Friday, June 04, 2021

CDC FluView Week 21: Novel H1N1(v) Influenza Infection Reported In Iowa


For the second week in a row, and for the 4th time in 2021, the CDC is reporting on a novel flu infection; this time involving a swine variant A(H1N1)v virus reported in a patient younger than 18 years old in Iowa.  

As is frequently the case, this patient only had mild symptoms - was not hospitalized - and had swine exposure at a farm.

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 website 
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 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 
But the most worrisome swine variant strain in the world today is found mostly in China, with  the CDC currently ranking their Swine-variant EA H1N1 `G4' as having the highest pandemic potential of any flu virus on their list. 

Today's report from the CDC's FluView follows:

Novel Influenza A Virus

One human infection with an influenza A(H1N1) variant (A(H1N1)v) virus was reported by Iowa. The patient is >18 years of age, was not hospitalized, and has completely recovered from their illness. Investigation into the source of the infection revealed that the patient works on a farm with swine present. No human-to-human transmission of A(H1N1)v virus has been identified associated with this patient. This is the second influenza A(H1N1)v virus infection identified in the United States that occurred in 2021.

When an influenza virus that normally circulates in swine (but not people) is detected in a person, it is called a “variant influenza virus”. Five human infections with a novel influenza A virus have been reported in the United States this season, including one H3N2v (WI), one H1N2v (OH), and three H1N1v (IA, NC, WI) infections. Three infections have occurred in children <18 years of age and two have occurred in adults ≥ 18 years of age. All cases either had direct contact with swine or lived on a property with swine present.

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 infection in humans, and strategies to interact safely with swine can be found at Additional information regarding human infections with novel influenza A viruses can be found at

For additional background, you may wish to revisit these past blogs on swine variant influenza.