The people’s guide to assessing Covid-19 risk
We are often told that humans are lousy at judging risk, and the pandemic seems to have confirmed this in spades. What else can explain vaccine hesitancy or otherwise healthy people wearing two masks as they walk alone, outside?
Yet despite all the evidence pointing to our inability to make sense of risk, I’m still optimistic we can do better. To be fair, we’ve received many confusing messages from public health officials and the media. Take this excerpt from Smithsonian Magazine:
“The Moderna vaccine’s effectiveness was at 95%, per NPR. Pfizer-BioNTech had 80% effectiveness, and Johnson and Johnson was 60% effective. On average, the three vaccines were 86% effective at preventing hospitalisation and 82% effective at preventing emergency room or urgent care visits, Vox reports.”
You’re not alone if you feel confused. Mathematical probabilities are often meaningless to people — they’re a relatively modern invention, while the human mind has evolved over thousands of years to evaluate danger. So how can you make sense of the risk you face? It’s possible to translate the data to make it meaningful, either by comparing it to other risks or by breaking it down into categories: risk to avoid at all costs, risk that should be managed closely, managed some, managed a little, or that’s not worth worrying about at all.
My risk assessment below assumes you’re already vaccinated. At this point the data is unambiguous that the majority of people have had the shot. If you haven’t yet, the risk calculation is obvious: get vaccinated! The downside of not being vaccinated is much bigger than any risks associated with the vaccine.
How likely are you to get a Covid breakthrough infection?
What does 96% versus 80% effective mean? It sounds like 20 people out of 100 who had the Pfizer vaccine will get the virus. But that 20% assumes you are exposed in a risky way. Consider this recent study from a prison in Texas that found 129 of 185 of vaccinated prisoners got a break-through infection. That’s 70% of vaccinated prisoners, much higher than the 20% we were originally told, largely because the Delta variant is more contagious, prisoners live in crowded conditions and many have underlying factors that compromise their immune response.
So that doesn’t mean seven out of 10 of us will get sick because the prison experience doesn’t generalise to the entire population. The takeaway here is that if you live in prison-like conditions — or frequent crowded dance clubs — the odds are decent you’ll get a breakthrough infection even after vaccination.
But if neither of those things describe your life and you’re in good health, you still face some risk, but it’s much smaller. If you live in an area where many people are vaccinated and there’s no large outbreak, the odds of getting a breakthrough infection are more like one in 10,000 per day. If you take that one in 10,000 risk each day (as in, living your life and going outside) the risk does add up: over the course of three months it amounts to a 1% chance, or a one in 100, chance you’ll get an infection.
Is one in 100 a reason to stay home and isolate? No, breakthrough risk falls into the “manage some” or “a little” category, depending on your risk tolerance and personal situation. But many people will want to avoid the risk entirely, or at least “manage a lot” anyway. Even though 1% sounds low, our brains do weird things when confronted with small probabilities. Going from 0% to a 1% risk has a bigger impact on behaviour than, say, 30 to 31%.
And there is a real need for some management because 1% is small but not trivial. If one in 100 people will get a breakthrough infection, you will know people, probably several, who this happens to, and seeing that will skew your perception of risk, too.
But it also doesn’t mean you should stop living your life because the odds of getting seriously ill from Covid is very small. If you’re a vaccinated healthy person, you face the same risk from Covid as you do with a mild flu. As more people get vaccinated, there will be more breakthrough cases as a share of the total population, and some may be severe enough that people die. But for vaccinated people the odds of a bad outcome are very small, and no worse than many other risks we take every day, such as dying in a bike accident, or from choking during dinner, or from an encounter with a sharp object.
If you live with a person who is immune compromised you may want to manage more, especially if they’re unvaccinated. The calculation may also change if you live with children who can’t be vaccinated. Though it’s important to remember Covid doesn’t pose much risk to children. There is some small risk of death or hospitalisation, but riding in a car or swimming poses a bigger danger to most children. It’s crucial to keep that perspective even as children make up a larger share of Covid cases, which is partly due to more infectious Delta, and also because children aren’t vaccinated while 93.5% of people over 65 are.
What about getting a booster? Boosters decrease your risk of getting a breakthrough infection, but don’t offer much additional protection for severe illness. So whether to get a booster shot comes down to how much you want to avoid getting sick altogether. For some people, especially young men at risk of myocarditis, it may not be worth it. One thing to consider is that while vaccinated people can still get infected and spread the virus, never catching it in the first place means you’ll be less infectious to others. So if you’re elderly or immunecompromised — or live with someone who is — a booster is probably good idea.
We’re all risk managers now, and with vaccines we have a great tool to reduce the danger we face. As a fully vaccinated person, your risk choices impact others to a much lesser extent than before the vaccine, so it’s a more personal calculation. Whether you want to wear a mask to the grocery store or get a booster, those choices should reflect your own risk tolerance and circumstances.
No matter what you do, there’s always a chance you could get sick, but that’s not a personal failing. The other big thing to understand about risk is that you can’t eliminate it from your life altogether.