was only referring to “a small subset of studies” that specifically investigated asymptomatic transmission, and that she was not “stating a policy of WHO”.

“It is a misunderstanding to state that asymptomatic transmission globally is very rare”

Dr. Maria Van Kerkhove (technical lead of WHO’s COVID-19 response)

So to be clear, the WHO recommends wearing cloth face masks or coverings because of the large rate of asymptomatic spread.

In addition to providing more clarity on this misunderstood statement, I also wanted to share the latest data behind the effectiveness of mask usage:

  • Reviewing the COVID-19 outbreak aboard the USS Theodore Roosevelt notably showed ~20% were asymptomatic and lower odds of infection in:
    • Those using face coverings (55% vs 80%),
    • Avoiding common areas (53% vs 67%), and
    • Observing distancing (55% vs 70%).
  • U.S. Air Force Basic Military Trainees: this high risk group of individuals demonstrated significant success at limiting COVID-19 spread from a small number of index cases. The following guidelines protected ~10,500 trainees who developed only 5 symptomatic COVID-19 cases and 3 transmissions:
    • Arrival quarantine,
    • Distancing,
    • Cloth face coverings,
    • Rapid isolation.
What is already known about this topic?

Substantial COVID-19 transmission has been documented in some congregate living settings.

What is added by this report?

Nonpharmaceutical interventions (NPI) introduced among 10,579 basic trainees at Joint Base San Antonio-Lackland limited COVID-19 incidence to five cases (47 per 100,000 persons), three of which were in persons who were contacts of the first patient.

What are the implications for public health practice?

Despite documented outbreaks of COVID-19 in congregate settings, implementation of NPIs, including screening, testing, administrative measures, quarantine, isolation, and source control, can limit transmission of symptomatic COVID-19 and ensure continuity of critical activities.
  • Conservative modeling of face mask effectiveness suggests impressive results. When facemasks are used by the public all the time (not just when symptomatic), the effective reproduction number can be decreased below 1. This is even assuming a modest 50% effectiveness of masks capturing exhaled virus when combined with periods of lockdown and distancing.
    • Decreasing the reproduction number to below 1 is significant as it provides potential to control epidemic spread.
    • Effectiveness of simple face masks in reducing droplet and aerosol spread is likely higher than 50%.

Our modelling analyses”provide support for the immediate, universal adoption of facemasks by the public.”

Stutt et al. University of Cambridge

Our conclusion is to continue wearing face coverings (safely and correctly!) when in public, particularly in enclosed spaces.

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The information provided in this post in intended for general education. It is not medical advice. While I make every effort to provide the most up-to-date information, please note that new data is continuously becoming available and may change the conclusions I present here.

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