Long COVID: The science shows how little we know

It wasn't long ago that people with persisting COVID-19 symptoms said they felt their doctors didn't take them seriously. Now, two or more years into the pandemic, things are changing.

We know more about the condition that's called long COVID. We know that millions of people have it worldwide. We have a better idea about what causes it, but that research is ongoing. And we won't know the long-term effects of long COVID for years.

What is long COVID?

When people get long COVID, the debilitating symptoms of an SARS-CoV-2 infection don't stop after the virus has left their bodies. Breathing difficulties, extreme fatigue and chest pain can persist for months after infection. It can make daily life — getting back to normal — challenging.

Some studies suggest that between 14-30% of COVID patients get at least one symptom of long COVID within 90 days after recovery from infection.

That means that with 395 million COVID cases worldwide (at time of writing), between 55 and 120 million people are suffering, or have suffered, with long COVID.

There is little data on the long-term effects of long COVID on individuals and society as a whole. It will take years before we have reliable data on that.

Researchers have identified a number of risk factors, but they are still trying to work out what exactly causes long COVID. It's not the same for everyone. And it is still a mystery why some people develop long COVID and why others do not.

Is long COVID less severe with omicron?

Omicron is currently the dominant variant of the coronavirus, SARS-CoV-2. And a lot of the data suggests that it causes milder infections in the majority of cases.

It's also one of the most infectious forms of COVID-19, and there are concerns that the sheer number of omicron cases could lead to a rise in cases of long COVID.

The chances of developing long COVID are higher following a severe infection, but you can get long COVID regardless of whether you have had a severe or mild infection.

What causes long COVID?

Long COVID is defined as a heterogenous syndrome — it can be caused by different factors or a mix of factors. And that means there is more than one kind of long COVID.

"There are at least two different types: One occurs in COVID-19 patients [whose infections were so severe] that they were treated in an intensive care unit with a life-threatening condition. And another can occur in individuals who had mild to moderate symptoms," said Joachim Schultze at the German brain research institute, DZNE.

The more severe form of long COVID is caused by damage to multiple organs.

To get a better diagnosis

Doctors need to understand how long COVID works — its "mechanism" — for them to properly diagnose and treat it in patients. And researchers are making progress.

Ophthalmologists in Germany, for instance, have investigated small blood vessels, known as capillaries, in the eyes of long COVID patients.

Researchers say long COVID seems to effect the shape of some blood vessels and that that can affect the blood's ability to flow through the body.

A study published in January found four major risk factors:

A high level of SARS-CoV-2 RNA in blood samples
The presence of autoantibodies, which attack the body's own tissues
Type 2 diabetes
Reactivation of a previous Epstein-Barr virus infection

Researchers have also found specific antibodies in the blood of long COVID patients.

These findings show how certain factors can increase the risk of long COVID. But they are not enough to predict whether you, or any other person, are specifically at risk.

In addition, researchers do not yet know why some patients don't get it.

Long-term impact on people and society

There's another thing we can't predict: How long COVID will affect individuals and communities over the coming years. We simply lack the data about the burden of long COVID on the global economy, communities and health services.

Those statistics are years away, as well. But researchers are tracking these developments.

Some large-scale studies aim to track people's health long after their COVID-19 infections and recovery.

Other studies aim to calculate the impact of long COVID on health systems, societies and economies.

But researchers like the DZNE's Joachim Schultze say we need more research to provide better clinical definitions and diagnostic criteria on the various forms of long COVID. They believe they will need much more data to be able to understand the full impact of the condition.

Do vaccines protect against long COVID?

Some data shows that vaccines can lower a person's risk of developing long COVID after a SARS-CoV-2 infection.

Two studies — one in Israel and the other in the United Kingdom — have found that people with two doses of a vaccine are less likely to report long COVID symptoms than unvaccinated people.

The researchers have said their findings also show that vaccines do not cause long COVID. Long COVID only occurs after a viral infection.

According to the researchers, vaccines help reduce the risks associated with long COVID in two ways.

First, vaccines help us avoid COVID-19 infections. And second, they reduce the severity of symptoms if you still do get infected.

Vaccines do not, however, fully remove the risk of long COVID. As a result, says Schultze, it's important that scientists are allowed to develop new diagnostic tools and therapeutic options for long COVID while they also continue to identify its broader impact on society.