H3N2 influenza: what to know

H3N2 is one of the influenza A virus subtypes. Infection may begin abruptly with fever, chills, headache, cough, marked tiredness, and a generally unwell feeling. Muscle aches and sore throat can also occur. Symptoms overlap with other respiratory infections, so a label based on symptoms alone is not certain. Influenza can sometimes affect the lungs and lead to pneumonia, particularly when breathing symptoms worsen or recovery does not follow the expected pattern.

Rest, drink fluids regularly, and use suitable fever or pain relief according to the label or professional advice. Stay home while acutely unwell and reduce close contact with others; cover coughs and wash hands. Contact a clinician early if you are pregnant, older, immunocompromised, or have a long-term condition, because antiviral treatment may be considered and timing can matter. Do not use antibiotics unless prescribed for a bacterial infection.

Seek emergency care for difficult breathing, blue or grey lips, severe chest pain, confusion, collapse, or inability to keep fluids down. Get prompt advice for fever or cough that improves and then returns, worsening weakness, dehydration, or symptoms that are becoming more severe. Children, older adults, and people with chronic illnesses may need assessment sooner.

Ask whether testing is useful, whether antiviral treatment fits your situation, and how to manage your existing medicines. Discuss how to protect household members and which changes in cough, fever, or breathing should trigger another review.