#17,974
While the continued spillover of HPAI H5 into mammals has garnered most of our attention this week, the CDC is reporting in today's weekly FluView the first confirmed swine variant (H1N2v) human infection of 2024 in the United States.
Over the past dozen years we've seen roughly 500 swine variant cases (H1N1v, H1N2v, H3N2v) reported by the CDC, and last summer the CDC held a webinar for clinicians on recognizing, treating, and reporting zoonotic influenza cases in the community (see COCA Call : What Providers Need to Know about Zoonotic Influenza).
The CDC describes Swine Variant viruses in their Key Facts FAQ.
What is a variant influenza virus?
When an influenza virus that normally circulates in swine (but not people) is detected in a person, it is called a “variant influenza virus.” For example, if a swine origin influenza A H3N2 virus is detected in a person, that virus will be called an “H3N2 variant” virus or “H3N2v” virus.
Details on this latest case follow:
Novel Influenza A Virus:
A human infection with a novel influenza A virus was reported by the Pennsylvania Department of Health. The patient was infected with an influenza A(H1N2) variant (A(H1N2)v) virus. The patient is < 18 years of age, sought healthcare during the week ending March 9, 2024 (week 10), was hospitalized, and has since recovered.
An investigation by local public health officials found that the patient had swine contact prior to their illness onset. Additional investigation identified mild illness in two of the patient’s close contacts who also had contact with swine, that began prior to the patient’s onset of symptoms. No person-to-person transmission of A(H1N2)v virus associated with this patient has been identified. The investigation is ongoing. This is the first human infection with a variant influenza A virus reported in the United States in 2024.With few exceptions (i.e. the 2009 H1N1 pandemic virus), current swine influenza viruses don't appear to spread efficiently in humans. That said, 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).
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
H1N2 variant [A/California/62/2018] Jul 2019 5.8 5.7 Moderate
H3N2 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
In recent years we are seeing a rise in H1N2v infections, while prior to 2017 H3N2v was the most commonly reported swine variant virus. The CDC currently ranks a Chinese Swine-variant EA H1N1 `G4' as having the highest pandemic potential of any flu virus on their list.
While Swine-variant (typically H1N1v, H1N2v, H3N2v) infections are generally mild, the CDC routinely advises those who are at higher risk of serious flu complications (including children under 5, adults over 65, pregnant women, and those with certain chronic medical conditions), to avoid pigs and the swine barn altogether.But, as with avian flu, they all have barriers they must overcome.
Some recent blogs on swine variant viruses include:
Virology: Novel Influenza A Viruses in Pigs with Zoonotic Potential, Chile
Virologica Sinica: The Evolution, Pathogenicity & Transmissibility of Quadruple Reassortant H1N2 Swine Influenza Virus in China
WHO Update & Risk Assessment: H1N1v Case In Brazil
Eurosurveillance: A Case of Swine Influenza A(H1N2)v in England, November 2023
