Personal COVID Risk
The other day I heard my parents arguing about whether or not it was safe to go to the grocery store:
- Mom: It’s very dangerous. People are dying.
- Dad: It’s completely safe. I wear a mask and keep distance.
In truth, going to the store is neither very dangerous, nor completely safe. It’s somewhere in the middle. But where?
After speaking with my parents for a while I learned that they didn’t have a good mental model on how to think about quantitative risk. This post is for them. This post estimates the probability that an individual contracts COVID before they get a vaccine using rough facts and back-of-the envelope calculations. To be specific, this post uses my parents, who are in their seventies and live in Southern California.
Disclaimer: I am not a medical professional. I encourage you to get actual medical advice from established medical authorities, like the CDC and WHO. I’m just a crank on the internet with a blog.
Very roughly, I suspect that my parents are about 10% likely to contract COVID before getting vaccinated if they behave like everyone else. I’m probably about 20% likely.
Today the US sees around 300,000 cases per day, with a population 1000 times greater, at about 300,000,000
So waking up each day, an American resident has about a 1 in 1000 chance of learning that they have COVID.
If they wake up ten days in a row, they have about at 1 in 100 or 1% chance of learning that they have COVID
California is a hotspot in the country currently, and LA is a hotspot within California.
Without checking numbers, I’m going to guess that this makes one about 2x more likely to get COVID on a day-by-day basis
My parents are older (sorry folks) and, like most people their age, have various health issues. They’re likely to be early in line for a vaccine, but not first. Given logistical difficulties I suspect that they’ll get a vaccine some time in March, about 50 days from now
So 1 in 500 chance of waking up with COVID every day for Californians
x 50 days until vaccination
results in a 1 in 10 chance of contracting COVID prior to receiving a vaccine in March
if they act like their friends and neighbors
As a relatively healthy relatively young person, I’m probably closer to 1 in 5 (20%) due to getting a vaccine a bit later in the year.
Remember that I am just a crank on the internet. Please take this post more as an exercise for how to approximate risk, rather than as an actual estimate of that risk.
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