Three cases of humans being infected by H7N9 avian influenza have been detected recently in Shanghai and East China's Anhui Province. The two in Shanghai died and the other is in critical condition, the National Health and Family Planning Commission said Sunday.

This kind of virus, H7N9, had only been detected in poultry in the past and no human had ever been infected with it, said the commission, adding that the source of the virus is still unknown.

Experts also said that there is no evidence that the virus is highly contagious from human to human, according to the commission.

Victims in Shanghai include an 87-year-old man who got sick on February 19 and passed away on March 4 and a 27-year-old man who became ill on February 27 and died on March 10.

The 35-year-old woman from Chuzhou, Anhui Province, became ill on March 9 and is in a critical condition and now being treated in Nanjing, Jiangsu Province.

All three of the victims showed early symptoms of fever and coughing, which later developed into serious pneumonia and dyspnoea, said the commission.

The Shanghai Evening Post reported earlier that the 87-year-old victim is one of three people from a family diagnosed with serious pneumonia on February 26 and hospitalized in the city's Fifth People's Hospital.

The 87-year-old's 55-year-old son also died of pneumonia in early March, and another son, aged 69, is now in stable condition. The commission added that whether the two were infected with the H7N9 virus is still under examination.

The commission said Sunday that the Shanghai Public Health Clinical Center found on March 22 that the three patients may have suffered from H7 virus and sent a sample to the Chinese Center for Disease Control and Prevention, which spotted the H7N9 virus Friday.

"Compared with the slow response to severe acute respiratory syndrome (SARS) in 2003, the speed this time is due to the public health emergency system that was established at that time," Dong Keyong, a professor with the School of Public Administration and Policy of the Renmin University of China, told the Global Times.

This helps related departments follow the development of the illness and prevent panic from spreading among the public, Dong said. 

The expert team is working to study the toxicity and human-infection capacity of the virus, and existing medicine may be helpful at an early stage of the disease but it will still take some time before a highly effective medicine comes out to cure it, the commission said.

Guo Kai contributed to this story