For the 6th & 7th time in the 2020-21 flu season the CDC is reporting on novel flu infections, this time involving a swine variant A(H1N2)v virus contracted by two patients younger than 18 years old in Wisconsin.
Both attended the same county fair where swine were exhibited.
While most swine variant infections don't appear to transmit well in humans, more than 470 cases have been reported in the United States since 2005, including clusters of limited H-2-H transmission.
The CDC's Risk Assessment for these viruses reads:
Sporadic infections and even localized outbreaks among people with variant influenza viruses may occur. All influenza viruses have the capacity to change and it’s possible that variant viruses may change such that they infect people easily and spread easily from person-to-person. The Centers for Disease Control and Prevention (CDC) continues to monitor closely for variant influenza virus infections and will report cases of H3N2v and other variant influenza viruses weekly in FluView and on the case count tables on this websiteThe 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 ModerateH3N2 variant [A/Indiana/08/2011] Dec 2012 6.0 4.5 Moderate
Today's report from the CDC's FluView report follows:
Two human infections with a novel influenza A virus were reported by Wisconsin. Both individuals were infected with influenza A(H1N2) variant (A(H1N2)v) virus. Both patients were ≥18 years of age. One patient was hospitalized, and both have completely recovered from their illness. Investigation into the source of the infections revealed that prior to illness onset both patients attended the same county fair where swine were being exhibited. No human-to-human transmission of (A(H1N2)v) virus associated with either patient has been identified.
When an influenza virus that normally circulates in swine (but not people) is detected in a person, it is called a “variant influenza virus”. Seven human infections with a novel influenza A virus have been reported in the United States this influenza season, including one H3N2v (WI), three H1N2v (OH, WI (2)), and three H1N1v (IA, NC, WI) virus infections. Three infections have occurred in children <18 years of age and four have occurred in adults ≥ 18 years of age. All cases either had direct contact with swine or were on a property with swine present prior to illness onset.
Early identification and investigation of human infections with novel influenza A viruses are critical so that the risk of infection can be more fully understood and appropriate public health measures can be taken. Additional information on influenza in swine, variant influenza virus infection in humans, and strategies 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 can be found at https://gis.cdc.gov/grasp/fluview/Novel_Influenza.html.
The risk of one of these swine variant viruses sparking a pandemic is relatively low, but it isn't zero. A swine-origin H1N1v virus jumped to humans and sparked a mild-to-moderate flu pandemic in 2009, and the CDC currently ranks a Chinese Swine-variant EA H1N1 `G4' as having the highest pandemic potential of any flu virus on their list.
After a year without appreciable seasonal influenza - and community immunity to seasonal influenza presumably waning with each passing month - there are many who worry that we could be unusually vulnerable when influenza (novel or seasonal) finally does return.
A few other recent studies on swine-origin influenza include:
