Can Breakthrough Infections Lead to Long COVID? For an Unlucky Few, Yes

When health experts talk about the remarkable efficacy of COVID-19 vaccines, they typically point to their ability to prevent severe disease and death. Fully vaccinated people can still get “breakthrough” infections from the virus that causes COVID-19—but compared to an unvaccinated person, they’re more than 10 times less likely to be hospitalized or die from their illness, according to U.S. Centers for Disease Control and Prevention (CDC) research.

Officials often point to these impressive figures as evidence that we can tame COVID-19 into a mostly mild illness that behaves like a routine cold or flu, and thus with which we can coexist. After all, the vaccines were not designed to quash viral spread entirely; they were designed to defang the virus by preventing its worst outcomes.

But people like April Zaleski know COVID-19’s worst outcomes aren’t limited to severe disease and death, even for the fully vaccinated. Zaleski, a 32-year-old from Idaho, caught COVID-19 in July 2021 after being vaccinated in January. She recovered after a couple weeks and thought the worst was behind her. But then her fatigue came back with force, along with brain fog, shortness of breath, vertigo and a skyrocketing heart rate. She began to suspect she had Long COVID, the name adopted by people who suffer symptoms long after their initial infection.

Long COVID “was on my radar,” Zaleski says, “but having been vaccinated, I hoped that my chances of that happening were slim to none.”

Indeed, the vast majority of vaccinated people who catch COVID-19 will not develop Long COVID, just as they will not die or go to the hospital; many won’t even have symptoms or realize they’re infected. But some will develop symptoms that don’t go away. Some, like Zaleski, already have. “There are so many people who are recovering from COVID, and that’s absolutely wonderful,” she says. But others “are struggling with long-term symptoms, and I just wish that people knew that side of COVID better.”

Read more: Black Women Are Fighting to Be Recognized as Long COVID Patients

In the pre-vaccine era of the pandemic, experts estimated that somewhere between 10% and 30% of people who caught COVID-19 had lingering symptoms of some kind and severity. Though it’s not entirely clear why that happens, the two leading theories are that the virus can trigger an autoimmune response that essentially makes the body attack itself, or that viral remnants sometimes linger in the body and cause lasting symptoms, says Yale University immunobiologist Akiko Iwasaki.

Vaccines have changed the game somewhat. A vaccinated person is far less likely than an unvaccinated person to get infected, according to the CDC. The agency tracked COVID-19 cases in 13 U.S. states and/or major cities from April to mid-July 2021, and found that just 8% of them occurred among fully vaccinated people. That’s good news as far as long COVID is concerned: if you don’t get infected, you can’t develop Long COVID.

But what about the unlucky people who do experience breakthrough infections? Research is just beginning to address that question.

One study, published in the New England Journal of Medicine in July, analyzed 39 fully vaccinated Israeli health care workers who had breakthrough infections. Almost 20% of them still had symptoms six weeks later. Though its sample size was small, the study demonstrated that Long COVID is possible after a breakthrough infection.

Another study, published in the Lancet Infectious Diseases in September, used self-reported symptom data from U.K. adults who tested positive for COVID-19 after being fully or partially vaccinated, as well as data from a control group of unvaccinated people who tested positive for the virus. They found that a fully vaccinated person who experienced a breakthrough infection was half as likely to have COVID-19 symptoms at least a month after diagnosis, compared to an unvaccinated person. That’s encouraging—but, again, the research showed that some vaccinated people are developing Long COVID.

Dr. Megan Ranney, who co-leads Brown University School of Public Health’s Long COVID research initiative, estimates that somewhere around 5% to 10% of fully vaccinated people who get infected may develop lingering symptoms. But, she cautions, that’s based on a very small amount of preliminary data, so it’s hard to say for sure. It’s not even clear how many vaccinated people in the U.S. have been infected—which makes it pretty hard to tell how many developed Long COVID—since the CDC stopped tracking mild breakthrough cases this spring.

Ranney says the risk of developing Long COVID is likely small enough that vaccinated people don’t need to be overly concerned. Everyone should take steps to reduce their potential exposure to the virus for many reasons, she says, but “Long COVID should not be a major driver of your decisions about what to do on a daily basis, if you are fully vaccinated.”

Nevertheless, the risk is not zero. Lauren Nichols, vice president of the Long COVID support group Body Politic—a national organization that claims some 11,000 members—says her group hears from about five fully vaccinated prospective members each week.

Anna Kern, a 33-year-old from the Detroit area, is one. She caught COVID-19 in April 2021 after being vaccinated months prior, and still has fatigue, difficulty walking or standing and a racing heart rate. “When I got COVID, there were very few people [who had gotten long COVID from a breakthrough infection],” she says. “There are more of us now, just by sheer numbers and time having passed.”

Groups like Body Politic are fighting for their recognition. “COVID isn’t just about the mortality rate,” says Nichols, 33, who developed a case of Long COVID after catching the virus in March 2020 and is still sick. “It’s [also] about the…disability and chronic illness that occurs from it.” Nichols says that aspect of the pandemic is often ignored by public health authorities, who tend to talk about COVID-19 as a binary: either you develop a severe case that can be fatal, or you get a mild case and you’re fine. Long COVID doesn’t fit neatly into either box, but that doesn’t mean it should be ignored, Nichols argues.

“Deaths and severe disease and hospitalization are…understandably what we are focused on. But Long COVID is an absolutely debilitating disease,” Iwasaki agrees. “It’s really been ignored to a large extent, and I really don’t understand why.” She says better tracking of breakthrough infections, as well as follow-up surveys that track patients’ symptoms over time (like those used in the recent Lancet study), could help increase understanding of Long COVID and the risk it poses to U.S. public health.

Without that understanding, people who develop chronic issues after a breakthrough infection, like Zaleski and Kern, may be overlooked and left out of crucial efforts to develop treatments. The National Institutes of Health has earmarked more than a billion dollars for Long COVID research—but for it to be most effective, it needs to include a diverse, representative group of people.

Read more: How COVID-19 Long Haulers Could Change the U.S. Disability Benefits System

Nichols also says health officials should look to the past, drawing on the lived experience of people who developed other post-infectious chronic illnesses, like myalgic encephalomyelitis/chronic fatigue syndrome and chronic Lyme disease, to understand how to support Long COVID patients. Better access to specialized treatment centers; funding for patient-led advocacy and research groups; and collaboration with the entire chronic-disease community would all be good places to start, she says.

And in the meantime, Nichols says public health agencies need to communicate that Long COVID is a possibility, both for unvaccinated and vaccinated people.

As for how to minimize that risk, Ranney says any policy that slows the transmission of COVID-19—such as vaccine and mask mandates or restrictions on large indoor gatherings—will be doubly effective. Not only will it prevent acute cases of the virus, but it will also naturally make Long COVID less of a risk since fewer people are getting infected.

“From a policy level,” she says, “the goal has to be reducing transmission. Period.”