Hi, thank you for asking Healthcare Magic. I have gone through your query and understood your concerns. Actually, a tetanus shot can lead to swollen lymph nodes under the armpit but it is important to rule out other causes. These include disorders affecting the breast (including cancers) and systemic disease. To rule out these conditions, you need to undergo a thorough clinical assessment and do some tests like mammography, breast ultrasound, MRI of breast and biopsy of lymph node. In my opinion, I think you should go back and complain about the lymph node. I hope I have answered your query. I wish you good health