PARIS, Feb 10, 2024 (BSS/AFP) - Tens of millions of people across the world 
are thought to suffer from long Covid, but four years after the pandemic was 
declared this elusive condition still cannot be tested for -- let alone 
treated.

However research could be finally starting to find early clues on the trail 
of long Covid, raising hopes of future breakthroughs that may also illuminate 
other stubbornly ambiguous chronic syndromes.

Long Covid is the name given to a wide variety of symptoms still being 
suffered by people weeks and months after they first contracted the SARS-CoV-
2 virus.

The most common are fatigue, shortness of breath, muscle pain and brain fog.

One notable study released last month showed there were significant 
differences in the proteins of the blood of more than 110 long Covid 
patients.

Onur Boyman, a Swiss researcher and senior author of the Science study, told 
AFP he believes this is a "central puzzle piece" in what keeps Covid raging 
for so long in the bodies of some people.

Part of the body's immune system called the complement system, which normally 
fights off infection by killing infected cells, remains active in people with 
long Covid, continuing to attack healthy targets and causing tissue damage, 
the researchers said.

Boyman said that when people recovered from long Covid, their complement 
system also improved, suggesting a strong link between the two.

"It shows that long Covid is a disease and you can actually measure it," 
Boyman said, adding the team hopes this could lead to a future test.

Researchers not involved in the study cautioned that this complement system 
"dysregulation" could not explain all the different ways that long Covid 
seems to attack patients.

Still, it is "great to see papers coming out now showing signals which might 
start to explain long Covid", said Claire Steves, professor of ageing and 
health at King's College London.

- 'Every aspect of my life' -

Lucia, a US-based long Covid sufferer who preferred not to give her last 
name, told AFP that "studies like these bring us a lot closer to 
understanding" the condition.

She pointed to another recent paper which found damage and fewer mitochondria 
in the muscles of long Covid patients, which could indicate why many patients 
become exhausted after even a small amount of exercise.

For Lucia, long Covid turned climbing up the stairs to her apartment into a 
daily battle.

When she first caught Covid in March 2020, Lucia said she could not have 
imagined how the condition would "affect every aspect of my life -- including 
socially and financially".

Lucia, a member of the Patient-Led Research Collaborative, emphasised that 
people with long Covid do not only have to deal with their many health 
issues.

They also have "to contend with disbelief or dismissal from the medical 
community or from within their social circles", she said.

The importance of supporting patients was highlighted by a BMJ study this 
week, which found that group rehab improved the quality of life of long Covid 
patients.

- Why has it been so hard? -

Ziyad Al-Aly, a clinical epidemiologist at Washington University in St Louis, 
said long Covid has been so elusive because it is a "multi-system disease".

"Our minds are trained to think about diseases based on organ systems" such 
as heart or lung disease, he told AFP.

But understanding the mechanisms behind long Covid could more broadly answer 
"why and how acute infections cause chronic disease", he said.

This means solving the mystery of long Covid may bolster the fight against 
other conditions such as chronic fatigue syndrome or lingering symptoms after 
influenza, increasingly referred to as "long flu".

While the true number of long Covid sufferers is difficult to determine, the 
World Health Organization says it could be between 10-20 percent of all 
people who have contracted the disease.

Research from the US Centers for Disease Control and Prevention has suggested 
that the percentage of people who get long Covid has decreased as new 
coronavirus variants have become less severe.

Vaccination against Covid has been shown to significantly reduce the chance 
that people will get long Covid, emphasising the importance of booster shots, 
researchers say.