Two-and-a-half years after long COVID-19 sufferers coined the term, experts are still trying to wrap their brains around this variable and complex syndrome.

What needs to be done to move the needle?

The growing body of work on long COVID-19 is hampered by a lack of consistent definitions, data and study designs.

“Different health agencies have provided various clinical definitions for this condition, making it even more challenging to reach uniform conclusions across comparable studies,” said Bhramar Mukherjee of the University of Michigan School of Public Health.

Progress is further muddied by the sheer quantity of symptoms and affected systems.

Possible mechanisms range from inflammation to autoimmune effects and viral reservoirs, and data on causal links and risk factors remain inconclusive.

“There should be a little bit of caution when we read these studies, because a lot of these studies were done on patients who were hospitalized for their initial infection,” said pulmonologist Dr. Alexander Truong of Emory University, who recently co-founded a post-COVID-19 clinic.

“In our clinic population, most of our patients have never had to be hospitalized or never sought medical care for their initial infection, and thus the data that we're reading in the literature may not be reflective of what we're seeing in our clinics,” he said.

But Truong sees cause for hope.

“We are getting better and better at taking care of these patients, although we are still very, very much in the very, very beginning stages of doing so,” he said.

Mukherjee agrees. She said scientists are making headway.

“And the science is still evolving. That's not necessarily a bad thing. Because as we know more, and we share more, and we change our positions – that’s how you progress with a new disease,” she said. “That does not mean that you should lose trust.”

Mukherjee said the pandemic underlined the value of nationally integrating data on vaccines, infections and clinical outcomes, and the need for more countries to do so.

For now, the best advice is not to get COVID-19.

“Prevention is really the only form of treatment,” said Dr. Christian Sandrock of the UC Davis Medical Center, who also leads a post-COVID-19 clinic. “You avoid this disease, you're not going to get long COVID.”

He added that long COVID-19 is a syndrome that differs widely from person to person, and treatment and management approaches need to reflect that fact.

In short, experts say doctors should believe their long COVID-19 patients and treat their symptoms.