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Simulation: Early Adoption of Masks Will Protect You, and Others Too

Simulation: Early Adoption of Masks Will Protect You, and Others Too

Photo: Anna Shvets/Pexels.

As the Government of India relaxes its lockdown, intended to slow the spread of the novel coronavirus, one thing is certain: the pandemic itself is far from over. We all will have to begin going about our daily lives, and while we do so, we must understand that there are several measures at our disposal to protect ourselves, our families and ultimately our society from this pandemic. These are already very well-known by now. Maintaining physical distancing from others (at least 1 metre), washing hands with soap frequently or using sanitiser when soaps are not immediately available, learning to not touch one’s face (especially, nose, mouth and eyes) and wearing masks in public.

Of these, however, we believe the messaging regarding wearing masks seems to have been mixed at best and confusing at worst.

During the initial stages of the pandemic, the WHO did not endorse the use of face-masks by the general public for protection from the novel coronavirus. Dr Michael Ryan, the executive director of the WHO Health Emergencies Programme, went so far as to say, “We don’t generally recommend the wearing of masks in public by otherwise well individuals because it has not up to now been associated with any particular benefit.”

Part of this had to do with the circumstances  prevailing at that time. The reasons included short supply of masks, false sense of security and no clear indication that masks really protect us. WHO subsequently back-pedalled a bit; on April 6, it released a statement saying, “The use of masks made of other materials (e.g., cotton fabric), also known as non-medical masks, in the community setting has not been well evaluated. There is no current evidence to make a recommendation for or against their use in this setting.”

On June 6, WHO made a U-turn and has since advised everyone to wear masks in public.

Even before the latest recommendation from WHO, there was evidence building that regions across the world where mask use was common were reporting significantly fewer COVID-19 numbers. Given this, countries that did not recommend mask usage by the general public earlier have turned around and strongly recommended the use of non-surgical masks. For example, the US Centers for Disease Control (CDC), after vacillating for several months on this issue, issued the following recommendation: “CDC is additionally advising the use of simple cloth face coverings to slow the spread of the virus and help people who may have the virus and do not know it from transmitting it to others”.

Indian government agencies, including the Indian Council for Medical Research and the Office of the Principal Scientific Advisor, have issued strong messages promoting the use of homemade masks by the people at large. We are gladdened by the fact that Prime Minister Narendra Modi and several elected officials have on many occasions emphasised this and have appeared in public with masks, imparting a strong message. There is also sufficient scientific evidence from several countries emphasising the fact that masks do help us in this pandemic. People in our country seem to have embraced these messages well, at least for now.

Also read: The Effect of Using Face-Masks and Other Protection on COVID-19 Transmission

As part of our efforts to understand the progression of this pandemic, we are involved with two colleagues in conducting an online survey on social distancing efforts in our country (the survey is still ongoing). The maximum responses we received was during the third phase of the lockdown: it was quite striking that 84% of the approximately 2,600 respondents noted that at least half the people in their neighbourhoods wore masks.

Workplaces that continued to stay open during the lockdown have been advised to make masks mandatory. In spite of all these efforts, there is a real danger of this compliance waning as time passes. It’s important to constantly reinforce that widespread mask use can stem the spread of the novel coronavirus and save lives, especially when combined with physical distancing and good hand-hygiene.

A lot has been said on these pages and elsewhere about the importance of wearing masks. Our goal in this article is to show with a computer simulation that mass mask use can lower the number of infections in a community. The simulation was inspired by a simulator published in the The Washington Post on March 14.

When a large number of people start wearing masks early enough in a pandemic, it has a positive effect in reducing the number of infections. In our simulations, we have a population of 100 individuals each independently on a random ‘walk’. There is one infected individual, the red dot, and the remaining 99 uninfected individuals are indicated by green dots. An individual becomes infected with 100% probability if they come within 0.3 metres of an infected individual.

We let the simulation run for a certain number of time-frames, after which 50% of the individuals (infected and uninfected) wear masks. Masked individuals are indicated by a cross (‘×’).

There are four scenarios as a result. The specific probabilities in the last three scenarios are motivated by the results of a research paper published on April 21.

1. When a non-masked infected individual approaches a non-masked uninfected individual, there is a 100% probability of catching the infection. This is the case when a red dot approaches a green dot.

2. When a masked uninfected individual approaches a non-masked infected individual, there is a 50% probability that the masked individual catches the infection. This is the situation when a green cross approaches a red dot.

3. When a masked infected individual approaches a non-masked uninfected individual, there is a 33% probability that the non-masked individual catches the infection. This is the situation when a red cross approaches a green dot.

4. When a masked infected individual approaches a masked uninfected individual, there is a 25% probability that the masked uninfected individual catches the infection. This is the situation when a red cross approaches a green cross.

We developed two simulations where individuals start at the same locations and make identical random walks. The one in the first video below (‘Video 1’) corresponds to the situation when 50% of the individuals start wearing masks after 25 time-frames (early mask adoption), and the one in the second video below (‘Video 2’) corresponds to that after 75 time-frames (late mask adoption).

The Python code for the simulations is available on Github.

The upper simulation in both videos above describes a scenario wherein none of the individuals wear masks, and the bottom simulation describes the situation when 50% wear masks after 25 and 75 time-frames, respectively. Both simulations now run for a total of 300 time-frames.

The graph on the right side of each simulation describes the number of infected individuals in these two situations. As can be seen, even with 50% mask usage, there is a positive effect on the total number of infections in a community. When combined with physical distancing measures and other hygiene practices, we can expect significant reduction in the number of infections. Of crucial importance is the need for people to start wearing masks early on in a pandemic.

This motivated us to describe different scenarios: when people begin wearing masks after 25 and 75 time-frames. As the reader can observe from the graph in video 2, introduction of masks later on in the simulation has only a minimal effect in reducing the number of infections. As of publishing this article, the total number of known COVID-19 infections in our country stood at 3.54 lakh. This constitutes approximately 0.023% of our total population. While we still have time, it is important to continuously reinforce the importance of wearing masks in our fight against this pandemic.

Also watch: How to Wear and Remove a Mask Properly

In summary, we strongly feel that periodic messaging reinforcing mask usage in public is required. Our elected officials and public figures, including celebrities, should take the lead in this messaging. The government should also seriously consider handing out reusable cloth masks, soaps and sanitisers along with food rations to the poorest sections of our society. Mask use in significant numbers by the people will save us, our family and ultimately our society from the worst of this pandemic.

Venkateswaran P. Krishnan is an associate professor at the TIFR Centre for Applicable Mathematics, Bengaluru. Subhashini Sadasivam is chief scientific officer at DeepSeeq Bioinformatics LLP. The views here are personal.

Note: This article was edited at 12:50 pm on June 20, 2020, to share the link to the simulation’s code.

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