Symptoms associated with what's often referred to as long COVID may differ depending on the variant of the SARS-CoV-2 virus a person was infected with.
Fatigue and issues involving smell, taste and hearing were more common in the first year of the pandemic, when the original "wild" form of COVID was spreading across the globe, according to a study being presented next month in Lisbon at the European Congress of Clinical Microbiology and Infectious Diseases.
But muscle pain, labored breathing, cognitive issues ("brain fog") and anxiety and depression were much more widely reported in the first quarter of 2021, when the alpha variant was dominant.
The study also found women were almost twice as likely to report long COVID symptoms as men.
Here's what we know about long COVID, including its symptoms, frequency and potential treatments.
What are the symptoms of long COVID?
Long COVID is an umbrella term for a number of new or returning health problems emerging well after the initial COVID-19 infection has ended. They range from mildly bothersome -- like fatigue, headaches and insomnia -- to more debilitating, including organ damage, blood clots, brain fog and problems with mental health.
Some lingering symptoms of COVID-19, per the Centers for Disease Control and Prevention, include:
- Difficulty breathing
- Difficulty thinking or concentrating ("brain fog")
- Chest pains
- Fast-beating or pounding heart
- Joint or muscle pain
- Pins-and-needles feeling
- Sleep problems
- Dizziness on standing (lightheadedness)
- Mood changes
- Change in sense of smell or taste
- Changes in menstrual period cycle
Dr. Nasia Safdar, medical director of infection control at the University of Wisconsin, told CNET that the key to discerning long COVID is to pay attention to new symptoms that develop or ones that never go away, starting about 30 days post-infection.
"The most common ones that we're seeing are those that are dealing with what's called higher executive functions," Safdar said. "Concentration, memory, being able to do your job the way you could before. Those kinds of symptoms are hard for people to describe, but they've clearly noticed a change from the way they were before."
Nearly two-thirds of people with long-term effects from COVID-19 experience problems with concentration and memory, according to a study from Cambridge University. Some 78% reported difficulty concentrating, 69% reported brain fog (described as sluggish or "fuzzy" thinking), 68% reported forgetfulness and 60% reported problems finding the right word in speech.
As of July last year, long COVID has been classified a disability under the federal Americans with Disability Act.
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.
According to the Mayo Clinic, the reasons for loss of smell and taste aren't entirely understood, but it's likely due to damage to the cells that support olfactory neurons.
More serious long COVID symptoms
There are also symptoms associated with long COVID that are life-threatening, including kidney damage or disease, according to a study published in the Journal of American Nephrology in September 2021.
Damage to other organs, including the brain, heart and lungs -- as well as blood clots and multisystem inflammatory syndrome -- has also been reported among people with long COVID, according to the Mayo Clinic.
A January report by the CDC said it's been found that children under 18 who had COVID-19 more than 30 days prior were more likely to be diagnosed with diabetes than those who didn't. And a large-scale study in The BMJ, a peer-reviewed journal from the British Medical Association, found that people who test positive for COVID-19 were also more likely to report new mental health issues, including anxiety and depression.
Half the patients with memory and concentration problems in the Cambridge study reported difficulties in getting their symptoms taken seriously, suggesting the medical community doesn't take cognitive issues as seriously as other symptoms.
According to the research, published in two studies in the journal Frontiers in Aging Neuroscience, more than half of the participants have been unable to work for extended periods of time and one-third said they lost their job due to their condition.
Symptoms may depend on the COVID variant
The new analysis, led by Dr. Michele Spinicci, an infectious disease specialist at the University of Florence, found symptoms of long COVID differed depending on which variant a person has been infected with.
Spinicci and his colleagues compared patients diagnosed between March and December 2020, when the original or "wild-type" virus was first encountered, to those infected between January and April 2021, when the alpha variant was dominant.
They found complaints of trouble breathing, brain fog, anxiety, depression and muscle ache increased dramatically during the alpha variant period.
Loss of smell, changes in the sense of taste and impaired hearing, which were more common among the first cluster of patients, were far less common.
Their findings also suggested patients with cases severe enough to require high-flow oxygen support were 40% more likely to experience symptoms of long COVID. Those who needed to be given immunosuppressant drugs were six times more likely.
How common is long COVID?
Exactly how many people develop long COVID -- referred to scientifically as post-acute sequelae of COVID-19, or PASC -- is still a lingering question, with different experts coming to diverse conclusions.
The CDC said it won't have data on how many Americans have long COVID for at least two years.
Some researchers have put the figure at 10% to 30% of all COVID survivors, while other studies say closer to one-half have lingering symptoms six months after their initial infection.
Safdar told CNET that the varying numbers are likely caused by differences in the population examined and who was enrolled in the study.
More than 415 million cases of COVID-19 have been reported worldwide, according to Johns Hopkins University, though many believe that's an undercount.
Of people who've been sick, a significant number have yet to feel like their old selves. More research is needed to understand why long COVID manifests, and organizations including the National Institutes for Health have launched efforts to try to understand more about the syndrome.
What causes long COVID?
Because of the huge number of people living with post-COVID-19 symptoms, we can expect research into its origins to continue for years to come. Certain demographics appear to be more susceptible: A September report from the CDC found Black people, women, people age 40 and up and those living with a preexisting medical condition were all more likely to get long COVID.
Type 2 diabetes, in particular, appears to be a major factor, according to research in the journal Cell. Other research has also pointed to lower levels of some antibodies in people who develop long COVID.
Another theory on what causes the syndrome involves microscopic blood clots: South African scientist Resia Pretorius found inflammatory molecules trapped in these microclots, which prevented cells from getting enough oxygen to perform bodily functions.
This, Pretorius wrote in an op-ed for The Guardian, "may be central to the numerous reported debilitating symptoms."
It's also possible, or even likely, that long COVID isn't caused by just one thing. The inflammation that COVID-19 causes in the body can have a myriad of effects, as can each individual damaged organ from the illness. There has also been some evidence to suggest the virus can hide in the body, as seen in the immune system's T-cell activity.
Can vaccines help prevent or treat long COVID?
COVID-19 vaccines reduce the likelihood of long COVID by lowering your chance of getting infected in the first place. But, according to a growing body of research, even in breakthrough infections the chance of symptoms that last for a month or more is lowered by roughly 50% in people who've had the primary two shots of an mRNA vaccine like the ones offered by Pfizer and Moderna.
A February report by the UK Health Security Agency corroborated that people who received both doses are less likely than unvaccinated people to report dizziness, fatigue, persistent muscle pain, hair loss, shortness of breath, loss of sense of smell and other symptoms in the short, medium and long term.
The meta-analysis, compiled from 15 global studies, also found many people who developed long COVID before vaccination "reported an improvement in symptoms after vaccination, either immediately or over several weeks."
Some individuals did, however, report a worsening in symptoms after vaccination.
Researchers have hypothesized that the reason some people with long COVID report feeling much better after getting the vaccine is due to a "reset" of their immune system. It's also possible the vaccine is helping fight off the lingering virus, though that's not the case for everyone.
What other treatment options are there?
In a Feb. 7 report in The Journal for Nurse Practitioners, researchers at the University of California, Irvine, provided anecdotal evidence that over-the-counter antihistamines may also help relieve the debilitating symptoms of long COVID for some people.
They related the cases of two middle-aged women diagnosed with the coronavirus in 2020 who developed a varied list of lingering effects months after their initial infection cleared -- including rashes, bruising, chest pain, headaches, fatigue and cognitive impairment.
Many months after these new symptoms emerged, both women took antihistamines for unrelated allergies and said their long COVID symptoms improved dramatically.
One patient stopped taking antihistamines for 72 hours and found her symptoms reappeared, only to lessen when she took the medication again. Now on a doctor-prescribed daily regimen of antihistamines, she reports regaining 90% of her pre-COVID-19 functionality.
The other reported regaining 95% of her abilities before the illness after taking the medication regularly.
Their experience bolsters a study published in The Journal of Investigative Medicine in October last year, in which 26 people with long COVID were given an antihistamine. Of them, 19 reported their symptoms either completely disappeared or were significantly decreased.
In a control group, only six of 23 patients not given the drug reported an improvement in their condition.
Dr. Lawrence Afrin, a senior consultant in hematology and oncology at the AIM Center for Personalized Medicine, told Live Science he believes mast cells, a type of immune cells that release histamine in the body, may go into overdrive in some people with COVID-19 and contribute to long COVID.
He added that there is evidence antihistamines can quiet mast cells, but more research is needed.
The information contained in this article is for educational and informational purposes only and is not intended as health or medical advice. Always consult a physician or other qualified health provider regarding any questions you may have about a medical condition or health objectives.