November 1, 2021— Ongoing global monitoring for respiratory viruses with pandemic potential has recently identified three new human infections with avian influenza A(H5N6) virus (or “A(H5N6) bird flu”) in China. Reported influenza A(H5N6) virus iChina. nfections during 2021 have doubled the number of such cases detected since this virus was first found in people in 2014, raising concerns about the risk of additional human zoonotic infections and the pandemic potential of this virus. In coordination with the World Health Organization Global Influenza Program, CDC and global partners reviewed laboratory and epidemiologic data for influenza A(H5N6) viruses as well as existing H5 candidate vaccine viruses (CVVs) to assess their relatedness to current influenza A(H5N6) viruses during September 2021. Based on current antigenic, genetic and epidemiologic data, it was determined that previously recommended H5 CVVs are still expected to offer protection against influenza A(H5N6) viruses should vaccination be needed.

CDC takes routine public health preparedness measures whenever a virus with zoonotic or pandemic potential is identified. This includes conducting a risk assessment and, as appropriate, preparing CVVs that could be used to rapidly make vaccines if needed. CDC conducted a formal risk assessment of highly pathogenic influenza A(H5N6) viruses in April 2016 and determined that these viruses posed a moderate risk in terms of their potential to cause a pandemic as well as the potential to cause moderate public health impact if they were to spread person-to-person. Since the first identification of human infections with influenza A(H5N6) viruses in 2014, multiple H5 CVVs have been developed to cover different antigenic groups of these viruses. A new risk assessment of influenza A(H5N6) is currently underway. Analysis of influenza A(H5N6) viruses also shows that these viruses remain susceptible to influenza antiviral medications, such as the neuraminidase inhibitors (oseltamivir, zanamivir, peramivir) and polymerase acidic (PA) protein inhibitor (baloxavir), meaning that treatment options would be available.

Since 2014 when the first influenza A(H5N6) infection in a person was detected in China, 51 such infections have been reported, including 25 during 2021, as of October 29, 2021. Twenty-four of the 25 cases identified in 2021 were detected in  China and one was detected in Lao PDR. The case in Lao PDR was the first human infection with influenza A(H5N6) reportedexternal icon outside of China.

Most of the cases of influenza A(H5N6) reported in China during 2021 have had exposure to birds prior to illness onset. The three newest infections occurred in adults who, as of October 29, 2021, were reportedly hospitalized or in critical condition. There have been seven deaths (all in China) from influenza A(H5N6) this year. As of October 29, 2021, of the 51 laboratory-confirmed cases of human infection with influenza A(H5N6) virus reported to the World Health Organization since 2014, 25 infections resulted in death.

Avian influenza is a disease caused by infection with type A bird flu viruses. These viruses occur naturally among wild aquatic birds worldwide and can infect domestic poultry and other bird and animal species. Bird flu viruses do not normally infect humans. However, sporadic human infections with these viruses do occur. This is concerning because of the possibility that bird flu viruses could change and gain the ability to spread easily between people, with the potential to cause a flu pandemic; therefore, continued monitoring for human infections of bird flu and person-to-person spread is extremely important for public health.

Infected birds shed flu virus in their saliva, mucous and feces. Human infections with bird flu viruses can happen when enough virus gets into a person’s eyes, nose or mouth, or is inhaled. Influenza A(H5N6) was first detected in poultry in 2013 and has continued to spread among wild bird and poultry in many countries around the world. While rare human infections with this and other bird flu viruses have occurred most often after unprotected contact with infected birds or contaminated environments, some infections have been identified where direct contact with infected birds or contaminated surfaces was not known to have occurred.

These infections serve as a reminder of the importance of following CDC’s recommended prevention measures for people to take when around birds, especially when traveling to countries where bird flu is endemic in poultry and underscore the importance of ongoing pandemic preparedness measures.

CDC is continuing to monitor the situation and will provide updates as needed. The risk to the U.S. public from these viruses is currently considered to be low, but each case of human infection with a bird flu virus should be fully investigated to be sure that such viruses are not spreading person-to-person and to limit further exposure of humans to infected animals or environments. More information on bird flu can be found here.

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