Brief Answer: Possible allergy reaction to flu shot Detailed Answer: Hi XXXXXXX, Thanks for writing in to us. I have read through your query in detail. You have said that a pea sized swelling has suddenly appeared above your collar bone (supraclavicular region). The commonest swelling above the collar bone region is a lymph node that may have enlarged. There are many reasons for lymph node enlargement including suspected allergy reactions(as you have reported), acute and chronic infections and rarely malignancies. Possibility of an insect bite swelling may also be there which can cause a small swelling under the skin, but that is usually little painful. The most likely cause of your swelling may be an allergic reaction to the flu shot. The vaccines contain small amounts of chemical which can potentially trigger a reaction swelling in the lymph nodes. I would suggest you to consult a surgeon and also take note of swellings anywhere else in your body and discuss the same with your doctor. After clinical examination, you might be put on medications which may include anti allergy ones and anti inflammatories. If it confirms an presence of an infection an antibiotic can be given. It the swelling does not resolve in a few days, your doctor might suggest an ultrasound scan and further investigations if felt necessary. Hope your query is answered. Do write back in case of doubts. Regards, Dr.Vivek

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