A recent study, led by Theo Vos, professor at the Institute for Health Metrics and Evaluation (IHME) at the University of Washington, found that 6.2 percent of people who had COVID-19 in the pandemic's first two years experienced at least one of three main groups of symptoms three months later. 

Of those patients, 3.7 percent had ongoing respiratory problems, 3.2 percent had persistent fatigue with bodily pain or mood swings and 2.2 percent had cognitive problems; 15.1 percent were still affected after a year. 

The study, based on data from 1.2 million COVID-19 patients in 22 countries gathered from 54 studies and two medical record databases, was published in the journal JAMA online on Monday. 

Despite the probability of having chronic health problems from COVID-19 seems low, the large base of COVID cases worldwide – as much as 670 million – "leaves a substantial burden of disability," Bloomberg cited Dr. Christopher Murray, director of the IHME, as saying.

Dr. Tedros Adhanom Ghebreyesus, head of the World Health Organization, on Wednesday urged countries to make immediate and sustained efforts to tackle the "very serious" crisis of long COVID.

The effects of long COVID are similar to what occurs after a moderate-to-severe traumatic brain injury or complete deafness, Vos said. 

The study found that the chance of getting durable long COVID symptoms increases with the severity of the acute infection, that the average duration of long COVID was nine months for people who were hospitalized for the coronavirus, compared with four months for people who fought off the virus at home.

The study also revealed that women tend to be more affected than men – persistent symptoms occurred in 10.6 percent of women and 5.4 percent of men among patients older than 20 who caught COVID-19 three months earlier.

COVID survivors suffer higher health threat

The probability of developing long COVID is higher among people who are "middle age, rather the extremes of age," those with pre-existing medical conditions and obesity, and individuals with lower socioeconomic status and poorer access to health care, Bloomberg reported, citing Dr. Michael Peluso, an infectious diseases physician-scientist at the University of California.

Besides long symptoms, diabetes and other life-threatening conditions including heart attacks, stroke and kidney damage are more common in COVID-19 patients than those who avoided the pandemic disease, the media outlet reported.

"The pandemic will raise the baseline risk of disease and disability to a new level," said Ziyad Al-Aly, co-author of the new study in JAMA.

Beyond health issue

The U.S. Government Accountability Office estimated in March that long COVID has potentially affected up to 23 million Americans, pushing an estimated 1 million people out of work.

In June, Centers for Disease Control and Prevention (CDC) data showed that of the 40 percent of American adults who got COVID-19, nearly 1 in 5 still have long COVID symptoms. This translates to 7.5 percent of the overall U.S. adult population.

David Cutler, professor of economics at Harvard University, in September estimated that the total economic loss of long COVID could be as high as $3.7 trillion in the U.S., considering people's lost quality of life and earnings and higher spending on medical care. 

Those numbers are likely to continue to rise given the prevalence of the pandemic. More than 94 million cases and 1 million COVID deaths have been reported in the U.S., where the coronavirus infected almost 42,000 people a day on average in September.

Long COVID is not only pressuring the U.S. but also other countries, such as Australia. The Guardian reported on Wednesday that Australian doctors are struggling to meet the demand of patients seeking help for long COVID.

The Australian Financial Review earlier reported that the long COVID is costing the Australian economy $3.6 billion a year in lost output.