A four-year-old boy who was confirmed to be infected with the H7N9 bird flu on Thursday has recovered, a disease control and prevention official said Monday.

"From a clinical point of view, the boy has recovered," said Wu Fan, director of the Shanghai Disease Control and Prevention Center.

His recovery proves that not every human infection of H7N9 is severe, Wu said.

The boy will need to remain in the hospital for further observation, Wu added.

The boy's temperature is normal and he has no respiratory symptoms, said Yu Hui, director of the infectious disease department of the Children's Hospital affiliated with Fudan University, where the boy is being treated.

There are currently no standards for the discharge of H7N9-infected patients in China. For H1N1-infected patients, a full recovery period of 7 days and two negative virus tests are required before the patient can leave the hospital.

Twenty-one cases of H7N9 avian influenza have been detected thus far, appearing in Shanghai and the east China provinces of Zhejiang, Jiangsu and Anhui. Six of the cases have resulted in death.