H3N2v Influenza A Virus (Seasonal Flu)

What is H3N2?

H3N2 is a subtype of the influenza A virus, the pathogen that causes the seasonal influenza. There are many subtypes of influenza A and H3N2 is one of them, just like H1N1 which caused the “swine flu” epidemic of 2009. Human H3N2 viruses are a common cause of the seasonal flu but now there is a new H3N2 variant which is also a “swine flu” virus. It causes the flu in pigs and was almost never seen in humans until recently. This H3N2 is associated with a more severe seasonal flu in humans these days, leading to complications, need for hospitalization and even deaths in high risk individuals.

What is H3N2v?

H3N2v is a variant of the virus which infects humans. Normally this type of H3N2 affects pigs but when it occurs in humans then it is called a variant virus and in this case marked as H3N2v. Although influenza A is the main cause of seasonal flu throughout the world, there are also other types known as influenza B and influenza C.

In terms of influenza A, there are different subtypes, some of which occur almost exclusively in certain mammals or birds, whiles other can affect multiple species. Influenza viruses mutate rapidly which is one of the reasons that a single vaccine is not effective every year. With the H3N2 variant, the virus has mutated where it is now able to infect humans. It has a combination of genes from viruses that affect bird, pigs and humans.

H3N2v Outbreak

Outbreaks of different subtypes of influenza A viruses have been causing panic throughout the world every few years. This is not a new phenomenon but is better understood in the past few decades due to advances in the medical sciences. In 2009 there was the H1N1 swine flu outbreak. The H3N2v virus was first discovered in 2010 and human infection was reported by 2011 in about 12 people in the United States. This number increased to 307 cases in July to November 2011.

It is mainly seen in people who have direct contact with pigs although a handful of cases due to human-to-human transmission have been reported. There is concern yet again that the H3N2v virus will be a more common cause of seasonal flu in the United States during the current flu season. According to the World Health Organization report in early January 2013, H3N2 was the predominant subtype  of influenza cases globally between December 9 to 22, 2012.

Flu Spread

The method of spread of H3N2v is not significantly different from other influenza virus strains. It occurs with infective droplets that is passed out into the environment from an infected person or animal. This can be through sneezing or coughing, although mucus secretions on the hands or on objects can also transmit the virus to an uninfected person. it is also possible that the infection can be contracted by inhaling dust containing the virus. H3N2v is transmitted from pigs to humans. It can also be spread back to pigs from humans.


Although uncommon it is possible that H3N2v is spread from person-to-person transmission. The rather limited spread from person-to-person thus far means that the H3N2v flu is actually less contagious that other strains and subtypes of the influenza virus. The main route of spread of H3N2v is from pigs to people. It is important to note that a person can still contract the H3N2v virus even if they do not have direct physical contact with pigs. The airborne droplets from pigs may linger in the air for long enough to infect passersby. Even without direct physical contact, a person would still nevertheless have to have close contact with infected pigs.

H3N2v Danger

The seasonal flu has probably been around for as long as humans have existed. It is not a new type of infection although the virus is rapidly mutating. The concern regarding the H3N2v flu is similar to that of the 2009 H1N1 flu outbreak. With regards to H3N2v, the virus may :

  • Lead to outbreaks at it spreads more easily to humans from pigs than other “swine flu” viruses.
  • Begin spreading from human-to-human with greater ease leading to community outbreaks.
  • Cause a more severe disease in some high risk individuals leading to a greater chance of hospitalization and even death.
  • Adversely affect children younger than 10 years who do not seem to have immunity to this subtype of the influenza A virus.

Any new strain of the flu virus that can cause a more severe disease may have detrimental effects on public health. It increases the chance of complications, need for hospitalization and deaths particularly in children and the elderly. The flu also has a significant impact on absenteeism and productivity which has a economic implication.

H3N2 Symptoms

The signs and symptoms of the H3N2 flu are similar to those of other strains causing the seasonal flu. In fact many people do not realize that they have been infected with the H3N2 strain.

  • Fever, often with temperatures exceeding 100F.
  • Chills.
  • Malaise – a feeling of being unwell.
  • Fatigue.
  • Runny nose, nasal congestion and sneezing.
  • Cough.
  • Sore throat.
  • Headaches.
  • Generalized body pains.

Gastrointestinal symptoms such as nausea, vomiting and diarrhea are more frequently seen in children and are uncommon in adults.

Influenza A H3N2 Tests

Usually diagnostic investigations are not required for the seasonal flu. Most doctors diagnose the flu based on the clinical presentation. However, when the flu is persistent, causing severe complications and there is concern about community outbreaks then further testing may be considered. This helps with identifying the exact virus causing the flu and also assists in determining the most effective vaccine to prevent new cases, or at least limit the severity of the illness.

A viral culture utilizes the nasal or throat secretions to “grow” the virus in a laboratory and then identify the exact strain. There are some rapid diagnostic tests available. However, these tests are not widely used since there are issues surrounding its sensitivity. It is also not widely available and the cost may not be warranted for an infection that is readily overcome by healthy individuals within a short period of time. The treatment for the flu is largely the same and therefore diagnosing the exact strain is not usually necessary.

H3N2 Treatment

H3N2 can be treated with antiviral drugs like oseltamivir (marketed as Tamiflu) and zanamivir (marketed as Relenza). These drugs inhibit viral replication. Recently oseltamivir has been approved for use in children younger than 1 years of age by the Food and Drug Administration (FDA) in the United States. Antiviral drugs are more effective if used in the early stages of the infection. However, it is the body’s immune system that is still the most effective means of combating the flu virus. Therefore overall health is important.

Most people do not receive specific treatment for the seasonal flu. The infection is short-lived and if properly managed in healthy individuals, it is unlikely to lead to complications. Supportive measures for the seasonal flu, irrespective of the strain, include :

  • Strict bed rest at least for the first few days when the symptoms are the most intense.
  • Plenty of water, preferably oral rehydrating solutions (ORS).
  • Proper nutrition in terms of a balanced diet. Bland foods may be better tolerated.
  • Good hygiene practices to avoid secondary bacterial infections.

H3N2 Vaccine

The research and development for flu vaccines are ongoing. Currently the World Health Organization (WHO) is recommending the use of vaccines containing influenza A H1N1 and H3N2 as well as influenza B strains. Although influenza A is the predominant type of virus responsible for the seasonal flu, over 20% of flu cases in the latter part of December 2012 were due to influenza B. The current vaccine used for the prevention of seasonal flu is still effective but recent reports from the Center for Disease Control (CDC) estimates that it is only 62% effective.

No flu vaccine is 100% effective as the virus mutates rapidly and certain people will still develop the flu even after being vaccinated. Nevertheless vaccination is recommended for every person, especially high risk groups such as children, pregnant women, people living with chronic illnesses and the elderly. Annual vaccination is important. Even if the vaccine does not prevent the flu, it does at least reduce the severity of the infection in vaccinated individuals.

H3N2 Prevention

Vaccination is still the most effective means of preventing the seasonal flu. It only becomes effective about 10 to 14 days after administration. Apart from vaccination, various preventative measures can be undertaken to avoid developing the flu or at the very least minimizing the risk of contracting the infection. This primarily revolves around limiting exposure to an infected person and maintaining a healthy immune system. However, with the H3N2v there is the added concern of contact with pigs. Therefore it is important to reduce contact with pigs where possible and avoid swine barns or styes. The CDC has provided recommendations to prevent the spread of flu between people and pigs.

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