The Secrets of Covid ‘Brain Fog’ Are Starting to Lift

Allison Guy was having a great start to 2021. Her health was the best it had ever been. She loved her job and the people she worked with as a communications manager for a conservation nonprofit. She could get up early in the mornings to work on creative projects. Things were looking “really, really good,” she says—until she got Covid-19.

While the initial infection was not fun, what followed was worse. Four weeks later, when Guy had recovered enough to go back to work full-time, she woke up one day with...