Long COVID hinders people from normal life and work, posing significant medical and economic challenges. Nevertheless, comprehensive studies assessing its impact on large populations in Asia are still lacking. We tracked over 20,000 patients infected with COVID-19 for the first time during the Omicron BA.2 outbreak in Shanghai from March-June 2022 for one year. Of the 21,799 COVID-19 patients who participated in the 6-month telephone follow-up, 1,939 (8.89%) had self-reported long COVID symptoms. 450 long COVID patients participated in the 6-month outpatient follow-up. Participants underwent healthy physical examinations and questionnaires focused on long-COVID-related symptoms and mental health. Mobility problem (P<0.001), personal care problem (P=0.003), usual activity problem (P<0.001), pain/discomfort (P<0.001), anxiety/depression (P=0.001) and PTSD (P=0.001) were more prevalent in long COVID patients than in healthy individuals, but no significant differences were found between the two groups on chest CT and laboratory examinations. Of the 856 long COVID patients who participated in the 12-month follow-up, 587 (68.5%) had their symptoms resolved. In the multivariable logistic analysis, females (P<0.001), youth (age <40 years) (P<0.001), ≥2 comorbidities (P=0.009), and severe infection in the acute phase (P=0.006) were risk factors for developing long COVID. Middle age (40-60 years) was a risk factor for persistent long COVID one year after hospital discharge (P=0.013). The study found that long COVID mainly manifested as subjective symptoms and impacts partial patients' quality of life and mental status. After one year, most (68.5%) of the patients recovered from long COVID with no impairment of organ function observed.