Long COVID-19 support groups in the UK are calling for more funding and research to help better understand the condition.
With wide-ranging symptoms affecting a large number of people, many clinicians admit there is a lot they still don't know.
And for some, the fight has been persuading people there is actually something wrong with them
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One of those people is Jo House, from Bristol, England. She's more than a year into her battle with Long COVID-19.
Her daily struggles are believed to also be a problem for millions across the world.
"My fatigue and my brain fog are pretty bad at the moment. Which makes it really hard for doing anything cognitive. I can't think when I last read a book. I read a couple of pages and I get too tired. This week there's been at least three days when I've spent most of the day in bed," she told CGTN Europe.
Her home region in southwest England is being held up by many as a success story, and a beacon for others to copy when it comes to tackling the condition.
Many of those struggling are being referred to clinics which aim to manage the symptoms. One of those is being run by Sirona Care And Health.
A survey by LongCovid.org found that almost 70 percent of people suffering from Long COVID-19 in the UK said they were too unwell to work full time. /CFP/
Clare Cook is a physiotherapist on the front line of the service. She is trying to tackle an illness about which more is unknown than known.
She says that one of the difficulties is that there is not a correlation between having been seriously ill with COVID-19 and suffering from Long COVID-19.
"So actually, if I was 10 out of 10 poorly, I'm not going to have 10 out of 10 Long COVID-19," she said.
"The population of people most burdened by acute disease compared with Long COVID-19 are actually quite different populations," she added.
"So it is important to think that the experience you have now is valid, it matters if you're burdened."
There are now official public health guidelines in the UK to identify and help those suffering. But part of the battle for House and others has been persuading people that the condition actually exists.
"It feels really stressful and anxiety-inducing. And on the other hand when you are believed and are listened to it's such a relief," she said.
"I know this is a new disease and not a lot is known about it yet… But I just can't emphasize enough that people just want to be heard and believed by the medical profession, by their workplace, by their families."
A recent survey carried out by LongCovid.org found that just over 80 percent of those who thought they had the illness in the UK had not been referred to a specialist.
And there's a growing need to try and address the problem. It is thought that more than one million people in the UK alone have the disease.