Nearly one-third of people with COVID-19 experience lingering symptoms up to nine months after their diagnosis, even if they initially had a mild case, a small new study suggests.

The study researchers, from the University of Washington, analyzed information from 177 people in the Seattle area with confirmed COVID-19 infections who were followed for three to nine months after their diagnosis. (The average follow-up time was six months.) Most participants — 150 people, or 85% of the study group — had a mild case of COVID-19 and were not hospitalized; 11 participants (6%) were asymptomatic; and 16 participants (9%) were hospitalized.