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H3N2v Influenza: Symptoms, Diagnosis, and Treatment

Published on Dec 16, 2022   -  4 min read


The H3N2v is a non-human influenza virus seen in pigs and can cause human infection. To know more, read the article below.


In 2010, the viruses were first identified in pigs in the United States. The name is derived from the forms of the two types of proteins on the surface of the virus coat, hemagglutinin (H) and neuraminidase (N). Influenza viruses are usually found in pigs and are known as “variant” viruses when transferred to people. In 2012, there was a massive outbreak of the H3N2v virus, with around 309 cases reported. The intermittent spread of the infection with the H3N2v virus has been witnessed since then. Infections with the H3N2v virus have primarily been associated with exposure to pigs at agricultural farms. The human-to-human transfer of this virus is not seen frequently in the past, and no community spread of H3N2v has been identified.

Approximately 36,000 people die yearly from seasonal influenza in the United States. Flu vaccines are developed based on which mutants of H1N1, H3N2, H1N2, and influenza B will proliferate in the next season. Different vaccines are designed for the Northern and Southern hemispheres for the upcoming annual epidemics. During the past ten years, H3N2 has dominated its prevalence over H1N1, H1N2, and influenza B.

What Is H3N2v Influenza?

The influenza H3N2 variant virus was first detected in July 2011 with the matrix (M) gene from the H1N1 pandemic virus. The virus that usually circulates in pigs is the “swine influenza virus.” However, when the virus infects humans, it is termed a “variant” virus.

In 1968 a variant or subtype of the H3N2 virus was introduced into the human population, leading to a global pandemic with around one million deaths worldwide. Since their evolution in 1968, H3N2 influenza viruses have undergone extensive genetic and antigenic changes and have caused various seasonal epidemics. The World Health Organization proposed changes in around 28 vaccine strains over that period. In addition, the H3N2 influenza viruses also have changed their receptor binding properties over the last fifty years and started displaying a reduced affinity for oligosaccharide analogs of cell surface receptors.

How Is H3N2v Transmitted?

The influenza virus can be transmitted from pigs to people. The spread of infection occurs through droplets inhaled through the mouth or nose. In some cases, the virus is transmitted by touching something that has it on it and then touching the mouth or nose with the same hand. The infection is common in people exposed to the virus on agricultural farms.

What Are the Symptoms of H3N2v Influenza?

The H3N2v influenza symptoms are similar to the symptoms of seasonal influenza, which include:

What Is the Treatment for H3N2v Influenza?

The drugs used to treat H3N3v influenza are the same as the ones used for seasonal flu. The commonly recommended drugs are Oseltamivir and Zanamivir. Initial treatment is essential and is important in people, especially with high-risk conditions. The H3N2v virus developed resistance to the standard antiviral drugs (Amantadine and Rimantadine), which was 1 % in 1994 and increased to 12 % in 2003 and 91 % in 2005.

How Is H3N2v Influenza Diagnosed?

The flu shows symptoms shared with other respiratory disorders, such as the cold. Therefore, it is impossible to know whether a person has the H3N2V flu just by observing the clinical symptoms. A healthcare professional should perform a laboratory test to confirm whether one has flu or other disorders. However, if flu-like symptoms are observed during the traditional flu season (October to May), then it can be diagnosed as the common flu even without the help of a laboratory test.

Which Vaccine Is Available for H3N2v Influenza?

Currently, no vaccine is available for H3N2v infection alone. Scientists are working towards the development of a vaccine. However, according to the Centers for Disease Control and Prevention, no decision has been made for the massive production of a vaccine. The vaccine for seasonal flu does not protect against H3N2v influenza. The Centers for Disease Control and Prevention states that children six months and older should get a seasonal flu vaccine annually.

The current vaccine is composed of three strains:

  • Two strains of Influenza A (H3N2 and H1N1).

  • One strain of Influenza B.

Immunization should be done for all patients over 65 years of age, those with chronic medical illnesses, and those who provide healthcare to patients. If the vaccine combats the circulating strain of flu, it can prevent disease in 70 % to 90 % of cases. Unfortunately, for older patients with chronic disease, the efficacy is less. However, the vaccine can still attenuate the influenza infection and lead to fewer lower respiratory tract infections and the associated morbidity and mortality that follow influenza.

The H3N2v influenza vaccine effectiveness study in the U.S. and Europe between the 2016 to 2017 seasons showed poor efficacy for all age groups. In addition, the rapid changes in influenza viruses make it difficult for experts to recognize and predict epidemiological threats in the future. Therefore, the World Health Organization meets every six months to decide which strains should be included in the seasonal influenza vaccine.

How Can H3N2v Influenza Be Prevented?

1) People who are at higher risk include:

  • Children younger than five years old.

  • People who are 65 years older.

  • Pregnant women.

  • People with comorbidities like asthma, diabetes, heart disease, weakened immune systems, and neurological or neurodevelopmental conditions.

2) Proximity or close contact with pigs should be avoided.

3) Toys, pacifiers, baby bottles, or similar items should not be taken to pig barns and arenas.

4) Mouth and nose should be covered while coughing or sneezing, and hands should be washed frequently.

5) Contact with pigs should be avoided if flu-like symptoms are present.

6) The use of gloves and masks should be encouraged if working in close proximity to pigs.

7) If flu-like symptoms are seen after exposure to pigs, the doctor should be consulted immediately.


The H3N2v viruses can replicate and transmit in mammals. The continued evolution of H3N2v in pigs may develop a novel virus to which most humans, especially older children and young adults, show no immunity. Improved investigations in pigs for new growing strains of H3N2v are essential. The cross-reactive antibody designs against the H3N2v virus are crucial in identifying the risks of viruses in humans, interspecies transmission, and their pandemic potential.

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Last reviewed at:
16 Dec 2022  -  4 min read




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