Avoiding pandemic situations

Under what circumstances are you likely to be infected by a Covid carrier? The advice has changed since last March when, lacking experience with the Covid virus, the experts were giving generic advice based on what was important for the yearly influenza virus. Ten months later, we know that half of new Covid infections come from asymptomatic “carriers” that temperature-taking misses, that most of the spread is via aerosol microdroplets rather than surface transfers, that preventing super-spreader events is an important strategy, and we accept family-sized pods as exceptions to the six-foot rule (shared responsibility to keep the others healthy). Here I distill such developments into identifying dangerous situations that can be avoided, plus a few instances where the rules of 2020 could be lightened.

As we shall see, it is important to avoid sporting events, where people behind you may shout for several hours. Noisy parties, bars, and school buses are even worse; on an airplane, while most people are not talking, they are trapped next to one another for much longer durations. But noisy restaurants combine all of the significant risk factors (distancing, ventilation, duration, loud speech, unmasked people nearby); they will need a low-noise redesign with higher air flow to get customers back.

Speech is an important way that viruses are packaged for export, as the shearing motion of the vocal cords serve to trap tiny air bubbles in the mucus, the essential setup for aerosol formation. When one begins speaking loudly, four times as many virus particles are emitted.

Second, while it may not protect you from other’s viruses very well, one must wear a face mask to avoid infecting others, just as surgeons do. The six-foot rule is all about protecting yourself from the larger droplets carrying thousands of virus particles; they do not hang around in the air in the manner of the invisible microdroplets. The larger droplets are heavy enough to settle to the floor before travelling more than six feet; however, in the little jets produced by violent sneezes, larger droplets can carry 25 feet. The smaller droplets that are slow to sink will soon evaporate their water content, popping the little air bubbles within the mucus containing the true aerosol virus particles. That’s nothing like the virus load of the larger containers — yet, over time, one can accumulate enough viruses to start an infection. So, keep moving.

What situations are setups for picking up a Covid infection?

  • When a carrier passes you when out walking? That’s a low possibility of infection, especially if outdoors in a breeze. But if the air is very still, you may encounter lingering pools of exhaled air where someone stood for a while, just as when you encounter the smell of cigarettes when there is no one around after a smoker’s break. Still, your passage is brief. You might inhale a few virus particles, but it likely takes hundreds to thousands to start an infection in your nose or eyes that can spread to the lungs and cause big trouble. You want to avoid situations where they can accumulate over an hour’s time.
  • Briefly talking to a carrier while your dogs greet each other? That’s usually not enough time, but the chances go up if the encounter is prolonged or if you begin shouting because of a noisy setting or move closer to hear one another. Back off if someone forgets.
  • Attending a meeting around a six-foot-wide conference table. Even with masks and six-foot spacing (not being able to pass a paper by touching a neighbor’s outstretched arm with yours), there is still elevated risk because of the need to raise your voice, to stay put for an hour, and inadequate ventilation when the door is closed. Stick to Zoom.
  • Those were also the risk factors responsible for one choir member being able to infect 53 others at a choir practice last March, despite no hugs and handshakes allowed.
  • In restaurants, people must take off their masks to eat. Noisy restaurants are even worse, as people lean closer together when they cannot hear well enough for conversation. Long group tables make people raise their voices, as does music, and so even couples at small tables soon have to shout.
  • Being a member of a mob is even worse than dining in a noisy restaurant. Jammed tightly together, mostly without masks except for press, people get in your face and shout. At least, should you catch the infection, the jail will provide medical attention at public expense.

Are there situations where the advice of last Spring now seems unwarranted? I can certainly see examples of where regulations could be cut back — for example, to allow outdoor Tai Chi classes with six-foot spacing. Family-sized pods really ought to be able to wander along the beaches or around art galleries if they distance from members of other pods (which means keeping a tight grip on children that wander), even though larger group activities with tight seating or school-bus transport continue to be banned. Occupancy limits and timed tickets might be needed.

Temperature-taking may still be needed, even though it will miss more than half of the carriers. Sometimes, even ineffective measures are warranted because they provide the concurrent ability to interview people, one by one.

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William H. Calvin

William H. Calvin

President, CO2Foundation.org. Professor emeritus, University of Washington School of Medicine in Seattle. Author, many books on brains, human evolution, climate