That matters for two reasons. First, it’s still possible that someone who’s been vaccinated could actually get sick—the risk is very slender, but not zero. And second, because unvaccinated people can be infected with Covid-19 and transmit it to others without showing any symptoms, it remains possible that someone vaccinated could also still be, in effect, a carrier.
Now, it seems pretty clear that all the vaccines will stop some infection and transmission, maybe quite a lot. “The data are all pretty consistent with that number being a two-thirds reduction,” says Bob Wachter, chair of the Department of Medicine at UC San Francisco. “Maybe it’s a three-quarter reduction or a 60 percent reduction, but the key thing is it’s a substantial reduction in the probability you will catch it, carry it, feel fine, and spread it to someone else.”
Given all that, my vaccinated aunt and uncle visiting my folks seems like the easiest scenario. Everyone involved is protected against serious illness, and everyone’s at least somewhat protected against getting infected and transmitting it. “I’m confident enough that between my protection as a vaccinated person and the decreased probability that another vaccinated person is going to have it and spread it, when you do the math there the chances that something bad is going to come between vaccinated people are really, really small,” Wachter says.
The risk here is even smaller given that my aunt and uncle have been just as cautious as my mom and stepdad—maybe even if they see someone else on their trip. Risk, in this sense, is additive. “I think it makes sense that two vaccinated households that aren’t mixing with other, non-vaccinated households could get together indoors for dinner,” says A. Marm Kilpatrick, an infectious disease researcher at UC Santa Cruz. “That initially sounds risky, but since both households are vaccinated, the risk of anyone getting sick even if someone was infected is much lower. And if neither household is mixing with other people, their risk of being infected to begin with is very low.”
Broadly, vaccinated people don’t have nothing to worry about, but they have far less than the rest of us. They can probably fly on an airplane, if they keep their masks on. Eating indoors at a restaurant? Eh. Maybe not yet. More exposures, more risks for everyone.
Meanwhile, the kind of gathering my mom is pitching here is like having lots of defenses layered together—multiple people with multiple protections against illness and transmission, like the “Swiss cheese model” of risk-reducing non-pharmaceutical interventions, only this time all stacked up and administered in a hypodermic needle. Green light! Dinner like it’s 2019.
Scenario Two: The Stepsister and Mother
“Neither has gotten vaccinated, and they socialize with others.” —Mom
This one has the biggest yikes factor. I told Mom that while she and Stepdad had a massively reduced risk of getting sick themselves, it wasn’t zero. They’re back in mask territory here. “I personally still feel like wearing masks is very reasonable,” says Grace Lee, an infectious disease physician at Stanford Children’s Health and member of the CDC’s Advisory Committee on Immunization Practices. “My hope is, they will be safer if they continue to mask and use good hand hygiene and control what they can, but their risks are mitigated a lot by getting vaccinated.”
Mom and Stepdad don’t want to get sick, and—improbable though it may be—they don’t want to get Stepsis and her mom sick either, or end up as links in some longer epidemiological chain. My rule in this pandemic has been: Don’t become the main character in a CDC case study. It’s unlikely, but still possible, that vaccinated people could be an infectious bridge between unvaccinated households. Kilpatrick’s rough calculations of how much the vaccines reduce infection and transmission are an optimistic 80-to-90 percent, but that’s still not perfect. “It’s much safer than when they weren’t vaccinated, but not high enough to be low risk,” he says.