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Avian Influenza
Avian Influenza A (H7N9) Virus
Human infections with a new avian influenza A (H7N9) virus (“H7N9”) were first reported in China in March 2013. Annual epidemics of human infections with H7N9 viruses in China have been reported since that time. Studies indicate that avian influenza viruses, like seasonal influenza viruses, have a seasonal pattern: they circulate at higher levels in cold weather and at lower levels in warm weather. As of January 16, 2017[PDF - 382 KB, 9 pages], cumulative reported human infections with H7N9 totaled 918 with 359 deaths.
Most human infections with H7N9 have occurred after exposure to poultry; H7N9 viruses continue to circulate in poultry in China. Most reported patients have had severe respiratory illness; about one-third of patients have died. Rare, limited person-to-person spread of this virus has been identified in China, but there is no evidence of sustained person-to-person spread of H7N9. Some cases of H7N9 have been reported outside of mainland China but most of these infections have occurred among people who had traveled to China before becoming ill. H7N9 viruses have not been detected in people or birds in the United States.
It’s likely that sporadic human infections with H7N9 associated with poultry exposure will continue to occur in China. It's also possible that H7N9 may spread to poultry in neighboring countries and that human cases associated with poultry exposure may be detected in neighboring countries. It’s also possible that H7N9 cases may continue to be detected among travelers returning from H7N9-affected countries, even possibly in the United States. However, as long as there is no evidence of ongoing, sustained person-to-person spread of H7N9, the public health risk assessment would not change substantially.
Most concerning about this situation is the pandemic potential of this virus. Influenza viruses constantly change and it’s possible that this virus could gain the ability to spread easily and sustainably among people, triggering a global outbreak of disease (pandemic). In fact, of the influenza viruses rated by the Influenza Risk Assessment Tool (IRAT), H7N9 is ranked as having the greatest potential to cause a pandemic, as well as potentially posing the greatest risk to severely impact public health.
The U.S. Government supports international surveillance for H7N9 and other influenza viruses with pandemic potential. CDC is following the H7N9 situation closely and coordinating with domestic and international partners. Most important, CDC takes routine preparedness actions whenever a new virus with pandemic potential is identified, including developing candidate vaccine viruses to use for vaccine production in case vaccine is needed. Those preparedness measures continue. CDC also has issued guidance to clinicians and public health authorities in the United States, as well as provided information for people traveling to China. CDC will provide updated information as it becomes available.
Recently Reported
H7N9 Outbreak Characterization
What's New & Updated
H7N9: What should I do?
Avian Influenza A (H7N9) Virus
Human infections with a new avian influenza A (H7N9) virus (“H7N9”) were first reported in China in March 2013. Annual epidemics of human infections with H7N9 viruses in China have been reported since that time. Studies indicate that avian influenza viruses, like seasonal influenza viruses, have a seasonal pattern: they circulate at higher levels in cold weather and at lower levels in warm weather. As of January 16, 2017[PDF - 382 KB, 9 pages], cumulative reported human infections with H7N9 totaled 918 with 359 deaths.
Most human infections with H7N9 have occurred after exposure to poultry; H7N9 viruses continue to circulate in poultry in China. Most reported patients have had severe respiratory illness; about one-third of patients have died. Rare, limited person-to-person spread of this virus has been identified in China, but there is no evidence of sustained person-to-person spread of H7N9. Some cases of H7N9 have been reported outside of mainland China but most of these infections have occurred among people who had traveled to China before becoming ill. H7N9 viruses have not been detected in people or birds in the United States.
It’s likely that sporadic human infections with H7N9 associated with poultry exposure will continue to occur in China. It's also possible that H7N9 may spread to poultry in neighboring countries and that human cases associated with poultry exposure may be detected in neighboring countries. It’s also possible that H7N9 cases may continue to be detected among travelers returning from H7N9-affected countries, even possibly in the United States. However, as long as there is no evidence of ongoing, sustained person-to-person spread of H7N9, the public health risk assessment would not change substantially.
Most concerning about this situation is the pandemic potential of this virus. Influenza viruses constantly change and it’s possible that this virus could gain the ability to spread easily and sustainably among people, triggering a global outbreak of disease (pandemic). In fact, of the influenza viruses rated by the Influenza Risk Assessment Tool (IRAT), H7N9 is ranked as having the greatest potential to cause a pandemic, as well as potentially posing the greatest risk to severely impact public health.
The U.S. Government supports international surveillance for H7N9 and other influenza viruses with pandemic potential. CDC is following the H7N9 situation closely and coordinating with domestic and international partners. Most important, CDC takes routine preparedness actions whenever a new virus with pandemic potential is identified, including developing candidate vaccine viruses to use for vaccine production in case vaccine is needed. Those preparedness measures continue. CDC also has issued guidance to clinicians and public health authorities in the United States, as well as provided information for people traveling to China. CDC will provide updated information as it becomes available.
Recently Reported
- World Health Organization report: "Influenza at the human-animal interface: summary and assessment, 20 December to 16 January 2017"[328 KB, 9 pages]
- MMWR report: "Assessing Change in Avian Influenza A(H7N9) Virus Infections During the Fourth Epidemic — China, September 2015–August 2016."
H7N9 Outbreak Characterization
- H7N9 infections in people and poultry in China
- Sporadic infections in humans; many with poultry exposure
- No sustained or community transmission
What's New & Updated
H7N9: What should I do?
- CDC does not have any new or special recommendations for the U.S. public at this time regarding H7N9. CDC will keep you updated. Stay informed.
- Since H7N9 is not spreading easily from person to person at this time, CDC does not recommend that people delay or cancel trips to China. The World Health Organization also is watching this situation closely and does not recommend any travel restrictions.
- CDC advises travelers to China to take some common sense precautions, like not touching birds or other animals and washing hands often. Poultry and poultry products should be fully cooked. CDC will update its advice for travelers if the situation in China changes. This guidance is available at Avian Flu (H7N9) in China.
- Page last reviewed: January 27, 2017
- Page last updated: January 27, 2017
- Content source:
- Centers for Disease Control and Prevention, National Center for Immunization and Respiratory Diseases (NCIRD)
- Page maintained by: Office of the Associate Director for Communication, Digital Media Branch, Division of Public Affairs
- https://www.cdc.gov/flu/avianflu/h7n9-virus.htm