As health officials continue to investigate the new H10N8 bird flu strain, the more dominant H7N9 strain has infected another 11 people in China, according to a report from the Xinhua News Agency.

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The deadly virus has left eight of 11 patients in critical condition, according to Chinese health authorities across four regions.

Despite the spike in illnesses — two 5 year olds are among the newly ill — health officials reaffirmed that there is no proof of the strain spreading person to person. Most cases have been isolated so far. Health authorities continue to try and identify H7N9 cases early, a strategy that the U.S. Centers for Disease Control and Prevention has also recommended to American doctors examining patients returning from China.

Since last year, all strains of bird flu have rarely infected people outside of China, but the H5N1 strain recently caused its second bird flu death in Vietnam, according to French news agency Agence France-Presse. Both deaths occurred in January.

The two dominant strains, H5N1 and H7N9, have caused hundreds of cases since 2003. Recently, a new strain, H10N8, killed its first human victim, a development the World Health Organization called “worrisome.”

Human infection from the virus occurs after direct contact with an infected animal. Although those in China should exercise caution with poultry, the threat for a pandemic is relatively small without human-to-human transmission.

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