We've entered year three of the pandemic, and experts still know very little about long Covid, including how to cure its symptoms.

On July 20th and July 21st, the Global Virus Network hosted the first-ever conference devoted solely to the science of long Covid. There, scientists spoke openly about what is known about the mysterious condition and the questions that remain.

For example, researchers are still searching for answers to two key questions:

• How do we define long Covid?
• Will Covid-19 medication like Paxlovid treat long Covid symptoms as well?

At this stage, even providing an estimate of how many people have long Covid is tough because symptoms vary, says Robert Gallo, co-founder and director of the Institute of Human Virology at the University of Maryland School of Medicine, who was one of the conference's panelists. 

"It'll change tomorrow and next week, and it depends on whose criteria you're using," Gallo says. "We don't even agree on how to define it yet, so it's difficult."

What is long Covid and how wide-spread are its effects?

Anecdotally, we know that many people are experiencing Covid symptoms long after infection, and data analyzed by the CDC in June shows that 7.5% of adults in the U.S. have markers of long Covid.

Currently, the agency defines long Covid as a condition that causes long-term effects as a result of an initial Covid-19 infection. These symptoms typically present long after you test negative for the virus and range from respiratory to neurological. 

Per the CDC, people with post-Covid conditions commonly report symptoms of:

• Fatigue that interferes with daily activities
• Fever
• Difficulty breathing
• Cough
• Chest pain
• Brain fog
• Headache
• Depression or anxiety
• Muscle pain
• Changes in menstrual cycles and more

The versatility of long Covid symptoms is likely due to how the Covid-19 virus affects the immune system, Gallo tells CNBC Make It. "You affect the immune system, and all things can happen," he says. "But, it also targets very widely different cells of the body."

Last year, the Americans with Disabilities Act classified long Covid as a disability due to its debilitating effects on some people.

Can clinical trials help lead us to a cure?

A huge topic discussed at the long Covid conference was the state of clinical trials. Because of the wide range of symptoms and no clear definition, choosing participants for clinical trials has been a struggle, says Eric Rubin, editor in chief of the New England Journal of Medicine and a conference panelist.

"Without a definition, it's hard to know who you should be looking at to figure out what's going on," Rubin says. Starting a clinical trial with participants who are experiencing vastly different things could negatively affect the study's findings. "Trying to decide what you're going to use as a definition is kind of the starting point to everything else," he adds. 

But, Gallo believes that we should still try to perform clinical trials with what we know now, especially because of the neurological impacts of the condition. And looking to patients could likely lead researchers to the answers they're searching for.

Recent survey data, analyzed by the CDC, was able to determine that women and people aged 50 to 59 are more likely to experience long Covid than their counterparts. Self-reported cases helped scientists discover that long Covid symptoms seem to be relatively mild, but that for some, they can be much more serious.

Still, there is no indicator of what, if anything, will provide immunity against the condition, Gallo adds. But he believes that taking medication like Paxlovid once infection is detected could be the best way to prevent long Covid symptoms. Much more research is required to determine this and further information about long Covid, but scientists are hopeful for the future.

"I'm cautiously optimistic that given the amount of attention that people are bringing to long Covid that we're going to get some answers and hopefully some interventions that help people," Rubin says.

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Don't miss:

• Long Covid is ‘continuing to increase,’ experts say. Here’s how to know if you have it — and what to do about it
• The life-altering cost of long Covid: ‘It’s a full-time job to get better’