H3N2: What is it and why did it raise alarm in different parts of the world?

In the current context of respiratory diseasesthe influenza A H3N2 It has captured the attention of health authorities and international organizations due to its rapid expansion and its potential impact on public health.

During the winter season 2025-2026attention has been focused on a specific subclade known as H3N2 subclade Kcolloquially called “super flu”due to its high transmissibility and rapid spread in countries of Europe, United States and Canada.

Although many infections are mildsymptoms can be confused with other respiratory diseaseslike the covid-19so the authorities recommend perform diagnostic tests in case of doubt.

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Why is H3N2 considered alarming?

The health authorities maintain a high surveillance for several key reasons:

High transmissibility: the variant H3N2 subclade K has spread rapidly across several continents, bringing forward the usual flu season. The Pan American Health Organization (PAHO/PAHO) has noticed an increase in its circulation in Europe and Asia, which requires strengthening epidemiological surveillance and vaccination in America.

Accelerated spread and hospitalizations: Unlike other seasonal flus, this subclade has shown an early and sustained increase in cases. In countries like United Kingdomthe flu hospitalizations They grew significantly during the first weeks of December.

Greater impact on vulnerable groups: Although anyone can become infected, older adults, small children and people with chronic diseases have a higher risk of serious complications such as pneumonia or aggravation of pre-existing conditions.

Mutations and limited immune response: One of the most worrying factors is its ability to partially evade previous immunity. Experts explain that the virus mutations can make it difficult for immune system recognize it, even in people vaccinated or who have already had the flu.

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What symptoms does H3N2 flu cause?

Although the symptoms may seem similar to other flususually present in the form more sudden and intense. Among the most common are:

High fever, often higher than 38–39°C.
Persistent dry cough.
Nasal congestion and sneezing.
Muscle pain and headaches.
Extreme fatigue and general malaise.
Sore throat.
Loss of appetite.

What is the origin of the H3N2 virus?

The origin of H3N2 dates back to the beginning of the 2000s decadewhen he was identified in pigs. However, only years later could his behavior be thoroughly analyzed.

Key samples were collected in 2017and by sequencing its genome recently, scientists discovered that it did not match any known lineage of swine flu. It was a new variantresult of a jump of the virus from humans to pigs around the year 2002.

This finding confirms that the influenza virus they can cross speciesadapt and mutateincreasing the possibility of emergence variants with different characteristics.

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What does H3N2 mean?

The name H3N2 corresponds to a subtype of the Influenza A virus and refers to two proteins on its surface:

Hemagglutinin (H3)
Neuraminidase (N2)

These proteins are fundamental so that the virus enter cells and it propagate. The mutations in these structures can affect the way the immune system recognizes the virus.

Although the strain H3N2 —nicknamed by some specialists as “super flu”—has already been detected in Europethe first outbreaks were related to the influenza A H1N1from which this variant appears to have evolved.

How dangerous is the H3N2 flu?

Studies have identified mutations in key areas of hemagglutininwhich generates a significant antigenic shift. In simple terms, this means that the human immune system may not easily recognize the virus, even in people previously exposed to other influenza strains.

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What is the risk of H3N2 flu for Colombia?

According to the most recent report of the World Health Organization (WHO), South America remains under continuous surveillance.

In Colombiathe activity of the influenza A (H3N2) has been constant since the end of September 2025. However, the most evolved variant, the subclade Khad not been detected in the region until early November.

He December 12he National Institute of Respiratory Diseases (INER) confirmed the first case of influenza A H3N2 subclade K in Mexico, although it clarified that this finding does not represent a cause for alarm for the population.

Prevention and recommendations from authorities

Against this backdrop, health authorities insist on measures that have proven effective:

• Flu vaccination:
  It remains the most important preventive tool, especially for risk groups.
• Respiratory hygiene:
  Frequent hand washing, covering coughs or sneezes and avoiding closed or crowded places when symptoms are present.
• Early medical attention:
  Consulting a health professional for persistent or severe symptoms reduces the risk of complications.

Although he H3N2 is not a new virus, its current behavior and the appearance of the K subclade have raised eyebrows. global health alerts. In Colombia and the region, the epidemiological surveillancethe vaccination and the early detection They will be key to avoiding a greater impact on public health during the season.