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When Tangela Davidson recovered from a six-week battle with COVID, she thought the worst was behind her. But when she walked in on her husband cooking one day, and her son marveled about how great the food smelled, Davidson realized that she couldn’t smell a thing.

“It was strange, so I instantly went to my perfume bottles and started sniffing and realized I smelled nothing,” she said.

For Jackie Blakely, it was a burning sensation after recovering from COVID.

“I was walking around my house one day, then it just felt like I was walking on hot coals,” she said.

What Blakely and Davidson experienced were symptoms of Long Covid, which is defined as health problems that last four or more weeks after first getting infected with the coronavirus.

What is it?

The majority of people who have had COVID, recover within a couple of weeks. But for a growing number of people, symptoms are continuing months later. Health experts call that long COVID, and its sufferers are often called long-haulers. Long COVID is a poorly defined, poorly understood condition that occurs when COVID-19 patients’ symptoms won’t go away for weeks or months, or new ones emerge just when they think they’re all better.

For the millions of Americans still suffering from a wide spectrum of symptoms long after they’ve recovered from their original coronavirus infections, it’s unclear what the disease’s trajectory is — or even how many people are affected.

“We have millions of people in the United States whose lives are changed,” said Megan Ranney, a professor at the Brown School of Public Health, which recently launched an initiative to study the impact of long COVID. “Some of them are permanently disabled, some are partially disabled, some are able to go about their work but are different because they’re fatigued or can’t smell.”

The CDC and states do not track long COVID cases, so there are no hard numbers, but numerous studies indicate the problem runs rampant.

Early research indicates between 10 and 30 percent of people who get COVID-19 may face long-term issues. More than 42 million Americans are known to have tested positive for COVID, and the real total is most likely much higher. So even at the low-end estimate of 10 percent, that means millions of people in the U.S. and the world are “long-haulers,” facing chronic symptoms that can impair their ability to work, exercise, or lead a normal life.

There are several theories on what causes long Covid. One is that they’re caused by fragments or reserves of the virus that linger in the body. Another possible cause is persistent inflammation or damage wrought by the initial infection, affecting blood vessels, nerve pathways, or other areas of the body. The dominant theory is that long COVID is an autoimmune disease triggered by infection by an unfamiliar virus, in which victims’ revved-up immune systems continue to attack healthy tissue after the initial infection is gone. Or it could be a combination of these factors. Whatever the cause, long COVID mirrors other mysterious, chronic illnesses triggered by viral and bacterial infections.

How to tell if you have it

Typically, you don’t feel quite right, even though it’s been months since you’ve had COVID. You might be tired a lot or experiencing a lot of GI discomfort, such as abdominal pain or diarrhea. 

You might feel your heart racing– Something you didn’t notice before. Your smell and taste might still be off, and you might feel like you’re in a brain fog, with difficulty concentrating or remembering things. 

“We are seeing long COVID more often, especially in people who’ve been hospitalized,” said Ranney.

Do vaccines help prevent it?

COVID-19 vaccines are still highly effective at protecting people from getting really sick or dying, and are still quite good at keeping most people from even catching the virus or getting mildly ill.

But breakthrough infections can happen, especially with the Delta variant. And it’s becoming increasingly clear that unvaccinated people can develop long COVID symptoms, even from mild cases.

“We’ve seen that with the infection itself in the unvaccinated individuals about 30% of those individuals continue to have these long-haul COVID symptoms,” says Dr.Avindra Nath, who is studying long COVID at the National Institutes of Health.

So the concern is whether vaccinated people who get infected may be at risk for long COVID too.

“We need to behave as though there is the same chance as always of developing long COVID from a mild-to-asymptomatic infection because once you have it you can’t unring that bell and you’re looking at months to years of illness,” said  David Putrino, who studies long COVID at Mount Sinai.

Immunologists say some people may experience long COVID because the virus is still hiding in the body. In others, it may be that their immune systems overreact to the virus — a so-called autoimmune response.

Even if breakthrough infections can lead to long COVID, others say there are also plenty of other reasons vaccinated people should continue to keep being careful to avoid catching the virus.

Evidence is emerging that vaccination significantly reduces the chances of lingering symptoms, but that some vaccinated people who get breakthrough infections do in fact become long-haulers.

Hurting Black people more

If people who are socioeconomically disadvantaged to begin with suffer disproportionately from long COVID — which is likely, as they were hit hardest by the virus itself — that could just worsen societal disparities.

If left unaddressed, “we would have failed people who we already failed,” Ranney said. “It will have a generational ripple effect of people who are unable to work or unable to work to their full capacity, which certainly has economic implications, but also has mental and social implications for folks.”

Doctors who treat long COVID patients say the costs of both of their future care and lost productivity could be staggering.

“I don’t think anyone truly understands the magnitude of this,” said Denyse Lutchmansingh, who oversees the Post-COVID-19 Recovery Program at Yale–New Haven Hospital. “The majority of my patients are in the prime of their work lives, and they’re debilitated.”

Doctors have seen patients as young as 18 who “can’t form sentences.”

Return to normal

Some patients largely return to their old selves within three or four months. Many show meaningful improvement but have lingering issues. But some remain significantly impaired after a year or more, and struggle to hold jobs.

“A lot of us can’t afford our medications or groceries, and quite a few of us are going homeless,” said Amanda Finley, the founder of a Facebook discussion group for long-haulers after suffering persistent symptoms including brain fog, heart palpitations, fatigue, and shortness of breath.

Treatment generally involves managing symptoms through physical therapy, cognitive exercises, and other treatments.

Experts warn that we’ve only begun to reckon with the social and financial costs. “We’re going to need resources for many years to come to deal with these patients,” said Putrino.

Most at risk of Long COVID-19

Blacks

People over 40

Women

Individuals with underlying health conditions.

By the numbers

2/3

Vaccinated respondents concerned about long COVID

*Harris Poll

30%

Recovered COVID patients still experiencing symptoms after 6 months

*University of Washington

Most common symptoms

Nerve and muscle pain

Persistent fatigue

Breathing difficulties

Heart palpitations

Loss of smell and taste

Gastrointestinal distress

Sleep disorders

Dizziness

Numbness in limbs

Anxiety

Brain fog marked by confusion, memory loss, and inability to concentrate.