The CDC Can’t Tell You What You Want

Pandemic risk assessments are never truly objective, because one of the variables is you.

Cheering, unmasked fans on one side and a lonely masked fan on the other.
Tomazl / Getty; Mike Kireev / NurPhoto / Getty

About the author: Jordan Ellenberg is the John D. MacArthur Professor of mathematics at the University of Wisconsin at Madison and the author of Shape: The Hidden Geometry of Information, Biology, Strategy, Democracy, and Everything Else.

More than six weeks ago, I received my second Moderna shot, so I’ve had time to ease into fully vaccinated life. And yet I still haven’t eaten a meal inside a restaurant. Is that because I’m an overcautious ninny who can’t estimate risk? Bent into a defensive trauma crouch from a year of COVID-19 restrictions? Or worried I’ll shed some stray mRNA and disrupt the menses of surrounding diners?

No. It’s because I live in Wisconsin. And it’s May. This is my chance to sit and eat alfresco during the short segment of the year when neither snow nor a hornet is likely to drop into my bowl. Skipping the dining room is a minuscule sacrifice for me—so small that it’s outweighed by the also-minuscule chance of my catching or passing along the coronavirus.

Because I’m a mathematician, friends often ask me what’s okay for them to do in this stage of the pandemic. I can help them understand the statistical evidence, but what I can’t do—what no one, not even the CDC, can do—is tell them what they want, or how much they want it. Truly universal advice is impossible, and decisions about risk are always subjective, because one of the variables is you.

Large-scale trials suggest that fully vaccinated people like me enjoy something like a 20-fold reduction in risk of contracting symptomatic COVID-19, at least with the Pfizer and Moderna vaccines. Better still, the CDC in late April reported only about 10,000 “breakthrough cases” out of the first 95 million Americans vaccinated, a one-in-10,000 fraction—though you have to figure that most vaccinated people aren’t taking COVID-19 tests, so the amount of infection and potential transmission among the vaccinated is presumably higher than the official number. (“It is important to note that reported vaccine breakthrough cases will represent an undercount,” as the CDC soberly put it.)

All these numbers have huge error bars around them. And what that 20-fold reduction really means depends, to some extent, on who you are. Although a vaccinated 75-year-old and a vaccinated 25-year-old pose roughly the same (minor) threat to public health, being out in the world might pose a greater danger to the senior citizen.

The fact is, binary classifications such as “safe” and “not safe” mostly don’t exist in real life, and those who seek them may well be led astray. No government agency or Anthony Fauci lieutenant ever said you can’t catch the coronavirus from six feet and one inch away—six feet was always an arbitrary “good enough” standard established so that the grocery stores knew how far apart to put the shoe stickers on the floor. But many people nonetheless experienced the recommendation as a sharp-edged boundary: danger within the six-foot circle, safety outside. This kind of all-or-nothing thinking reached its absurd climax in high schools in Billings, Montana, last October. Responding to guidance that coronavirus transmission was a danger when students spent at least 15 minutes within six feet of one another, the schools introduced a new mitigation strategy: Everybody changes desks every 14 minutes.

Even if the CDC could offer more precise individualized assessments, it certainly couldn’t provide an objective answer to what activities you personally should embrace or avoid. The CDC is not a health-care adviser. Its mission, just like it says on the can, is to control disease, and its recommendations are issued with that goal in mind. Roughly speaking: If a choice is safe enough that the whole country can make it without causing COVID-19 case rates to skyrocket, it gets the green light.

These green lights simply can’t take into account that every decision we make is a trade-off between a risk (to ourselves and others) and a benefit (ditto), and we balance the two. Should I eat inside the restaurant? It depends on how much it bugs me not to. Should you get on that plane? It depends on the level of public-health risk you impose on the population by boarding the plane, which the CDC can help you figure out, but also on how eager you are to see the person or place on the other end of the flight—and that’s purely up to you. (I’m flying to see my parents next month.)

My son has been going to school in person for a month now. But about a third of his high school isn’t there. Maybe the absent students and their parents have a different view than my wife and I do about the danger of transmission between unvaccinated teenagers in a classroom with everyone masked and overhauled air filtration. Or maybe those families are just less troubled than others by school on a screen.

In a year when so many of us have been peevishly scolded to “follow the science”— seemingly no matter what we do—paying attention to what we actually want can seem irresponsibly unscientific and nonobjective. No! What’s unscientific is treating a trade-off as if it had only one side just because we can measure only one side numerically. People are different from one another, not just in our age and immune robustness, but in our desires and our needs. The past year has helped a lot of us figure out which things we really mind giving up—and, in some cases, which things we’ve found we like giving up.

The question is not what’s safe (nothing is completely safe!) or what’s safe enough—the question is, among those things deemed safe enough for the public good, what’s safe enough for you? And that’s a question no government body can answer.