Jan. 8 (UPI) -- More than 75% of people diagnosed with COVID-19 have at least one symptom of the disease six months after they were infected with the virus, a study published Friday by The Lancet found.
Fatigue and muscle weakness were the most common persistent symptoms, affecting more than 60% of study participants, the data showed.
In addition, about one in four participants reported sleep difficulties or symptoms of anxiety or depression months after they were diagnosed with the virus, the researchers said.
"Because COVID-19 is such a new disease, we are only beginning to understand some of its long-term effects on patients' health," study co-author Bin Cao said in a statement.
"Our analysis indicates that most patients continue to live with at least some of the effects of the virus after leaving hospital, and highlights a need for post-discharge care, particularly for those who experience severe infections," said Cao, a professor at the China-Japan Friendship Hospital and Capital Medical University National Center for Respiratory Medicine.
Several studies have documented long-term health complications following COVID-19 infection but new research is suggesting that these problems may affect even those who suffer less serious forms of the disease.
In one such analysis, also published Friday by the Annals of the American Thoracic Society, 62% of the participants felt they had not returned to full health and 47% had severe fatigue even 75 days after their COVID-19 diagnosis.
In addition, participants who felt they had to exert themselves during moderate exercise also reported they felt fatigued and in poor health, according to the researchers.
Less than half of the 153 patients included in this study required hospital care for their COVID-19 cases, the researchers said.
"We found that fatigue, ill-health and breathlessness were all common following COVID-19," study co-author Dr. Liam Townsend said in a press release.
"However, these symptoms appeared to be unrelated to the severity of initial infection or any single measurement at the time of an outpatient appointment," said Townsend, an infectious disease specialist at St. James's Hospital in Dublin.
The Lancet study monitored the health of 1,733 patients diagnosed with the virus in Wuhan, China, where the outbreak began, between January and May for a period of roughly six months.
During follow-up interviews and physical exams, 76% of the study participants reported at least one ongoing symptom of COVID-19, according to the researchers.
Fatigue or muscle weakness was reported by 63% of the participants, while 26% had sleep difficulties and 23% experienced symptoms of anxiety or depression, the researchers said.
Among participants who suffered more serious illness from COVID-19, 56% showed signs of severe lung function problems, according to the researchers.
Those with more severe disease performed worse in the six-minute walking test, which measures distance covered in six minutes, than those with less-serious illness, the data showed.
Thirteen percent of participants with normal kidney function when they were discharged from the hospital showed signs of reduced organ function six months later.
In 94 participants, blood tests also revealed that they had 53% lower levels of COVID-19 antibodies, or cells produced by the human immune system to fight off a virus, at six months than they did at the height of infection, according to the researchers.
This raises concerns about the possibility of COVID-19 re-infection in these patients, or their getting sick with the virus again, they said.