Hong Kong (CNN) -- Two people in China have died and another remains critical after falling ill with a strain of bird flu not detected before in humans, the official Chinese news agency Xinhua reported.
Both of those who died, men aged 27 and 87, lived in Shanghai, while a 35-year-old woman in Chuzhou city in nearby Anhui province is in the hospital, the Chinese National Health and Family Planning Commission said Sunday, according to Xinhua.
The victims all had initial symptoms of fever and coughing that then developed into severe pneumonia and difficulty in breathing, Xinhua reported. A team of experts assigned by the health commission established that the three cases were human infections of H7N9 avian influenza, which has not been found in humans previously, the news agency reported.
Investigators haven't yet figured out how the three people contracted the virus, according to the commission. It ruled out the theory that they had infected one another. None of the 88 people who had close contact with the victims have shown symptoms, it said, suggesting the virus isn't highly contagious among humans.
According to Xinhua, the 87-year-old man fell ill on February 19 and died on March 4; the 27-year-old man became unwell on February 27 and died on March 10; and the female victim got sick on March 9. The Chinese Center for Disease Control and Preservation on Friday separated the H7N9 bird flu virus from samples from the victims, Xinhua reported.
Because these three people are the only human cases of H7N9 detected so far, little research has been carried out on it, the news agency noted. There are no known vaccines against this virus, it said. The better known H5N1 avian flu virus has infected more than 600 people since 2003, of which 371 died, according to the World Health Organization (WHO).
In February, China reported two new human cases of H5N1 in the southern province of Guizhou, both of whom were in a critical condition, the WHO said.
A spike in H5N1 deaths, many of them children, has been reported in Cambodia, prompting concern among health authorities.