Why Some People Still Haven't Got Covid

When I tested positive for Covid-19 over the winter holidays, I spent a good bit of time puzzling over how and where I was exposed. I was infected just as omicron was ripping through New York City, so it wasn’t a surprise. But I am also a fairly Covid-cautious health reporter. I wore an N95 in public settings, I’d been working from home, and I was newly boosted. How did I end up with a breakthrough infection and not, say, my husband, who goes into work every day? Why was I the one exposed, and not my unvaccinated preschooler who spends his days in the company of germy three-year-olds?

Of course, health experts have warned since Omicron took over as the dominant strain that everyone is likely to get Covid-19 at some point. And a recent survey by the US Centers for Disease Control and Prevention that used blood tests to check for coronavirus antibodies suggests that there have been many more cases than official counts suggest. Yet all of the data we have at this point suggests there are still millions of Americans who haven’t been infected.

So what gives? How can it be that two years into a pandemic marked by increasingly contagious variants, so many people remain Covid-free? What separates those of us who have tested positive from those who haven’t?

Here are a few reasons why some people have never had Covid-19 at this point in the pandemic.

Reason 1: Because vaccines, masking and distancing works

Maybe you’re sick of hearing it, maybe not. But doctors, researchers and public health experts have long been harping on the same basic preventive tools for a reason. They work.

“There are a few measures that have shown to reduce the spread of infection: getting effectively vaccinated, wearing masks indoors, and maintaining physical distance,” says Dr. Marie-Elizabeth Ramas, a New Hampshire-based family physician.

A study published just this week found, for example, that requiring masks in schools may cut infections by nearly 25%. Of course, that data comes at an interesting time, when many of the last US states with mask mandates in schools are dropping them and masks are no longer mandated in UK schools.

Ramas’ note about getting “effectively vaccinated” is an important one, reflecting that boosters have become an important tool – although less than half of people who are fully vaccinated in the US have received one at this point.

So if you’ve managed to avoid infection so far, there’s a good chance it’s because you’ve been diligent about masking up, avoiding crowds and getting your shots as soon as you were eligible.

“You’re talking to someone who has not had Covid despite it ruling my life for the past three years, and seeing tons of patients who have it. ... A lot of it is just self-management in terms of getting vaccinated and boosted [and] making sure that you have adequate PPE and being fastidious with it,” says Dr. Kevin Dieckhaus, chief of infectious diseases at UConn Health in Connecticut.

Reason 2: Because you’ve remained totally isolated

While both Dieckhaus and Ramas agreed that the vast majority of people have been exposed to coronavirus over the past two years, both note that there are some people who are seriously immunocompromised and who have largely hunkered down during the pandemic.

This is a category that includes (but is not limited to) people who have had cancer, who have had organ transplants, who are undergoing chemotherapy or who are on immunosuppressive medications. While many of these people have found ways to safely head out in public, for others, isolation has been their only real option. And let’s not forget that the millions of people with weakened immune systems need this level of protection still.

As one woman whose husband had a heart-lung transplant recently told me for a story on what it’s like to be immunocompromised in the pandemic: “What I wish people who don’t know an immune-compromised person would know is that Covid is still here and it is still a real threat to our most vulnerable members of society.”

Reason 3: Because you did actually have it, you just didn’t know

Whether or not you had Covid-19 and were simply unaware was a bigger preoccupation for people earlier on in the pandemic, when we were hopeful that a prior infection would provide longer-lasting immunity than it actually does.

Still, there is new data suggesting it’s entirely possible you fall into this category. A recent US CDC survey of more than 70,000 blood samples taken during January looked for antibodies generated after Covid-19 infection (not vaccines) and found that about 43% of Americans have been infected with the virus. That’s a much higher rate than national case counts suggest. The survey found that infections among kids were even higher. About 58% of children have had Covid-19 during the pandemic.

“This is why getting tested is so important, particularly in school-aged children,” Ramas said. “This will reduce disruption of continuity of learning and unnecessary exposure to teachers and paraprofessionals.”

Experts say the odds are very good that most of us have been exposed to the virus by now, but a few factors can make a major difference in whether you get infected or not (on top of whether you’re masked and vaccinated). One is how much virus the person is putting out, as some people shed a lot more than others. Others include how close you were to the infected person and what the ventilation was like.

Reason 4: Because household transmission is not a given

Researchers are trying to determine exactly how often household transmission happens. It’s a difficult number to pin down, in part because people’s home settings vary so widely, as do their behaviours when someone tests positive and is supposed to quarantine. (Are they masking up? Opening windows? Is everyone vaccinated, etc.?) It’s also a challenging thing to measure because the virus itself keeps changing. Omicron is more contagious than Delta. The Omicron subvariant BA.2, more contagious still.

“There are a lot of factors that we probably don’t understand,” says Dieckhaus, who adds that he and his team are studying household transmission right now.

However, the estimates we do have clearly show that household spread is not inevitable. A CDC report says that during Omicron, about 1 in 2 people in a US household developed Covid-19 if someone else was infected. Within that group, there were differences. The attack rate was lower in households where the positive person isolated, where people were vaccinated, and where people masked up.

Reason 5: Because, well, luck

While there are clear, well-established mitigation strategies that have helped lower individual risk of contracting Covid-19, “a lot of it comes down to a hefty dose of just good luck,” Dieckhaus admits.

He recalls several conversations over the past few years with patients who could not figure out where or how they were exposed, because they had been careful all along.

“There’s a lot of randomness to Covid,” Dieckhaus says. “There are people who seem to have minimal exposure who come down with it, and there are people who have heavy exposure who seem to do OK.”