Living is dangerous. There are risks to life and limb all around each of us. Many times we don’t appreciate or can’t even see the threats around us. For example, the current COVID-19 crisis and ongoing and accelerating climate crisis are both caused by invisible culprits that can be seen only using an electron microscope (coronavirus) or an infrared FLIR camera (greenhouse gases). But not being able to see them doesn’t mean those threats don’t exist, and so we try to find ways to protect ourselves and loved ones from harm.
Taking one precautionary action may reduce the risks surrounding us to some degree, but as Dr. Peter Tippett explains by using the example of passenger safety, using several actions at once provides layers of protection that reduces risk even more:
All protections or countermeasures are only partially effective. For example, wearing the seat belt in your car reduces the likelihood of dying by about 50% compared with not wearing it. You can think about that as horrible (“it will fail half the time!”), or as great (“it cuts the risk of dying in half!”). For everything we care about, in all aspects of life, we solve this “risk” problem by using countermeasures together to improve their collective effectiveness. Independently, air bags reduce the risk of dying by about 30-40%. When added together with seatbelts, they are synergistic and reduce risk together by 65-70%. We add licensing, speed limits, anti-lock brakes, police enforcement and other things to achieve very good risk reduction (well into the upper 90s). We need to be even more careful when we drive in more dangerous situations, such as in a snowstorm. Protecting yourself (and society) from COVID works exactly the same way—you just can’t see the snow.
Here’s how the combination of wearing a mask and social distancing reduces the risk of contracting respiratory viruses:
Your nose reduces the risk of viral particles getting to your throat. A mask reduces the risk of the viral particles getting to your nose, and social distancing reduces the risk of them getting to your mask. Together, these countermeasures work very well.
Dr. Tippett does the math for us to show the relative value of adding layers of protection:
If your nose reduces the risk by 80% […], and a mask by another 80% and the six-foot distance by 80% more, then collectively, the failure rate would be (0.2*0.2*0.2 = .008) = 0.8%. In other words, the collection of countermeasures would be (1 minus the failure rate) = over 99% effective in reducing your chances of getting sick. In this example, any two together would be 96% effective and any one alone would be 80% effective.
So based on this example calculation, if you are standing with your mouth closed and normally breathing close to a COVID carrier as they are speaking to you, you may have a 20% chance of getting sick from that exposure. Add a mask and that would go down to 4%, add distance and that goes to under 1%. Add repeated individual exposures from other people, and your risk gets worse. Add more countermeasures and your safety improves. The power of each individual countermeasure is much less important than their collective power in protecting you.
The article provides lessons in how viruses replicate once inside a human cell, and how they die once expelled to the outside world (they do both very quickly). Dr. Tippett reviews the benefits of keeping the hands clean with soap and water and hand sanitizers, and surfaces clean with disinfectants. Six feet is the recommended distance apart, but 10 feet is better. As for masks and gloves, here’s the bottom line:
• Wear a mask when you are in “exposure” zones (mainly places with other people).
• Treat your home, car, and yard as safe places (no mask or gloves).
• Be on high alert on what you are doing with your hands when you are in “danger zones.” This is when you must not touch your face.
• Consider wearing gloves (even winter gloves or work gloves can be helpful) but only for short periods of time and only when in “touch exposure” danger zones.
• Remove your gloves (and mask) when you return to your safe place.
• Wash your hands every single time you take off your gloves or mask or move from a danger zone back to a safe zone.
• When you are at home and after washing up, you can relax, scratch your nose, rub your eyes and floss your teeth…without worry.
The Commonwealth of Pennsylvania has comprehensive information on COVID-19 on their website here.
(Back pat: John Duffy)
(Photo: Dr. Brian Donnelly, AHN Pediatrics – Pediatric Alliance Wexford)