Two men in Shanghai, China, have died after being exposed to a previously unknown bird flu strain.

According to Xinhua news, two men ages 27 and 87 fell ill with the H7N9 strain in February and died in March. A woman age 35 who contracted the virus is critically ill.

According to a statement from China's National Health and Family Planning Commission, it is unclear how the three became infected. However, all three showed the same symptoms of a high fever and cough, later developing into severe pneumonia and trouble breathing.

Should U.S. citizens be worried? There is no vaccine against the strain. However, the new type of H7N9 bird flu is considered to be a low pathogenic strain that humans cannot contract easily. The vast majority of human deaths caused by bird flu have been from the H5N1 strain. The commission has stated that it doesn't believe the strain is easily spread between humans. They cited the fact that 88 people in close proximity to the victims did not seem to have been infected.

A failed effort on the part of the Chinese to cover up SARS (severe acute respiratory syndrome) had previously aroused suspicion: something that continues now given the fact that the government waited 20 days to announce the deaths from H7N9. In response, the Chinese government said that since H7N9 was new, it hadn't yet been included in China's reporting system for infectious diseases, thereby making it take longer for authorities to pronounce the diagnostic results.

In response to the outbreak, medical experts have cautioned citizens to wash their hands more frequently and avoid contact with dead animals.