Nearly 7% of Americans have had long COVID, according to the CDC. Here's what we know so far about the complex condition.

Soon after the COVID-19 pandemic began, reports started cropping up about people struggling with lingering health issues from the coronavirus. Eventually the medical community formally recognized long COVID — also known as "post-COVID condition" — and researchers began to try to determine what causes people to have these long-lasting symptoms even after they've recovered from COVID-19.

Today, there are long COVID clinics across the country — and the federal government just awarded $45 million in grants to nine of them in order to expand access to care. Why is improved access important? New research shows that a shockingly high number of people have long COVID.

New 2022 data released by the Centers for Disease Control and Prevention's National Center for Health Statistics shows that nearly 7% of Americans (or 18 million people) say they've ever had long COVID, while 3.4% (or 8.8 million) say they currently have the condition.

The World Health Organization defines long COVID as the continuation or development of new symptoms three months after having COVID-19, with the symptoms lasting for at least two months with no other explanation.

The researchers found that people ages 35 to 49 were the most likely to have had long COVID (8.9%) or to currently have the condition (4.7%). The data also showed that women were more likely than men to say they've ever had long COVID, and 4.4% of women say they currently have long COVID, compared to 2.3% of men.

Eighteen million people is a lot — and doctors who treat long COVID patients say they're dealing with an influx of cases. "There is a huge unmet need in our country," Dr. Andrew Schamess, clinical co-lead of the Post-COVID Recovery Program at the Ohio State Wexner Medical Center, tells Yahoo Life. "In our clinic, people are waiting months to be seen, and there is a huge number of people who aren't being seen at all."

While many people have gotten the message that not much can be done for those with long COVID, Schamess says that's no longer the case. Here's where things stand with long COVID today, plus what to do if you suspect you have the condition.

What have we learned about long COVID so far?

There were a lot of questions about long COVID in the beginning of the pandemic, including whether it was even real. But doctors who treat long COVID patients say a lot has changed. "We have learned that it does exist," Dr. Sabiha Hussain, medical director of the Post-COVID Recovery Program at Rutgers Robert Wood Johnson Medical School and Robert Wood Johnson University Hospital, tells Yahoo Life. But, she says, "primary care physicians still need to be educated [and] there is a resistance to provide care to these complex patients, as there are no clear direction for therapeutics."

New research is focused on identifying potential biomarkers for the condition to help doctors more accurately diagnose it in patients in the future, Hussain says. One study published in the journal Nature earlier this week profiled the immune systems of 273 people with and without long COVID and found "marked differences" in myeloid cells (a tissue of the bone marrow) and lymphocytes (a type of white blood cell) in people with long COVID.

Another study, published in the Lancet late last week, analyzed MRIs of multiple organs in 531 people who had been hospitalized with COVID-19 and those without the condition. The researchers found that people who had COVID-19 were more likely to have abnormalities in their lungs, brains and kidneys than those who weren't hospitalized with the virus.

"We have had an increased understanding of the pathophysiology — the process linked with disease — of long COVID in the last year," Dr. Nisha Viswanathan, director of the long COVID program at UCLA, tells Yahoo Life. "We are increasingly realizing that 'long COVID' is more an umbrella term for various symptoms that could be caused due to a variety of reasons. This increased understanding of the causes of long COVID can ultimately inform our next steps for testing and treatments."

But there's a lot experts still don't know about long COVID. "There are so many elements of long COVID that are being investigated," Dr. Benjamin Abramoff, director of the Post-COVID Assessment and Recovery Clinic at Penn Medicine, tells Yahoo Life, including how the condition forms and how it should be treated. "While there's been a plethora of interesting research in all of these areas, I don't think we yet have definitive answers," he says.

What are the most common symptoms that linger?

The CDC has a laundry list of potential symptoms of long COVID, bucketed into general, respiratory and heart, neurological, digestive and "other" signs of the illness. Schamess says that doctors who treat long COVID patients are noticing that these patients tend to have "symptom clusters."

"The most common symptom is fatigue," he says. "There's tired and there's tired. People will describe a huge drop-off in their energy levels compared to previous levels. They have exhaustion that starts in the morning and stays with them all day." Some struggle to work and will feel "absolutely exhausted" by the end of the day, Schamess says.

People who experience this "cluster" will often have brain fog, difficulty finding words, a problem remembering common procedures at work that they used to know, absentmindedness, trouble learning new things and even issues following recipes, Schamess says.

Other symptom clusters can include having chest pains and heart palpitations; aching muscles and joints; and gastrointestinal issues, such as trouble swallowing and diarrhea, per Schamess. Some patients also experience menstrual issues, lost of taste and smell, and hair loss, he says.

But despite noticing groups of symptoms, "no two people with long COVID present the same and may have very different experiences," Abramoff says.

Are certain people more likely to get long COVID than others?

This is still being investigated, but the latest CDC data found the following people were most at risk of developing long COVID:

• Adults ages 35 to 49.

• Adults who live in medium and small metropolitan and nonmetropolitan areas.

• Women.

"Generally, the sicker you are initially, the more likely you are to have persistent symptoms," Abramoff says. He also notes that being older and unvaccinated and having preexisting conditions like type 2 diabetes, anxiety, depression, asthma, COPD and autoimmune diseases is linked with a higher risk.

The good news: Long COVID appears to be incredibly rare in children.

What are the treatment options and how effective are they?

This is still a work in progress. "There are no FDA-approved treatments for long COVID, and likely treatments that would work for one patient may not help another given the various likely biologic causes of symptoms," Viswanathan says. "At this point, we focus on management of the symptoms, making sure to really help patients with adapting to their new chronic illness."

But doctors are exploring different treatment options. "We are involved in a trial looking at Paxlovid for people with shortness of breath," Hussain says. "We are doing occupational therapy for fatigue. We have used medications like modafinil" — a drug typically used to treat excessive sleepiness, such as in narcolepsy — "with little success, as well as IVIG," or intravenous immunoglobulin, which is a treatment for patients with antibody deficiencies. She adds: "We use cognitive therapy to help with brain fog."

If you suspect that you have long COVID, doctors stress the importance of trying to be seen at a clinic that specializes in the condition. "Many of our patients have been to their doctors and have either been told there's nothing wrong with them or nothing doctors can do," Schamess says. "There are just a lot of doctors who don't know how to manage this."