More than 200 lingering symptoms have been reported in patients who suffer ongoing health problems after a COVID infection.

Now a new study has identified 12 key symptoms that best define the debilitating condition known as long COVID.

The findings, published Thursday in JAMA, are based on 9,764 participants in a study called the RECOVER initiative, which stands for researching COVID to enhance recovery, a four-year, $1.15 billion study of long COVID funded by the National Institutes of Health.

The research is expected to help standardize the definition of long COVID and have a significant impact on how the condition is diagnosed and studied, said Leora Horwitz, a physician and co-principal investigator for the RECOVER Clinical Science Core at NYU Langone Health.

“If you look up simple questions like ‘how many people get long COVID,’ the answers are all over the place because people define it differently,” Horwitz said. “To really advance the science, we need a common language.”

In addition to identifying the key symptoms of long COVID, the study used a point scoring system based on how likely the symptom was a true signal of long COVID versus another condition.

For instance, when researchers analyzed patients’ self-reported symptoms, they found that some symptoms were more common in people who had been infected with COVID, but were less common in people who never had COVID.

These included loss of taste or smell or post-exertional malaise, which is a worsening of symptoms following even minor physical or mental exertion. Other symptoms, such as brain fog or chest palpitations, were found to be common in long-COVID patients, but were also common in other conditions, so those symptoms received fewer points.

The 12 symptoms of long COVID

To meet the study’s definition of long COVID, a participant needed to score a total of 12 points once all their symptoms were added up. The 12 key symptoms and their corresponding scores are:

• Loss of smell or taste: 8 points.

• Post-exertional malaise: 7 points.

• Chronic cough: 4 points.

• Brain fog: 3 points.

• Thirst: 3 points.

• Heart palpitations: 2 points.

• Chest pain: 2 points.

• Fatigue: 1 point.

• Dizziness: 1 point.

• Gastrointestinal symptoms: 1 point.

• Issues with sexual desire or capacity: 1 point.

• Abnormal movements (including tremors, slowed movements, rigidity, or sudden, unintended and uncontrollable jerky movements): 1 point.

In general, the higher someone’s score was, the worse their ability to carry out every day activities, said Tanayott Thaweethai, study lead author and researcher at Massachusetts General Hospital and Harvard Medical School. Higher symptom scores also correlated with a lower quality of life, he said.

“This offers a unifying framework for thinking about long COVID, and it gives us a quantitative score we can use to understand whether people get better or worse over time,” he said.

Researchers cautioned that the findings are preliminary, and that it is too soon to use the symptom list and scoring system to diagnose long COVID or determine eligibility for disability benefits.

Horwitz said she expects the definition of long COVID will continue to evolve and get refined by researchers, but called this study a “huge first step” toward creating a standard definition. The next step is for researchers to validate the study results and compare them against lab tests and imaging.

Currently, the World Health Organization defines long COVID as having any new symptoms three months after an initial COVID infection, where the symptoms have lasted for at least two months with no other explanation. While the definition is inclusive and flexible, it doesn’t clearly define long COVID for researchers, Horwitz said.

Based on the 12 defining symptoms, the rate of long COVID among different groups in the study ranged from 10 to 23 percent, depending on when they were infected and whether they had entered the study already having a diagnosis of long COVID.

The high end of the range may be largely due to an over representation of people who had long COVID before they enrolled in the study, said Andrea Foulkes, senior study author and principal investigator of the RECOVER Data Resource Core at Massachusetts General Hospital and Harvard Medical School.

Researchers say that they suspect the real world incidence of long COVID is closer to about 10 percent of people who contract the illness, based on the rates seen in people who joined the trial within 30 days of contracting COVID and who didn’t yet know if they might develop long COVID.

This study also found that long COVID was more common in people who were unvaccinated and in people who had been infected with COVID more than once.

Some of the most distinguishing symptoms for long COVID were not necessarily the most common, or the most debilitating, researchers said.

“There are many other symptoms that participants are experiencing above and beyond those 12 symptoms,” Foulkes said.

For example, symptoms such as headaches and muscle aches are very common among long-COVID patients, but are also not uncommon in people who have never had COVID. Thirst and abnormal movements, such as tremors or seizures, are not common, even among people with long COVID, she said, but the symptoms were significantly more present in people who have had COVID versus people who never had the illness.

While some patients expressed concern that the 12-symptom list could exclude some long-COVID patients, Nitza Rochez, 45, who lives in the Bronx, said she is grateful to finally have a definition.

“Personally I think that the list of symptoms is too small, but I understand that you have to start somewhere,” she said. “At least it’s more than what we’ve had in the last two years.”

Rochez is a RECOVER study participant and has been coping with long COVID since she was first infected in March 2020. In that time, she has experienced all of the 12 symptoms that researchers identified, but also has other symptoms that aren’t on their list, like stuttering.

“Honestly it’s a horrible experience, and I wouldn’t want someone to go through it as blindly as I have been,” she said. “Having a definition would have alleviated my anxiety so much because it would have a name as opposed to not knowing what’s going on with my own body.”

Marta Cerda, 61, of Chicago, said she is hopeful that having a clear definition for long COVID can help reduce skepticism around the condition and make it easier for people to get diagnosed or get disability benefits.

Cerda, a RECOVER study participant, was first infected with COVID in November 2020, but when she experienced strange symptoms after her infection, like stomach pain, she didn’t initially realize that it could be connected to her COVID infection.

“The closer we get to defining it, the closer we can get to educating physicians so that they can help us,” she said.

In the study, researchers also attempted to cluster patients based on their symptom patterns to see whether long COVID had distinct subgroups. Horwitz said that patients tended to have symptoms across multiple areas of their body, indicating that long COVID was “likely a total body disease.”

Thaweethai said the study further reinforces the idea that there are overlaps between long COVID and other conditions that existed before the pandemic, such as an autonomic nervous system disorder called POTS, or postural orthostatic tachycardia syndrome and another condition called myalgic encephalomyelitis (ME/CFS), also known as chronic fatigue syndrome.

In future studies, researchers plan to look at questions around whether long COVID should be identified and defined differently in children and adolescents.