Dr. Yong Warns of Severe Outbreak of Influenza A H3N2 Mutating to Evade Vaccines: How to Recognize Symptoms Differing from the Common Cold

Check the symptoms of influenza A H3N2 after Dr. Yong warned of a severe outbreak caused by the virus mutating to better evade vaccines, along with prevention methods and proper vaccination guidelines.

Professor Dr. Yong Poovorawan warned about the influenza situation in early 2026, noting that the A H3N2 strain has surged to a record high. He revealed that mutations in the virus's proteins allow it to better evade immunity, reducing vaccine effectiveness. He urged the public to watch for symptoms more severe than typical colds and offered guidance to reduce the risk of complications.

How do symptoms of “influenza A H3N2” differ from those of the common cold?

The first thing the public should know is the symptom differences to ensure timely treatment. Influenza A H3N2 usually causes more severe and sudden symptoms than the common cold, as follows.

Symptoms of influenza A H3N2

• Sudden high fever (38.5-40°C)
• Severe muscle aches and extreme fatigue
• Severe dry cough, sore throat, occasional runny nose
• Lasts 7-10 days or longer
• Risk of pneumonia, especially in vulnerable groups

Symptoms of the common cold

• Low fever or no fever
• Mild muscle aches that improve with rest
• Nasal congestion, runny nose, mild cough
• Resolves on its own within 3-5 days
• Rare complications

Explaining why influenza A H3N2 is spreading widely now

Professor Dr. Yong Poovorawan, head of the Clinical Virology Specialty Center in the Department of Pediatrics at Chulalongkorn University Faculty of Medicine, stated that the main reason influenza A H3N2 is spreading widely in early 2026 is genetic changes in the HA1 protein of the virus at about 6-9 points, known as the “K type” group.

These changes enable the virus to better “evade” immunity from previously administered vaccines (vaccine mismatch). Combined with winter and transitional seasons, which favor viral spread, this has led to the outbreak. However, Dr. Yong confirmed that “the severity of the disease has not increased” and current antiviral drugs remain effective; the number of infections is simply higher than usual.

Global attention on “Subclade K,” the variant driving rapid influenza A H3N2 spread

Besides Dr. Yong’s information, recent reports from the World Health Organization (WHO) and the U.S. Centers for Disease Control and Prevention (CDC) (as of January 2026) agree that the influenza A H3N2 virus causing the current global outbreak is a subvariant called “Subclade K” (or J.2.4.1). Some countries have nicknamed it “Super Flu” because

• of its unusual outbreak characteristics: CDC reports that Subclade K has caused outbreaks that are “longer than usual” in the Southern Hemisphere and “start earlier than usual” in several Northern Hemisphere countries like the UK, Canada, and Japan, with this variant accounting for up to 90% of influenza cases.
• Definition of “Antigenic Drift”: International sources describe this as a significant “genetic drift,” not just minor mutations. It involves changes at key positions on the hemagglutinin protein that make it much harder for the immune system to recognize the virus.

Is the flu vaccine still necessary and how effective is it?

Despite reports that mutations have reduced vaccine effectiveness, Dr. Yong still recommends continuing influenza vaccinations for two main reasons:

• Reducing severity: Although it cannot prevent infection 100%, the vaccine reduces the chance of severe symptoms, hospitalization, and death significantly.
• High safety: The vaccines used are inactivated types, with few side effects and a strong safety profile.
• Advice for Thai people The new Southern Hemisphere vaccine formula will arrive around March 2026, which is the best time to get vaccinated to build immunity before the rainy season, Thailand’s major outbreak period.

Vaccine effectiveness varies by age group from a global perspective

While emphasizing vaccination, data from the UK Health Security Agency (UKHSA) and European studies show the 2025/2026 vaccine’s effectiveness against Subclade K as follows:

• In children and adolescents: The vaccine remains highly effective, about 70-75% at preventing hospitalization.
• In adults: Effectiveness may drop to about 30-40% due to immune evasion by the new variant.
• International recommendations Although adult effectiveness seems lower, WHO continues to recommend vaccination for high-risk groups—those 65 and older and people with chronic illnesses—as it is the only tool to build “cross-strain immunity” that best reduces severe pneumonia risk.

How to protect yourself from influenza A H3N2

Besides vaccination, personal hygiene is crucial to breaking the outbreak chain, including:

• Wearing a mask in public or crowded places
• Frequent handwashing with soap and water or alcohol gel, since the virus easily spreads via hands
• Avoid close contact with the sick; if a household member is ill, isolate their room and personal belongings
• Maintaining good health by resting adequately, eating nutritious food, and exercising regularly