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With the CDC's FluView map (above) looking more like early December than October, the 2022-2023 flu season appears to be well underway, particularly in the Southeast and South Central states.
Novel Influenza A Virus
A human infection with a novel influenza A virus was reported by the Michigan Department of Health and Human Services. The patient was infected with an influenza A(H3N2) variant (A(H3N2)v) virus. The illness occurred during week 36 of 2022. The patient is <18 years of age, was not hospitalized, and has recovered from their illness. An investigation by local public health officials found that the patient had indirect swine exposure at an agricultural fair prior to their illness onset. Additional investigation did not identify respiratory illness in any of the patient’s household contacts. No person-to-person transmission of A(H3N2)v virus associated with this patient has been identified.
A total of nine human infections with variant novel influenza A viruses have been reported in the United States in 2022, including four H3N2v (Michigan (1) West Virginia (3)) and five H1N2v (Georgia, Michigan, Ohio, Oregon, Wisconsin) viruses. When an influenza virus that normally circulates in swine (but not people) is detected in a person, it is called a “variant” influenza virus. Most human infections with variant influenza viruses occur following exposure to swine, but human-to-human transmission can occur. It is important to note that in most cases, variant influenza viruses have not shown the ability to spread easily and sustainably from person to person.
Early identification and investigation of human infections with novel influenza A viruses are critical so that the risk of infection can be understood, and appropriate public health measures can be taken.
Additional information on influenza in swine, variant influenza virus infection in humans, and guidance to interact safely with swine can be found at www.cdc.gov/flu/swineflu/index.htm.
Additional information regarding human infections with novel influenza A viruses:
Surveillance Methods | FluView Interactive
Although it is rare to see swine variant viruses spread efficiently in humans, and most cases are mild or moderate, the CDC's IRAT (Influenza Risk Assessment Tool) lists 3 North American swine viruses as having at least some pandemic potential (2 added in 2019).
H1N2 variant [A/California/62/2018] Jul 2019 5.8 5.7 ModerateH3N2 variant [A/Ohio/13/2017] Jul 2019 6.6 5.8 Moderate
H3N2 variant [A/Indiana/08/2011] Dec 2012 6.0 4.5 Moderate
The pandemic risk from swine variant viruses is low, but not zero, as these viruses continue to reinvent themselves as they circulate in pigs.
