diagnosed with Mono/mononucleosis; Epstein-Barr virus; sick; This is a spontaneous report from a contactable Nurse (mother of patient) reported her son. A 17-year-old male patient received bnt162b2 (PFIZER-BIONTECH COVID-19 VACCINE, formulation: Solution for injection, Lot number was not reported and Expiration date: unknown), dose 1 via an unspecified route of administration, administered in Deltoid Left on 11Aug2021 at 11:00 (not 100 percent sure about time) (at the age of 17-year-old) as DOSE 1, SINGLE for covid-19 immunisation. There were no additional Vaccines Administered on Same Date of the Pfizer Suspect. Medical history was none. There were no concomitant medications. Patient medical history (including any illness at time of vaccination) was none. The patient had no family medical history relevant to AE. No other vaccinations within four weeks prior to the first administration date of the suspect vaccine. No AE(s) following prior vaccinations. On 24Aug2021, the patient diagnosed with mononucleosis, Epstein-Barr virus and had been sick for like a week. The clinical details of the events as follows: Caller was calling about her son who is 17 years old. The caller is a NP. The patient received his first dose of the Pfizer COVID-19 Vaccine on 11Aug2021. Patient now had been diagnosed with Mono. Because of this new diagnosis, the caller was now hesitant to get him the second dose of his vaccine that he is supposed to receive on 02Sep2021. Caller requested to speak to a scientist or doctor with Pfizer regarding her situation and other cases possibly. The caller understanded that there was minimal information available on teens, but she would like to get further guidance on what the recommendation would be for her son having had the 1st dose and now having Mono. She did not mention speaking to a higher level than a RN several times with the backing that she is not trying to undermine. She would like to know if this was something Pfizer has knowledge about. She stated that this was above her medical knowledge as a practicing Nurse Practitioner as well. She stated that her situation was unique, and she understands this. Caller also stated that her HCP, nobody knows anything about anything to be honest. Caller stated obviously as a medical provider myself, I am not giving him the 2nd vaccine. I am not messing with his immune system while he is fighting mono. The patient went to the physician office due to the events. The caller son now has mononucleosis, Epstein-Barr Virus. The caller was asking for guidance on the son receiving the second dose Pfizer Covid Vaccine. The caller stated she knows there was no data on someone with mononucleosis and the Pfizer Covid Vaccine. The caller son now has mononucleosis within 3 weeks of receiving the Pfizer Covid Vaccine and the patient was due for his second dose Pfizer Covid Vaccine. The caller did not think the patient should receive the second dose Pfizer Covid Vaccine, knows the Pfizer Covid Vaccine effects the immune system. The caller was not happy about the situation. The caller is a Nurse Practitioner and was on the fence about her son receiving the Pfizer Covid Vaccine, but the caller did the right thing for her son. The caller wanted to speak to someone about guidance on the second dose Pfizer Covid Vaccine. The caller did think the son was going to receive the second dose Pfizer Covid Vaccine. Relevant Tests were none. Now has mononucleosis, Epstein-Barr Virus, the caller stated she knew this was not a side effect. She stated mononucleosis and Epstein-Barr virus were Unrelated to Pfizer Covid Vaccine. There was no Investigation Assessment provided. The patient outcome of the events was unknown at the time of this report. Causality: The caller stated this was not a side effect of the Pfizer Covid Vaccine.   The lot number for the vaccine, [BNT162B2], was not provided and will be requested during follow up.