What to know about the influenza flu shot

The vaccine exposes the immune system to a safe signal from selected influenza strains, allowing it to build a response before exposure to the virus. Protection is not immediate and influenza viruses change, so seasonal vaccination is used. The shot cannot cause influenza infection. It also does not prevent every cough or fever caused by other viruses. Read about [Influenza](/conditions/influenza/) and symptoms such as [Fever](/symptoms/fever/).

Tell the vaccinator about previous vaccine reactions, severe allergies, pregnancy, immune conditions, and medicines you take. Mention if you are currently unwell. After the injection, a sore arm, mild fever, [Headache](/symptoms/headache/), or tiredness can occur and usually settles without treatment. Keep the area clean, rest if needed, and follow the clinic's aftercare advice.

Seek urgent help for swelling of the face or throat, widespread hives, wheezing, faintness, or trouble breathing after vaccination. Contact a clinician for symptoms that are severe, unexpected, or not settling. A vaccine does not treat an influenza illness that has already started; seek advice for worsening [Cough](/symptoms/cough/) or breathing problems, which can occur with [Pneumonia](/conditions/pneumonia/).

Ask which vaccine is appropriate, when to receive it, whether your health conditions affect the decision, and how to manage a previous reaction.