Research has shown that most of the tiny droplets, invisible to the naked eye, known as aerosols, emitted when somebody coughs, or sneezes are trapped by a mask. This means that when a person infected with the coronavirus sneezes, a mask protects those around that person from inhaling those droplets, which contain the virus particles.
The most effective mask is the one known as N95. It is the mask worn by health professionals who handle patients sick with Covid-19. They can stop the tiniest droplets as small as three microns (micron is a fraction of 1 million of a metre). They stop 95 percent of all particles from getting through to the wearer’s mouth or nose. However, N95 masks are in short supply globally, so they cannot be worn by the public. The other alternative is surgical masks. Whichever mask one wears, it should be close enough to your face that most of the airflow is going through the mask. All masks prevent tiny breath droplets from flying out of the wearer’s mouth when they sneeze or cough. Therefore, any mask is better than no mask at all.
Scientists say that masks are best at protecting others than at protecting the wearer, hence the popular saying: Your mask protects me, and my mask protects you”. N95 masks, which are the most effective stop 95 percent of particles from reaching the wearer. Surgical masks stop at least most droplets from escaping into the immediate environment and from flying more than one and a half metres from the wearer. Even aerosols from a sneeze cannot fly more than 1.5 metres from the wearer.
According to information issued by the United States Centres for Disease Control and Prevention (CDC), one needs to inhale 1000 virus particles to get infected by the coronavirus. The following are the estimated number of particles emitted by different breathing activities.
• Normal breathing: 20 virus particles
• Speaking: 20 virus particles
• Cough: 200 million virus particles (Many of these remain in the air for hours in poorly ventilated environments)
• Sneeze: 200 million virus particles
There is still one aspect of prevention that has not received enough attention – time over which you remain exposed to infectious particles in the air. Growing evidence is showing that Covid-19 infection, like other illness us related to prolonged time of exposure. The higher you stay in an environment that may contain the virus, the higher the risk of getting sick. An expert named Erin Bromage from the University of Massachusetts Dartmouth, in May 2020 shared a simple formula to illustrate this. Successful infection = exposure to virus x time.
If you are in an environment where there is a high concentration of viral particles in the air, such as poorly ventilated closed spaces, you are most likely to get infected, but only if you stay there for a long time.
One important aspect of protecting yourself from infection by the coronavirus is the amount of virus particles hanging in the air where you are. Moving air causes invincible droplets containing the virus to be easily blown away in a short time. The opposite is true about poorly ventilated closed areas. People who stay for long hours in poorly ventilated closed areas are more likely to get infected. They breath in more infected particles and they do so for a long time. In restaurants for example, it is best to stay outdoors whenever possible. If this is not possible, choose a table next to a window and ensure that the window remains open.
The scientists who has taken the frontline in emphasising the importance of time as an important factor in Covid-19 spread, Erin Bromage from the University of Massachusetts Dartmouth, says that his formula suggests that short trip to the supermarket comes with lower risks. However, employees in those supermarkets who do eight-hour shifts have a higher risk. “Even if there is a virus in that environment, you hopefully have not had extended time needed to get an infectious dose. The employees though are in that environment all day. So, what did not infect you because t did not get to the infectious dose number, has a much stronger effect or larger effect on an employee that gets a low dose all day,” he explains.
Therefore, an infected person who attended a choir practice in Washington State on March 10, 2020 caused the infection of 53 out of 61 people who attended the event, which was 87 percent. No one reported physical contact with the person, but all sat close together. The research by Bromage concludes that louder places where people shout such as bars are riskier to spend extended time in, when there is an infected person than quieter places. Infected people talking loudly emit more infectious droplets than those in environments where people talk normally.
