A new American study is the latest to identify several factors that make some people more susceptible to infection with the long-term Covid virus than others. However, with millions around the world experiencing debilitating symptoms weeks or months after first becoming infected, the medical establishment does not yet understand the cause.
A new study from the University of Southern California (USC) has found that patients who were obese before they contracted Covid-19 are more likely to have long-term Covid.
The researchers also found links between specific symptoms that appeared during the initial infection and the likelihood of developing prolonged Covid-19, with sore throats, headaches and hair loss, suggesting that symptoms will persist months later.
The World Health Organization (WHO) defines Long Covid as the presence of symptoms that last at least two months and cannot be explained by another diagnosis after infection with the Coronavirus. Common symptoms include fatigue, shortness of breath and cognitive dysfunction, the World Health Organization says, noting that symptoms may fluctuate or recur over time.
Since medical professionals became aware of the prolonged Covid pandemic in 2020, scientists and researchers have been baffled by the diverse features of susceptible patients, and researchers have struggled to provide definitive answers.
Studies point to a long list of potential predictors, including recurrent Covid infections, high viral infection, presence of dormant Epstein-Barr virus, presence of autoimmune antibodies and lack of vaccination.
Some studies also conflict with each other. The University of Southern California study found no links between long Covid and age, race or gender while a June 2022 study funded by Johnson & Johnson found that the likelihood of developing long Covid syndrome was “significantly greater” among females.
“At the start of 2020, we knew nothing,” says Rebecca Livingston, lead physiotherapist in post-Covid service at University College London Hospital.
“Our thinking and understanding about LONGID has certainly evolved and the research helps us piece together some of these pieces of the puzzle. But the more we find out, the more we realize we don’t fully know yet.”
“People don’t think they have it”
Meanwhile, the prolonged Covid-19 disease is affecting millions around the world.
A British study found that an estimated two million people were living with Covid for an extended period in June 2022. The USC study found that nearly one in four people with coronavirus still reported symptoms even after 12 weeks. In Wuhan, China, a May 2022 study found that of people who were hospitalized, half still had at least one symptoms two years after infection.
The numbers are so high, in part, because the Covid-19 virus is so contagious. In the past two years, more people have contracted the Covid virus than the common cold or seasonal flu.
But those numbers are also likely to be underestimated. “People don’t think they have it,” says Ruth Ainley, a respiratory physiotherapist and long-term Covid specialist. “They think they’re tired all the time because they had the virus, so they don’t put two and two together.”
Even when people think they are unwell, some people are more likely than others to seek medical help. “The data we have will tell us that the majority of people with long-term Covid disease are women, that they are middle-aged and they are white,” Livingston says.
“This data also reflects the people we see in the clinic, and we know there are huge disparities in terms of access to … health care, so it probably doesn’t fully represent the whole picture.”
News articles have often focused on the trauma caused by the prolonged illness of Covid, which causes young people, both healthy and athletic people, to develop debilitating symptoms. But those with very active lifestyles may be more likely to notice symptoms such as fatigue, and take these symptoms more seriously than older adults.
“Older adults are severely underdiagnosed,” Ainley says. “They were written off because they haven’t gotten rid of Covid, or they’re a little tired and that’s to be expected at their age.”
Even among patients known to have had Covid for a long time, the complex nature of the disease makes analysis difficult. There are more than 200 recognized symptoms of Covid, according to the American Medical Association, which estimates that about 20 to 30% of patients are affected, even after a mild initial illness.
There are a few recognizable patterns of when symptoms appear or how long they may last.
“We expected, when we started working with people after Covid, that we would evaluate them systematically and fit into the categories. But the truth is it’s a lot more murky,” Livingston says. “People will have symptoms that affect many different systems, and some people have some.” Symptoms only. It makes it very difficult to piece together the picture.”
The prolonged impact of Covid on the lives of many patients is significant. In addition to physical symptoms, a 2022 National Institutes of Health study found that a “significant” number of patients — more than a third — had PTSD, anxiety or depression three months after symptoms began.
“You see really heartbreaking cases every day,” Livingston says. “It’s a really difficult situation to live with.”
Waiting for the “aha moment”
Looking to the future, there is some hope.
Ainley compares the struggle to understand Covid-19, and the prolonged Covid virus in particular, to early experiences with HIV, when little was known about how the virus was treated or how it spread. Now, HIV isn’t a death sentence like it used to be, but that took 30 to 40 years. The problem with Long Covid is that we’re two years into this and we don’t understand enough of the mechanisms on how it works.”
Livingston expects that as more representative data emerges about who has had Covid for a long time, more patterns will emerge to shed new light on who is at risk.
“Every bit of the research is cutting edge and helping advance our understanding,” Livingston says. “I would like to think there will be an aha moment sometime in the future. You have to hope for that when you are a doctor or a patient.”
As cases continue to rise in Europe and the United States, taking steps to prevent Covid infection in the first place remains the best line of defense.
And for those who are already sick, research may soon provide much-needed answers. “There is research to look at why people are affected by things, but there is also research that needs to look at how we treat people and how we help them recover,” Livingston says.
“Long Covid is something we have to think about and treat for a long time. But we know that people are recovering and that there are ways to rehabilitate that can help people.”
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