Long covid still confounds us. Here’s what is now known.

“We know a lot about this particular coronavirus,” said Francesca Beaudoin, chair of the department of epidemiology at Brown University. “That does not translate into an understanding of the long-term consequences of infection.”

As many as 7 percent of Americans report having suffered from a slew of lingering symptoms after enduring covid-19, including fatigue, difficulty breathing, brain fog, joint pain and ongoing loss of taste and smell, according to the Centers for Disease Control and Prevention. But there is still no clearly defined cause of, or cure for the syndrome.

The costs of our lack of understanding are vast, Beaudoin and others say, creating a huge new burden on the health-care system, as people report limitations in their daily activities including being able to work.

...