What to know about the influenza vaccine

Influenza vaccines expose the immune system to selected viral components so it can prepare a response before a future encounter. The injected vaccine is commonly inactivated, meaning it does not contain live virus capable of causing influenza. Protection is not immediate, and influenza viruses change over time, which is why vaccination may be offered again for a new flu season.

Vaccination can still be useful even though it cannot prevent every respiratory infection. Colds and other viruses can produce flu-like symptoms, and a person may encounter influenza before immunity has developed. If influenza occurs after vaccination, prior immune preparation may reduce the severity of illness.

Tell the vaccinator about a current fever, previous serious vaccine reaction, allergies, immune-system treatment, pregnancy, bleeding problems, and any medicines you take. A mild illness without fever does not always require postponement, but the vaccinator should assess your situation. Wear clothing that gives easy access to the upper arm and remain for the observation period advised by the clinic.

A sore arm, tiredness, headache, or mild fever can occur as the immune response develops. Rest, drink fluids, and move the arm gently. Ask a clinician or pharmacist which pain or fever medicine is suitable for you if needed. Keep the vaccination details with your health records, especially if you receive care from several providers.

Get emergency help for difficulty breathing, swelling of the lips, tongue, face, or throat, widespread hives, collapse, severe dizziness, or rapidly worsening symptoms after vaccination. These can signal a serious allergic reaction and should not be managed at home.

Seek medical advice if fever is high or persistent, a reaction is getting worse rather than easing, or you develop weakness, numbness, or other concerning neurological symptoms. Symptoms such as chest pain, severe shortness of breath, confusion, blue or grey lips, or inability to stay awake require urgent assessment whether or not they follow vaccination.

Ask which vaccine formulation is suitable for your age and health conditions, whether today's symptoms affect timing, and how a previous reaction changes the plan. If you are pregnant, immunocompromised, taking anticoagulants, or receiving other vaccines, clarify the recommended product, injection method, and timing with the vaccinator.