A study of tens of thousands of people in Scotland found that 1 in 20 people who had been sick with COVID-19 reported not recovering at all, and another 4 in 10 said they had not fully recovered from their infections many months later.

The authors of the study, published Wednesday in the journal Nature Communications, tried to home in on the long-term risks of COVID by comparing the frequency of symptoms in people with and without previous COVID diagnoses.

People with previous symptomatic COVID infections reported certain persistent symptoms, such as breathlessness, palpitations and confusion or difficulty concentrating, at a rate roughly three times as high as uninfected people in surveys from 6 to 18 months later, the study found. Those patients also experienced elevated risks of more than 20 other symptoms relating to the heart, respiratory health, muscle aches, mental health and the sensory system.

The findings strengthened calls from scientists for more expansive care options for long COVID patients in the United States and elsewhere, while also offering some good news.

The study did not identify greater risks of long-term problems in people with asymptomatic coronavirus infections. It also found, in a much more limited subset of participants who had been given at least one dose of COVID vaccine before their infections, that vaccination appeared to help reduce if not eliminate the risk of some long COVID symptoms.

People with severe initial COVID cases were at higher risk of long-term problems, the study found.

“The beauty of this study is they have a control group, and they can isolate the proportion of symptomatology that is attributable to COVID infection,” said Dr. Ziyad Al-Aly, chief of research at the VA St. Louis Health Care System and a clinical epidemiologist at Washington University in St. Louis, who was not involved in the research.

“It also tracks with the broader idea that long COVID is truly a multisystem disorder,” Al-Aly said, one that resides “not only in the brain, not only in the heart — it’s all of the above.”

Jill Pell, a professor of public health at the University of Glasgow who led the research, said the findings reinforced the importance of long COVID patients being offered support that extends beyond health care and also addresses needs related to jobs, education, poverty and disability.

“It told us that COVID can appear differently in different individuals, and it can have more than one impact on your life,” Pell said. “Any approach to supporting people has to be, firstly, personalized and also holistic. The answer doesn’t just lie within the health care sector.”

Long COVID refers to a constellation of problems that can plague patients for months or longer after an infection. Over the last year, researchers have given more attention to understanding the daunting aftereffects as the number of COVID cases exploded and health systems learned to better manage the initial stages of an infection.

U.S. government estimates have indicated that between 7.7 million and 23 million people in the United States could have long COVID.

Globally, “the condition is devastating people’s lives and livelihoods,” Tedros Adhanom Ghebreyesus, director-general of the World Health Organization, wrote in an article Wednesday for The Guardian. He called on all countries to devote “immediate and sustained action equivalent to its scale.”

The authors of the study in Scotland tracked 33,000 people who had tested positive for the virus starting in April 2020 and 63,000 who had never been diagnosed with COVID. In six-month intervals, those people were asked about any symptoms they had, including tiredness, muscle aches, chest pain and neurological problems, and about any difficulties with daily life.

By comparing the frequency of those problems with infected and uninfected people, the researchers tried to overcome a challenge that many other long COVID researchers have confronted: how to ascribe less specific symptoms to COVID when those problems are also common in the general population and may be prevalent in the midst of a pandemic.

Several of the most common long COVID symptoms identified in the study were also reported by one-fifth to one-third of participants who had never been infected, the study found. But symptoms were significantly more common in people who had previously had COVID: Those participants were more likely to report 24 of the 26 symptoms tracked by the study.

Of those with previous COVID cases, 6% said on their most recent follow-up survey that they had not recovered at all and 42% said that they had only partly recovered.

Pell said that she was still studying the trajectory of long COVID symptoms over the months and years since an infection. But the new study opened a small window onto that question. In one group of previously infected patients, about 13% of people said that their symptoms had improved over time, while about 11% said they had deteriorated.

“Some do resolve over time,” Al-Aly said, “but also there’s a good number of people who remain symptomatic with a bunch of manifestations over longer time periods.”

Only a small portion of the study participants — about 4% — had been vaccinated before their infections, and many of those with only a single dose.

“We’re now really heavily reliant upon vaccination,” Pell said, “which does confer some protection, but it’s not absolute.”

Women, older people and those living in poorer areas also faced more serious aftereffects from an infection. So, too, did those with preexisting health problems, including respiratory disease and depression.

About 9 out of 10 study participants were white, making it more difficult to determine how and why long COVID risks may have differed among racial and ethnic groups.

For health systems still working to recover from recent COVID surges while facing an onslaught of patients with the flu and other respiratory illnesses, considerably more resources were needed to treat patients suffering from an earlier coronavirus infection, scientists said.

“Our systems are not prepared,” Al-Aly said.

This article originally appeared in The New York Times.

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