Lymph node pain in breast tissue of a nursing mom (located near arm pit on the side opposite of injection site (injection left arm, right breast lymph node pain). Pain is NOT severe but noticeable; Swollen lymph node; Breast pain in the armpit and adjacent breast tissue; Off label use; Drug use in unapproved population; This is a spontaneous report received from a contactable reporter(s) (Consumer or other non HCP). The reporter is the patient.  A 37 year-old female patient (not pregnant) received bnt162b2 (BNT162B2), administered in arm left, administration date 2021 (Batch/Lot number: unknown) at the age of 37 years as dose number unknown, single for covid-19 immunisation. Relevant medical history included: "Breast feeding" (ongoing), notes: Lactating mother. There were no concomitant medications.  The following information was reported: OFF LABEL USE (non-serious) with onset 2021, outcome "unknown", described as "Off label use"; PRODUCT USE ISSUE (non-serious) with onset 2021, outcome "unknown", described as "Drug use in unapproved population"; LYMPH NODE PAIN (non-serious) with onset 19Apr2021, outcome "recovering", described as "Lymph node pain in breast tissue of a nursing mom (located near arm pit on the side opposite of injection site (injection left arm, right breast lymph node pain). Pain is NOT severe but noticeable"; LYMPHADENOPATHY (non-serious) with onset 19Apr2021, outcome "recovering", described as "Swollen lymph node"; BREAST PAIN (non-serious) with onset 19Apr2021, outcome "recovering", described as "Breast pain in the armpit and adjacent breast tissue". The events "lymph node pain in breast tissue of a nursing mom (located near arm pit on the side opposite of injection site (injection left arm, right breast lymph node pain). pain is not severe but noticeable", "swollen lymph node" and "breast pain in the armpit and adjacent breast tissue" were evaluated at the physician office visit. Therapeutic measures were not taken as a result of lymph node pain, lymphadenopathy, breast pain.  Additional Information: The patient did not receive any other medicines within two weeks prior to the COVID-19 vaccine. The patient had no known allergies to medications, food or other products. Prior to the vaccination, the patient was not diagnosed with COVID-19. The patient did not receive any other vaccines within four weeks prior to the vaccination. On 19Apr2021, a nursing mom had lymph node pain in breast tissue of (located near arm pit on the side opposite of injection site (injection left arm, right breast lymph node pain). Pain was not severe but noticeable. It was reported that breast pain in a nursing mom could also be, and usually is in the patient's experience, a sign of mastitis (breast infection common to lactating mothers). As a result, the patient was more alarmed by the pain than she would have been if she was not nursing, and while the pain did not affect her daily life in any way. The patient thought it was important to mention swollen lymph nodes and breast pain in the armpit and adjacent breast tissue of a nursing mother so as to save other mothers the worry when they got vaccinated that the pain, they were feeling is something more sinister and possible temporary lymph node swelling. Since the vaccination, the patient had not been tested for COVID-19.   No follow-up attempts are possible; information about lot/batch number cannot be obtained. No further information is expected.; Sender's Comments: Linked Report(s) : US-PFIZER INC-202101137255 same reporter/drug, different event/patint(child)