Three cases of human infection with H7N9 avian influenza have been detected recently in Shanghai and Anhui Province, and two of them have died, the other being in a critical condition, the National Health and Family Planning Commission said Sunday.

The victims include an 87-year-old male in Shanghai who got sick on Feb. 19 and died on March 4, a 27-year-old male in Shanghai who became ill on Feb. 27 and died on March 10, and a 35-year-old female in Chuzhou City of Anhui who became ill on March 9 and is now in a critical condition.

They all showed initial symptoms of fever and coughs which developed into severe pneumonia and difficult breathing in later stages, according to the report.

On Saturday, the three cases were confirmed to be human infection with H7N9 avian influenza by an expert team summoned by the health and family planning commission, based on clinical observation, laboratory tests and epidemiological surveys.

On Friday, the Chinese Center for Disease Control and Preservation separated the H7N9 bird flu virus from body samples of the patients.

So far, the commission said, it is unclear how the three got infected, and no mutual infections were discovered among them. Besides, no abnormalities were detected among 88 of their close contacts.

The subtype of H7N9 bird flu virus has not been contracted to human beings before. The virus shows no signs of being highly contagious among humans, according to the clinical observation on the cases´ close contacts.

However, as only three cases of human infection of H7N9 have been found, relatively little research has been done on it. The expert team is working to study the toxicity and human-infection capacity of the virus, according to the commission.

There are no vaccines against the H7N9 bird flu virus either at home or abroad.