H7N9: Frequently Asked Questions
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- What is H7N9?
- How many people have been infected with this H7N9 virus and how many have died in China since 2013?
- What is known about 5th epidemic of H7N9 virus in China?
- How has the H7N9 virus situation developed and changed in China since 2013?
- How do people get infected with bird flu viruses, including H7N9 virus?
- Is infection with this virus serious?
- What are the signs and symptoms of illness with H7N9 virus infection?
- Is this virus spreading from person-to-person?
- Is it possible that this virus will spread from person-to-person?
- Is there a vaccine to protect against H7N9 virus?
- Are there medicines to treat illness associated with this virus?
- What is the risk from this virus in the United States right now?
- Is it possible that human cases of H7N9 will be found in the United States?
- How are H7N9 virus infections diagnosed in people?
- Does CDC recommend that people delay or cancel trips to China because of H7N9 virus?
- What advice does CDC have for people traveling to China?
- Should travelers to China get a prescription for antivirals before their trip?
- What advice does CDC have for people in the United States with regard to H7N9?
- Is CDC worried that an H7N9 pandemic will start?
- What is CDC doing in response to H7N9?
Note: The content of this webpage will continue to be updated as CDC learns more about the ongoing H7N9 virus situation in China.
Since 2013, H7N9 virus infection has been found in birds and people in China. While the H7N9 virus continues to spread in poultry with sporadic human infections, no ongoing person-to-person spread of this virus has been found at this time. Here are some common questions and answers about H7N9 virus.
“H7N9” is a subtype of influenza A viruses that is sometimes found in birds, but that does not usually infect humans. Like all influenza A viruses, there are many different strains of H7N9 virus. Many H7 virus have circulated in poultry for centuries. Beginning at the end of March 2013, China reported the first known cases of zoonotic infections with a new strain of H7N9 virus that was very different from previously known H7N9 viruses. The virus was found to be circulating in poultry in the area. Since 2013, H7N9 viruses have continued to cause infections of poultry in China, with associated annual increases in the number of human infections with H7N9 viruses during the fall, winter, and spring months. China is currently experiencing its 5th epidemic of human infections with H7N9 virus during 2016-2017. Most human cases of H7N9 virus infection have been reported from eastern China (south to north), but cases also have been reported from northwestern China. Human cases of H7N9 virus infection acquired in China also have been identified in Taiwan, Malaysia and Canada.
Since 2013, the World Health Organization has reported 1,223 human infections with the H7N9 virus in China, as of a WHO report dated February 20, 2017. About 40% of those infected have died (note: reporting of deaths associated with H7N9 virus infection generally lag behind case reports). Numbers of reported human cases of H7N9 virus infection by annual epidemic are listed as follows:
- 1st epidemic: 135 cases;
- 2nd epidemic: 320 cases;
- 3rd epidemic: 226 cases;
- 4th epidemic: 123 cases;
- 5th epidemic: ongoing (424 human infections as of February 20, 2017).
From October 2016 to February 14, 2017, China reported 424 human infections with H7N9 virus to the World Health Organization. The most recent cases are described in a WHO report dated February 20, 2017. Since December 2016, there has been a large increase in H7N9 virus infections identified in people in China. This recent increase in cases during the 5th epidemic is consistent with the annual winter increase in H7N9 cases that has been observed in China since 2013.
On February 10, 2017, the World Health Organization posted a new scientific assessment regarding H7N9 viruses in China. Surveillance and epidemiological investigations in China have not detected any significant changes in the demographics of human H7N9 cases, the proportion of cases exposed to poultry, the number and size of clusters of H7N9 cases, or the case-fatality proportion when compared to prior H7N9 epidemics. There is currently no evidence of sustained person-to-person spread of H7N9 virus in China or anywhere else. The World Health Organization provides updates on the reported number of human cases of H7N9 virus infection on its website.
In December 2016, U.S. CDC and the Chinese CDC published a collaborative study regarding the H7N9 virus outbreaks in China during the first four annual epidemics. The study assessed what public health experts have learned about the H7N9 virus and how the situation has changed since human infections were first identified in early 2013. Looking at the annual epidemics from an epidemiological standpoint, H7N9 virus infections of humans have expanded to affect a larger geographic area of China. During the 4th epidemic, more cases of H7N9 virus infection were reported in people living in rural areas. Also during the 4th epidemic, public health researchers observed an increase in the proportion of people who became severely ill. People with H7N9 virus infection were significantly more likely to develop pneumonia and be admitted to an intensive care unit (although they were not more likely to die) than in past epidemics. Also, the 4th epidemic lasted longer than the previous three epidemics.
However, some aspects of the H7N9 situation in China have remained consistent to date. There has been no evidence of increased person-to-person transmission of H7N9 virus. In addition, the age and gender distribution of patients and the history of exposure (primarily recent exposure to live poultry, including by visiting a live poultry market) have remained consistent. Analysis of the genetic properties of H7N9 viruses looking for adaptations that would result in antiviral resistance or adaptation to more easily infect mammals indicates that recent H7N9 viruses are similar to what has been observed for H7N9 viruses throughout the four previous epidemics. Researchers are continuing to monitor the genetic properties of H7N9 viruses during the current 5th epidemic to look for changes.
The H7N9 virus continues to have the greatest potential to cause a pandemic of known emerging influenza A viruses, and H7N9 viruses are considered to be the influenza A virus with the greatest potential public health impact (i.e., the potential severity of human disease caused by the virus), according to CDC’s Influenza Risk Assessment Tool (IRAT). As a result, CDC, China and global health partners will continue to closely monitor the H7N9 virus situation in China and will continue to conduct risk assessments as the situation evolves.
Human infections with bird flu viruses are rare, but have happened in the past, usually after close contact with infected birds (both live and dead) or exposure to environments contaminated with bird flu virus, such as visiting a live poultry market.
Infected birds can shed a lot of bird flu viruses, for example, in their droppings or their mucus. If someone touches an infected bird or an environment contaminated with virus and then touches their eyes, nose or mouth, they may be infected with bird flu virus. There is some evidence that infection may also occur if the flu virus becomes aerosolized in contaminated material, such as when an infected bird flaps its wings. If someone were to breathe in airborne virus, it’s possible they could get infected.
Poultry infected with H7N9 virus do not experience any illness signs or symptoms. H7N9 virus-infected poultry are well-appearing, but transmission to humans can occur. H7N9 virus has been found in birds (poultry) and contaminated environments in China in some of the same areas where human infections have happened. Available evidence suggests that most people have been infected with H7H9 virus after having contact with infected poultry or contaminated environments, including visiting a live poultry market.
Most of the reported human cases H7N9 virus infection have had very serious illness, including severe pneumonia, and about 40% of reported human cases have resulted in death. However, there also are a small number of reports of milder human illness and one possible report of a person who tested positive for H7N9 virus who did not have any symptoms.
Signs and symptoms of H7N9 virus infection in people have started with high fever and cough. A lot of the cases have progressed to very serious illness, including severe pneumonia, acute respiratory distress syndrome (ARDS), septic shock and multi-organ failure leading to death.
China has conducted extensive case investigations of people infected with H7N9 virus and their close contacts and has found no evidence of "sustained" person-to-person spread at this time. Ongoing spread of a virus among humans is necessary for a pandemic to occur. However, a small number (approximately 7%) of confirmed H7N9 cases in China have occurred in small clusters, and some cases were associated with likely limited, non-sustained person-to-person spread of H7N9 virus. "Limited" virus spread usually refers to when a virus from an animal host infects a person and then spreads to a caretaker or close contact of that person but not any further. Based on what we know about other avian influenza viruses, some limited, non-sustained person-to-person spread of H7N9 virus is not surprising. Limited person-to-person spread of other avian influenza viruses is thought to have occurred rarely in the past in several countries, most notably with avian influenza A(H5N1) virus infection, following prolonged, close, unprotected exposure to a very sick patient. This highlights the importance of good infection prevention and control measures for hospitalized patients with H7N9 virus infection. CDC expects that additional limited person-to-person transmission events with the H7N9 virus could occur in the future if the virus continues to spread between birds and people. CDC and global public health experts are monitoring H7N9 viruses in China for changes that could allow them to spread more easily among people.
Yes. Based on what we know about human infections with other bird flu viruses, it’s possible and even likely that there will be some limited, non-sustained person-to-person spread of H7N9 virus. The important factor will be to determine whether H7N9 viruses gain the ability to spread easily from one person to another. Sustained person-to-person spread of a novel influenza A virus is needed for a pandemic to start. Health officials are watching the situation closely for this.
There currently is no publicly available vaccine to protect against H7N9 virus infection. CDC has worked closely with the World Health Organization and public health partners to develop three vaccine candidate viruses (CVVs) that could be used to make a vaccine against H7N9 virus, in the event of an influenza pandemic. These CVVs were developed to be similar to the H7N9 viruses that circulated in China during the 4th epidemic and are continually compared to new H7N9 viruses in China as they are discovered and reported. As part of pandemic preparedness activities, the U.S. Government purchased and stockpiled limited quantities of H7N9 vaccine produced from these CVVs to be used in case of an emergency. CDC and our partners continue to analyze representatives of the H7N9 viruses circulating during the 5th epidemic in China for changes that indicate a new CVV should be created.
CDC recommends oral oseltamivir (available as a generic version or under the trade name Tamiflu®), inhaled zanamivir (trade name Relenza®) and intravenous peramivir (trade name Rapivab®) for treatment of H7N9 virus infection. Most of the H7N9 viruses that have been studied appear to be susceptible (sensitive) to the three influenza antiviral drugs that are recommended in the treatment of seasonal influenza. Those drugs are oseltamivir, zanamivir and peramivir (neuraminidase inhibitors). Like seasonal influenza viruses, avian A(H7N9) viruses are resistant to the influenza antiviral drugs known as the adamantanes.
It’s important to note that all influenza viruses are evolving and may acquire genetic changes which can make one or more influenza antiviral drugs less effective. This happens with seasonal influenza viruses and could happen with H7N9 viruses in the future. As new H7N9 virus isolates are received, CDC conducts ongoing testing to determine the susceptibility of other H7N9 viruses to existing antiviral drugs. More information about antiviral resistance is available at Influenza Antiviral Drug Resistance: Questions & Answers.
No H7N9 virus infections of humans or birds have been detected in the United States. At this time, the risk to people in the United States is considered to be very low.
Yes. The most likely scenario for this right now would be H7N9 virus infection in a traveler from China. Many people travel between China and the United States. Human cases of H7N9 virus infection acquired in China have been reported in Taiwan and Malaysia, and in 2015, H7N9 virus infection was reported in Canada in two persons who had returned from travel to southern China. In January 2016, CDC issued a travel notice for people traveling to and from China that provides preventive actions people can take to protect themselves against H7N9 virus infection. CDC has issued guidance for isolating, testing, and treating such patients. However, since H7N9 virus does not efficiently spread from person-to-person, a few cases in the United States with travel links to China would not change the risk of H7N9 virus infection for the general public in the United States.
Check Avian Influenza A (H7N9) Virus for the latest guidance and situation updates on these viruses.
- For patients with suspected H7N9 virus infection, health care providers should refer to the CDC case definitions guidance for testing and treating patients with confirmed and probable H7N9 infections, and infection control guidance for health care facilities.
There are currently no tests available over the counter or at a doctor’s office that can quickly detect and distinguish between infection with H7N9 virus and other seasonal influenza A viruses. However, a more sophisticated test that specifically detects H7N9 virus has been developed by CDC for use by qualified public health laboratories in the United States and internationally. This test involves collecting a respiratory tract (i.e., nose, throat, lung) sample from a sick patient. The sample is then sent to a public health laboratory where testing known as rRT-PCR (real-time reverse transcription polymerase chain reaction) is conducted. rRT-PCR is very accurate and sensitive at detecting influenza viruses. This procedure typically provides results within 4 hours; however, the time involved in processing and reporting results may vary depending on the laboratory.
Since H7N9 virus 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.
The majority of human infections with H7N9 virus have occurred following direct or close exposure to infected poultry, including well-appearing chickens, or environments contaminated by poultry, such as visiting a live poultry market. Therefore, CDC advises travelers to China to take some common sense precautions, like not touching birds or other animals and washing hands often, and avoiding live poultry markets. 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.
At this time, CDC does not recommend prescribing antiviral drugs for prevention or self-treatment of H7N9 virus infection. CDC recommends that travelers to China follow common sense precautions to protect themselves and monitor their health during and after their trip. Anyone with fever, coughing, or shortness of breath within 10 days of traveling to China should see a doctor and tell the doctor about the recent travel to China, and if they have had any exposure to poultry.
There has not been any H7N9 virus infections of people or birds identified in the U.S. to date. CDC does not have any new or special recommendations for the U.S. public at this time regarding H7N9, except for those planning travel to China.
It is concerning whenever a new influenza A virus subtypes (e.g., H7N9) emerge that infects humans and causes severe illness. CDC considers the ongoing epidemics of H7N9 virus infections in China to be a serious public health situation; however, the current risk to the U.S. general public’s health is considered to be low. Since the emergence of the H7N9 virus in China in 2013, CDC and its public health partners have closely monitored the H7N9 virus and its spread in China. To date, H7N9 viruses have not demonstrated the ability to spread easily from person to person. If the H7N9 virus were to change and gain this ability, it’s possible that a pandemic (i.e., a global outbreak of disease) could occur. CDC has taken and continues to take steps to prepare for that possibility.
CDC is following this situation closely and coordinating with domestic and international partners, including China CDC and the World Health Organization.
In addition, CDC has taken and continues to take routine preparedness measures, including:
- CDC routinely examines the genetic sequences of H7N9 viruses as they become available.
- Sequences of H7N9 viruses isolated during the 4th epidemic in China during 2016 did not show any notable genetic changes. (A December 2016 report in CDC’s MMWR describes the 4th wave of H7N9 virus in China.)
- However, some of the recently available 5th epidemic sequences show new genetic changes in some of the viruses identified in humans, which could impact antigenicity or other characteristics.
- Further genetic and antigenic characterization of 5th epidemic viruses is ongoing at CDC.
- CDC has previously developed three H7N9 candidate vaccine viruses (CVVs) that could be used to make vaccine if it becomes necessary. These CVVs are similar to viruses that circulated in poultry during the fourth H7N9 epidemic in China.
- CDC is examining H7N9 viruses from the current 5th epidemic to consider whether an updated candidate vaccine virus needs to be created.
- CDC also will test 5th epidemic H7N9 viruses to see whether they remain susceptible to the antiviral drugs classified as neuraminidase inhibitors (i.e., oseltamivir, zanamivir and peramivir).
- CDC has previously developed and distributed a test kit that can detect H7N9 virus and that can be used by other public health laboratories.
- CDC has conducted and continues to conduct animal studies to learn more about the severity of disease associated with H7N9 virus and how the virus spreads.
- CDC has previously conducted studies on blood samples to see whether there is any existing immunity to H7N9 virus in the population.
- CDC continually gathers information to make a thorough public health risk assessments of H7N9 viruses in China. CDC uses the Influenza Risk Assessment Tool (IRAT) to assess the potential pandemic risk posed by influenza A viruses that currently circulate in animals but not in humans. CDC has used the IRAT to evaluate H7N9 viruses in the past. The IRAT is an iterative process, and CDC will revisit the results of the H7N9 IRAT scores (completed in 2016) as new information becomes available.
This is an evolving situation and CDC is working to learn more.
- Page last reviewed: February 23, 2017
- Page last updated: February 23, 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