#16,300
Today's CDC's weekly FluView Report contains details on three novel flu infections - all from the 2020-2021 flu season (which ended with week 39) - and all of them of swine origin. This brings to 14 the number of novel swine variant viruses reported during the 2020-21 influenza season, with 1 reported for the 2021-2022 season.
Most, but not all, of these cases had recent direct contract with pigs. It is likely that more cases occur than we know about, because testing for swine variant viruses isn't commonly done for mild flu. The CDC's risk assessment for Swine Variant viruses reads:
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).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
Today's FluView Update reads: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
Novel Influenza A Virus
Three human infections with novel influenza A viruses that occurred during the 2020-21 influenza season were reported. One human infection with novel influenza A(H1N2) variant (A(H1N2)v) was reported by Indiana and two human infections with influenza A(H1N1)v were reported by Iowa. All three patients were adults ≥ 18 years of age, were not hospitalized, and have recovered from their illness. All three patients had attended an agricultural event where swine were present and/or visited a farm where swine were present. No ongoing human-to-human transmission was identified associated with any of these patients.
During the 2020-21 influenza season, 14 human infections with a novel influenza A viruses were reported in the United States, including two H3N2v (IA, WI), four H1N2v (IA, IN, OH (2)), and eight H1N1v (IA (3), NC, ND, WI (3)) virus infections. During the 2021-22 influenza season, one human infection with a novel influenza A virus has been reported in the United States: H3N2v (OH).
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 close proximity 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 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.
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 it is incumbent upon us to monitor their evolution closely.
