When these patients were retested after six months, their levels of neutralising antibodies were 52.5 per cent lower.
As the pandemic unfolded across the globe, patients joined Facebook groups, Twitter feeds, and other online support groups to share their stories of the symptoms that they were experiencing post-COVID, bringing visibility to an issue that has come to be called 'Long COVID'.
Professor Cao added, their research underscored the need for ongoing care for patients following discharge from hospital, specifically those who have suffered from severe infections.
"To our knowledge, this study is the largest cohort study with the longest follow-up duration for the consequences of adult patients discharged from hospital recovering from Covid-19", wrote researcher Chaolin Huang, of Jin Yin-tan Hospital, Wuhan, China, and colleagues in The Lancet, published online January 8.
Patients, who had an average age of 57, were visited between June and September and answered questions on their symptoms and health-related quality of life.
"Because COVID-19 is such a new disease, we are only beginning to understand some of its long-term effects on patients' health", said researcher Dr. Bin Cao, from the National Center for Respiratory Medicine at the China-Japan Friendship Hospital and Capital Medical University, both in Beijing.
The study found more than 50 percent of patients had residual abnormalities in their chest imaging, and about 13 percent of patients whose kidney function was normal while in the hospital had reduced kidney function in follow-up exams.
In a Lancet commentary on the Chinese study, foreign scientists said it is rather surprising to find that some COVID-19 patients with good kidney health experienced lower than standard kidney function measured by the rate at which their kidneys are cleaning their blood, a key indicator of renal health.
The team explained, longer-term multidisciplinary study now being conducted would help in improving the understanding and development of treatments to alleviate the long-term effects of COVID-19 "on multiple tissues and organs". The discharged patients also went through some physical examinations, lab tests and a six-minute walking test to scale their tolerance levels.
Fatigue or muscle weakness was reported by 63%, while 26% had sleep problems.
The study revealed that patients with more severe illness commonly had reduced lung function, with 56 per cent (48/86) of those at severity scale 5-6 (who required ventilation) experiencing diffusion impairment - reduced flow of oxygen from the lungs to the bloodstream. And he's seen similar issues among patients at his hospital.
The authors said this raises concerns about the possibility of Covid-19 re-infection, although they said larger samples would be needed to clarify how immunity to the virus changes over time.
The study was conducted at the Jin Yin-tan Hospital which was the first designated medical facility in Wuhan, China for Covid-19 patients, according to the researchers.