In another blow to those who claim COVID-19 is just like the flu, researchers have found more than three-quarters of hospitalised patients still suffer symptoms six months after falling sick.
The most common is fatigue or muscle weakness, researchers from Wuhan Research Center for Communicable Disease Diagnosis and Treatment said on Saturday (NZ time), in 63 percent of patients, followed by difficulty sleeping and anxiety/depression.
"Because COVID-19 is such a new disease, we are only beginning to understand some of its long-term effects on patients' health," said Bin Cao, who led the new study.
Scientists looked at the experience of 1733 hospitalised patients who caught the SARS-CoV-2 virus in Wuhan, where it was first detected, between January and May.
Patients that had more serious illness in the acute phase were more likely to suffer long-term effects, the study found. It's a condition that's been dubbed 'Long COVID'.
Thirteen percent were suffering from ongoing kidney problems. Many had reduced lung function, particularly if they'd required previously required ventilator support.
Levels of neutralising antibodies fell an average of 52 percent in the six months after falling ill, the study found, raising "concerns about the possibility of COVID-19 re-infection".
A similar Irish study published this week found nearly half of all patients - hospitalised or not - report serious fatigue a few months down the track.
Only 4 percent of the 1733 patients in the Wuhan study needed ICU treatment, suggesting COVID-19 can have long-term effects even after moderate infections.
"Patient outcomes after ICU stays suggests that several COVID-19 patients who were critically ill while hospitalised will subsequently face impairments regarding their cognitive and mental health and/or physical function far beyond their hospital discharge," an editorial published alongside the study in medical journal The Lancet said.
The findings from China come a day after modelling by US researchers found more than half of all COVID-19 infections are spread by people who aren't showing symptoms themselves.
Just over a third of transmission is by presymptomatic people, and just under a quarter by people who never develop symptoms at all.
"The proportion of individuals with infection who never have apparent symptoms is difficult to quantify because it requires intensive prospective clinical sampling and symptom screening from a representative sample of individuals with and without infection," the study, published in JAMA Network Open on Friday, reads.
"Nonetheless, evidence from household contact studies indicates that asymptomatic or very mild symptomatic infections occur, and laboratory and epidemiological evidence suggests that individuals who never develop symptoms may be as likely as individuals with symptoms to transmit SARS-CoV-2 to others."
This is why health authorities and scientists have urged people to wear masks when in public or indoors with people outside their home 'bubble' whether they're feeling sick or not.