For many people, what started out as a relatively mild case of COVID-19 persisted into a lingering condition that took weeks or months before their suffering subsided -- some have yet to fully recover. They live with long COVID, a condition health care providers have struggled to understand and accurately diagnose since the COVID-19 pandemic was declared in March 2020.
Though it's hard to put a number on what percentage of people will develop long COVID, since home tests and mild cases contribute to inaccurate case counts, somewhere between 10% of people who tested positive for COVID-19 but didn't need to be hospitalized, and 50% to 70% of people who were hospitalized, developed some degree of long COVID, according to a major review of long COVID research published earlier this year in Nature Reviews Microbiology.
Fortunately, rates of long COVID, also called "long-haul COVID" or "post-COVID conditions," may be declining. A Kaiser Family Foundation analysis of data from the US Centers for Disease Control and Prevention found that the number of people who reported COVID-19 symptoms that lasted longer than three months, currently or in the past, declined from 35% in June 2022 to 28% in January 2023.
The condition can be mildly bothersome or debilitating, running the gamut of loss of smell, nausea and constipation, to organ damage or life-changing mental or cognitive symptoms. Non-specific symptoms that can easily fall into the category of other health conditions, like breathlessness, chronic headaches and chest pain, can make accurately diagnosing long COVID feel like catching a shadow.
Despite what researchers are still trying to figure out, including more treatment options, better diagnostic tools and other factors, health care providers and scientists have made headway in their understanding of the condition. Here's a roundup of what we know today.
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What are the symptoms of long COVID?
After an initial infection is cleared, COVID-19 can linger and affect just about every system of the body, depending on the person. Symptoms include heart or cardiovascular problems, respiratory issues, immune system effects, neurological symptoms and even some reproductive issues.
Dr. Nasia Safdar, medical director of infection control at the University of Wisconsin, told CNET in 2021, when scientists were first getting a grip on long COVID, that the key to discerning the condition is to pay attention to new symptoms that develop or ones that never go away, starting about 30 days post-infection. This separates long COVID from the initial viral infection itself.
While it's not a full list, some lingering symptoms of COVID-19, per the US Centers for Disease Control and Prevention and a review of long COVID research by Nature, include:
- Difficulty thinking or concentrating ("brain fog")
- Difficulty breathing, shortness of breath or cough
- Chest pains
- Headache or migraines
- Fast-beating or pounding heart
- Joint or muscle pain
- "Pins-and-needles" feeling
- Nausea, diarrhea or other gastrointestinal problems
- Sleep problems
- Dizziness upon standing (lightheadedness)
- Mood changes, such as depression or anxiety
- Change in sense of smell or taste
- Reproductive system problems, including changes to the menstrual cycle and erectile dysfunction
In 2021, Safdar said the most common symptoms she saw in her work with patients were symptoms that affected "higher executive functions."
"Concentration, memory, being able to do your job the way you could before," Safdar said. "Those kinds of symptoms are hard for people to describe, but they've clearly noticed a change from the way they were before."
In 2023, cognitive impairment and neurological symptoms are still relatively common for those who experience effects post-COVID-19. The authors of the Nature review called them a "major feature of long COVID," with a meta-analysis finding fatigue in 32% of people with COVID-19 after 12 weeks, and cognitive impairment in 22%.
One set of symptoms of COVID-19 that affected many people sick from earlier variants is the loss of their sense of taste, smell or both. For some, ageusia (loss of taste) and anosmia (loss of smell) don't just affect how they enjoy their food or a favorite scent, but can meddle with their memories and mental health.
The 'typical' long COVID patient
People ages 36 to 50 were most likely to be diagnosed with long COVID, according to a Fair Health study. The study, which looked at data from more than 78,000 patients from October 2021 through January 2022, also found more diagnoses in women than in men, and that about 30% of people had no prior diagnosis with a chronic health condition.
Other factors that may make a person more likely to develop long COVID is being unvaccinated and having underlying health conditions pre-COVID-19, including type 2 diabetes and a past bout with Epstein-Barr virus (the virus that causes mono), according to the Nature review.
People who need to be hospitalized after contracting COVID-19 are also more likely to develop long COVID. Socio-economic factors also may make someone more susceptible, as having a lower income and being unable to take off work to rest increases the risk of long COVID, according to the Nature review.
In short, there is no "typical" patient with long COVID, since people with more mild cases can and do develop the condition, as do children. In children, those who have attention deficit hyperactivity disorder, chronic urticaria and allergic rhinitis (allergic reactions including hives and seasonal allergies) may be more likely to develop long COVID, research shows.
The various conditions or factors that seem to increase someone's chances of developing long COVID highlight the complexity of the disorder, the different ways it interacts with the immune system and brain and its varying causes.
Causes of long COVID
The authors of the Nature review say that there are "likely multiple, potentially overlapping, causes of long COVID." Some of these mechanisms, they conclude, include viral persistence (the virus staying with the body's tissue), neuroinflammation, excessive blood clotting and autoimmunity or disruptions to immune response.
Dr. Devang Sanghavi, a critical care physician with the Mayo Clinic, told CNET in August 2022 that there are a few broad ways to consider the different causes of long COVID: People with severe enough afflictions that they developed organ or cell damage; people who were hospitalized and have lingering health effects from that hospitalization; and people who weren't hospitalized, but developed symptoms as a response to the virus. The last group, in particular, has been the focus of research into how some people's immune systems respond, or even over-respond, to the virus.
The different causes and mechanisms of lingering symptoms and health effects illustrate the complexity of COVID-19 and its ability as a respiratory virus to create lasting impacts on other parts of the body.
No long COVID 'test'
According to the CDC, there is no single test that can determine whether or not you have long COVID. Instead, a health care provider looks at your health history, including if, when and the likelihood you had COVID-19 (based on a positive test result, your symptoms or exposure history), and when symptoms of long COVID began.
This lack of any sort of definitive marker makes a long COVID diagnosis even more frustrating for people suffering. And while health care providers are more aware of its presence this year than earlier in the pandemic, blood work or other routine tests may turn up normal in patients with COVID-19, requiring them to do their own advocacy to get the treatment they need.
"One message that I would like to send out to these patients is that their symptoms are real," Sanghavi said of the difficulties of living with, diagnosing and treating long COVID.
"We may not have answers right now about why and how and what we can do to help them, but they should not be struggling and suffering alone," Sanghavi said.
Because long COVID symptoms are so broad, there is no blanket treatment. Instead, treatment for long-haul COVID, according to Johns Hopkins Medicine, will likely involve doctors working to address your symptoms. Therapy will depend on your symptoms, and various breathing exercises, physical therapy or medications may be prescribed, per Johns Hopkins.
Because the symptoms of long COVID can overlap so evenly with symptoms of chronic fatigue syndrome (ME/CFS), another disabling and lasting health condition, strategies used for ME/CFS patients may also work for long COVID patients, according to Nature.
Trials on the effects of different drugs for treating long COVID, including anti-inflammatory and anticlotting medications and antihistamines, have also been started. Depending on your symptoms and health history, your doctor may recommend a specific medication. There's also some early information to suggest that COVID-19 antiviral medications, such as Paxlovid, might reduce the risk of long COVID, as Nature reported in a March article, but more research is needed.
Survivor Corps, an organization for people with long COVID, has a map of post-COVID care centers for patients who are looking for more resources or treatments.
Preventing long COVID: The role of reinfection and vaccines
Researchers know that having a severe case of COVID-19 can make it more likely for a person to experience long COVID, and that vaccines reduce that risk of severe disease. While research is ongoing, Johns Hopkins Medicine says "it is likely that being vaccinated reduces the risk" of long COVID.
But research on how vaccines impact the symptoms of people who already have long COVID is unclear. One smaller study found that a little more than 16% of people experienced a relief of long COVID symptoms post-vaccine, but about 21% actually experienced a worsening of their symptoms. Most didn't experience a change. A review published online by The Lancet also found mixed results on vaccines for long COVID symptoms.
Because COVID-19 is still around, reports of people getting reinfected with COVID-19 a second, third or even fourth time are becoming more common. And early research, according to the authors of the Nature review, shows that there is an increasing risk of long COVID after second and third infections with COVID-19.