Understanding the influenza flu vaccine

Vaccination gives the immune system information it can use to respond more quickly if it encounters influenza. The formulation is updated as circulating strains change, and immunity develops after vaccination rather than at the moment of injection. The vaccine is designed for influenza; it will not prevent every respiratory infection. For context, see [Influenza](/conditions/influenza/) and [Feeling Generally Unwell](/symptoms/feeling-generally-unwell/).

Share your allergy history, past vaccine reactions, pregnancy status, immune conditions, and current medicines with the vaccinator. Ask about timing if you have an acute illness. Mild soreness at the injection site, tiredness, [Headache](/symptoms/headache/), or a low fever may follow. Rest, drink fluids, and use symptom relief only as directed. Report anything that concerns you rather than assuming it is expected.

Call for urgent medical help if you develop facial or throat swelling, hives with breathing difficulty, wheezing, or faintness soon after vaccination. Seek clinical advice for a severe or persistent reaction. If you already have influenza, vaccination will not cure it; worsening [Cough](/symptoms/cough/) or shortness of breath needs assessment, including consideration of [Pneumonia](/conditions/pneumonia/).

Ask which vaccine is suitable for your age and health, when protection is expected to develop, and what to do if you have reacted to a vaccine before.