Firefighter and EMS captain Hugo Sosa, who survived Covid-19, works on his recovery with a physical therapist in White Plains, New York. | Jabin Botsford/The Washington Post via Getty Images

The nagging symptoms long-haulers experience reveal a frustrating blind spot in medicine.

Dr. Craig Spencer, an emergency room doctor in New York City, was no stranger to dangerous viruses when a brush with one landed him in Bellevue Hospital for 19 days. But it was only after he was discharged, and declared virus-free, that the really bizarre symptoms set in.

Back at home, he noticed he couldn’t taste anything for several days. For months, he was tired all the time and his joints felt heavy and painful. When he woke up in the morning, his back was “stiff like a bamboo rod.” His weight dropped, and clumps of hair fell