Who is Subclade K of Influenza A(H3N2) and Why is it Circulating More?
The Pan American Health Organization (PAHO) reported that subclade K, also known as J.2.4.1, has shown rapid growth in Europe and several Asian countries, representing a significant proportion of the analyzed viruses. The United States and Canada also show a sustained increase.
Experts indicate that this is part of the natural evolution process of the seasonal virus. Although it has genetic variations compared to previous variants, no significant changes in severity or unusual increases in hospitalization or mortality have been documented.
Historically, seasons dominated by A(H3N2) tend to affect adults more severely, so PAHO emphasizes maintaining high vaccination coverage.
Is There Cause for Concern in Mexico?
As of December 11, Mexico had not reported any cases. However, on December 12, the first case was confirmed by the National Institute of Respiratory Diseases (INER). The patient responded well to antiviral treatment and is now recovered.
- Influenza A(H3N2) circulates annually in Mexico.
- Subclade K presents similar symptoms and behavior to other seasonal variants.
- Vaccination remains the primary prevention tool.
- The National Surveillance System (SINAVE) maintains continuous monitoring and will report any updates.
Symptoms: How does this variant manifest?
According to available evidence, the symptoms are the same as any seasonal influenza:
- Sudden fever
- Headache
- Muscle and joint pain
- Dry cough
- Nasal congestion or discharge
- Sore throat
- Extreme fatigue
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In high-risk individuals (older adults, pregnant women, those with chronic illnesses), influenza can progress to complications such as pneumonia or dehydration.
Does the vaccine work against subclade K?
Although data from this season are still being gathered, preliminary analyses in Europe show that the vaccine maintains similar levels of protection against severe illness compared to previous years:
- 70-75% effectiveness in girls and boys
- 30-40% effectiveness in adults
This level of efficacy helps reduce hospitalizations and complications, especially in high-risk groups.
What does PAHO recommend?
- Strengthen epidemiological, virological, and genomic surveillance.
- Ensure high vaccination coverage, particularly in older adults and individuals with comorbidities.
- Prepare health services for possible early or more intense influenza activity during winter.
- Treat cases promptly and ensure antiviral availability.
- Maintain early diagnosis and immediate notification of unusual respiratory events.
What precautions should the population take?
- Frequent handwashing.
- Covering the arm when coughing or sneezing.
- Ventilating enclosed spaces.
- Getting vaccinated against influenza, COVID-19, and pneumococcus according to age and health condition.
- If experiencing fever or respiratory symptoms, stay home and avoid contact with others.
- If testing positive for influenza, seek early attention and receive antiviral treatment if necessary.
