Summary
The Centers for Disease Control and Prevention (CDC) is issuing this Health Alert Network (HAN)
Health Advisory to provide updates on recent variant1 influenza virus infections and summarize
CDC’s recommendations for identification, treatment, and prevention of variant influenza virus
infection for the summer and fall of 2022.
Background
Five cases of human infection with influenza viruses that usually spread only in pigs, also known as
variant influenza virus infections, were reported to CDC in August 2022. These cases include three
infections with influenza A(H3N2) variant (A(H3N2)v) virus and two infections with influenza A(H1N2)v
virus. These cases were identified in West Virginia (3), Oregon (1), and Ohio (1). Four of the five
cases reported exposure to pigs or attendance at an agricultural fair prior to illness, and one reported no
contact with pigs or attendance at an agricultural fair prior to illness. Clinical characteristics of these
cases have been similar to those of seasonal influenza infections and have included fever, cough,
pharyngitis, myalgia, and headache. No hospitalizations or deaths have occurred among these five
cases, and all patients are recovering or have recovered from their illnesses. To date, no person-toperson
spread associated with the five recent variant influenza virus infections has been identified.
Early identification and investigation of variant influenza virus infections are important to determine
whether the virus is spreading efficiently among people. Rapid detection and characterization of novel
influenza A viruses and efforts to reduce transmission to other people remain important components
of national efforts to prevent the emergence of new viruses that could have pandemic potential. To
accomplish this, testing for influenza viruses and monitoring for novel influenza A virus infections ,
including variant influenza virus infection, should continue year-round. Individuals, especially those
at increased risk of influenza complications, can take public health measures to limit their risk of
infection (e.g., limiting exposure to infected animals). Clinicians are encouraged to consider variant
influenza virus infection as a possible diagnosis when evaluating patients with acute respiratory
illnesses and exposure to pigs or agricultural fairs prior to illness.
Since 2005, 504 variant influenza virus infections (of different influenza A virus subtypes) have been
identified in the United States; most of these infections have been associated with exposure to pigs
or attendance at an agricultural fair prior to illness onset. Agricultural fairs occur across the United
States each year, primarily during the summer and early fall. Many fairs have swine barns, where
pigs from different geographic locations come in close contact with each other and with people.
These venues may allow influenza viruses to spread among pigs and between pigs and people.
Infected pigs may spread influenza viruses even if they are not symptomatic (e.g., coughing or
sneezing).
CDC anticipates that state health departments may identify more cases of infection with variant
influenza viruses in 2022 as the agricultural fair season continues. Testing for variant influenza
viruses should focus primarily on persons with exposures known to be associated with variant
influenza virus infection (e.g., agricultural fair attendance or workers in the swine industry). Novel
influenza A virus infections, which include those caused by variant influenza viruses, are notifiable
conditions in the United States, and all confirmed cases should be reported to CDC within 24 hours.
Recommendations for Clinicians
• Outside of the traditional influenza season, ask patients with suspected influenza if they have any
recent exposure to swine.
• Clinicians who suspect influenza in persons with recent exposure to swine should:
o Obtain a nasopharyngeal swab or aspirate from the patient,
o Place the swab or aspirate in a viral transport medium, and
o Contact their state or local health department to arrange transport and request a
timely diagnosis at a state public health laboratory.
• Recommend antiviral treatment in patients with suspected or confirmed variant influenza
virus infection who are hospitalized, have severe illness, or are in a group considered at
increased risk for complications from influenza2. Antiviral treatment can also be considered
for those not at increased risk based on clinical judgement and if treatment can be initiated
within 48 hours of illness onset.
Recommendations for Public Health Departments and Laboratorians
• Enhance surveillance for respiratory illness during agricultural fair season to facilitate timely
detection and investigation of variant influenza virus cases.
• Respiratory specimens from persons suspected to have variant influenza A virus infection should
be collected and sent for subtype-specific real-time polymerase chain reaction (RT-PCR) testing
at a state public health laboratory. While commercially available rapid influenza diagnostic tests
(RIDTs) and molecular assays for influenza can reliably detect variant influenza A viruses, they
cannot differentiate variant influenza A viruses from human influenza A viruses.
• Public health laboratories should immediately send influenza A virus specimens that cannot be
subtyped or are presumptive variant influenza positive (using methods as outlined in the assay’s
Instructions for Use) to CDC and submit all specimens that are otherwise unusual as soon as
possible after identification. Please email flusupport@cdc.gov to alert CDC that you have a
specimen to submit.
Recommendations for the Public
• Persons who are at higher risk for influenza complications2 should avoid exposure to pigs
and swine barns at fairs this year. If you cannot avoid exposure to pigs, you should wear a wellfitting
mask that covers the nose and mouth and should perform hand hygiene frequently.
o All persons should take precautions when engaging in activities that may involve
swine contact. Precautions include hand hygiene before and after exposure to
animals, avoiding eating or drinking in animal areas, and avoiding close contact with
animals that look or act ill.
• Patients with influenza-like illness who are at higher risk for influenza complications2 should
see their healthcare provider as soon as possible after symptom onset to determine if
treatment with antiviral medications is warranted.
o Patients who experience influenza-like symptoms following direct or close contact
with pigs and who seek medical care should inform their health care provider about
the exposure.
For More Information
• Influenza A (H3N2) Variant Virus
• Interim Information for Clinicians about Human Infections with H3N2v Virus for State and
Local Health Departments
• Prevention Strategies for Seasonal and Influenza A(H3N2)v in Health Care Settings
• Interim Guidance on Specimen Collection, Processing, and Testing for Patients with Suspected
Influenza A (H3N2)v Virus Infection for Public Health Professionals
• Testing, Reporting, and Control Strategies
• People at Higher Risk of Flu Complications
1Influenza viruses that circulate in swine are called swine influenza viruses when isolated from swine but are called variant
viruses when isolated from humans.
2This includes persons with certain underlying chronic medical conditions such as asthma, diabetes, heart disease, or
neurological conditions, pregnant people, and persons 5 years and younger and 65 years and older, or who have
weakened immune systems.
The Centers for Disease Control and Prevention (CDC) protects people’s health and safety by preventing
and controlling diseases and injuries; enhances health decisions by providing credible information on
critical health issues; and promotes healthy living through strong partnerships with local, national, and
international organizations.