CDC FluView Week 37: Another Novel H1N2v Case Detected In Ohio

 

#16,211

Shiloh on FluTrackers picked up a local media report about an H1N2v case in Ohio this morning, and a short while ago it was confirmed in the CDC's weekly FluView Report, making this the 2nd time this year a resident of Ohio has been diagnosed with a swine variant (H1N2v) influenza infection.  

Last May (see CDC FluView Week 20: Novel H1N2(v) Influenza Infection Reported In Ohio) the virus was detected in a patient < 18  years of age, who lived on a farm where swine were present. 

While most swine variant infections can be traced to contract with pigs - either on farms or at agricultural exhibits - today's announced case does not appear to have had contact with swine, raising the possibility that it may have been transmitted from human-to-human. 

Although rare, we've seen other cases of limited H-2-H transmission with swine variants, and of course, the 2009 H1N1 swine flu was highly transmissible between humans. The CDC's risk assessment for Swine Variant 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 information provided in today's FluView

Novel Influenza A Virus

One human infection with an influenza A(H1N2) variant (A(H1N2)v) virus was reported by Ohio. The patient is <18 years of age, was not hospitalized, and has completely recovered from their illness. The patient and the household contacts of the patient report no swine contact or attendance at agricultural exhibits where swine were present. It is possible that limited human-to-human transmission occurred. No ongoing human-to-human transmission has been identified. This is the third influenza A(H1N2)v virus 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”. Ten human infections with a novel influenza A virus have been reported in the United States this influenza season, including two H3N2v (IA, WI), three H1N2v (IA, OH (2)), and five H1N1v (IA, NC, WI (3)) virus infections. Six infections have occurred in children <18 years of age and four have occurred in adults ≥ 18 years of age. Of the ten infected individuals, only one had no identified connection to swine. The other nine individuals had direct contact with swine, were on a property with swine present, or had a household member who had direct contact with swine 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 http://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. 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 

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.

Today's case is the 10th detected in the United States during the 2020-2021 flu season, although it is very likely that other cases have gone undetected. Most infections are mild, and most people will never be tested.

We've also seen sporadic human infections with swine variant viruses (H1N1v, H1N2v, H3N2v) around the world, with recent cases reported in France, Taiwan, Canada, Brazil, Germany, and the Netherlands.

For now, sporadic jumps of swine variant influenza from pigs to humans pose only a minor public health risk. But with every reassortment, and every species jump, these viruses are afforded new opportunities to overcome the barriers that have prevented them from becoming a pandemic strain. 

So we track them with understandable interest.