received first dose of Moderna Covid-19 vaccine, but when he went back to receive his second dose, he received the Pfizer Covid-19 vaccine; received first dose of Moderna Covid-19 vaccine, but when he went back to receive his second dose, he received the Pfizer Covid-19 vaccine; he started getting headaches; soreness; This is a spontaneous report from a Pfizer sponsored program. A contactable Consumer (patient's grandmother) reported for a 27-year-old Male patient (reporter's Grandson). A 27-years-old male patient received bnt162b2 (PFIZER-BIONTECH COVID-19 mRNA VACCINE, Formulation: Solution for injection, Batch/Lot number was not reported), dose 2 via an unspecified route of administration on an unspecified date as dose 2, single (initial Pfizer dose, single) for covid-19 immunisation. The patient's medical history and concomitant medications were not reported. Family medical history included chronic obstructive pulmonary disease from an unknown date and unknown if ongoing patient's grandmother have COPD. Historical vaccine given to patient previously was Moderna Covid-19 vaccine, dose 1 via an unspecified route of administration on an unspecified date as dose 1, single for COVID-19 immunisation. It was reported that caller was a consumer inquiring about additional information for the Pfizer Covid-19 vaccine. Caller reported that her grandson (27 years old, male) received first dose of Moderna Covid-19 vaccine, but when he went back to receive his second dose, he received the Pfizer Covid-19 vaccine. She reported that he was told to get second dose of Pfizer vaccine and caller asked was this correct, does he need a second shot. Caller stated, "I am not sure how that happened, it was given at the same office". The question was now, the nurse wrote on his vaccination and said in 3 weeks to come back for his second dose of Pfizer, but the doctor said he does not need to get it. "I did not think there is anyone that knows. I would think Pfizer would know, but I know it was not helping to call Moderna. I know there is not a lot of data, I am sure he is not the first one that this happened to". Doctor said he does not need second Pfizer shot. He lives with me, and reporter have COPD and his little girl comes every 2 weeks, were making sure he was completely vaccinated to protect reporter and patient's daughter. He was perfectly healthy. Everyone refers back to HCP, but he was the one who gave wrong shot. If they did not have Moderna they should have said that he tried to get in to see his doctor because he started getting headaches and soreness but cannot be seen until Friday. He thought about going to one of the emergency rooms to make sure his lymph nodes are not swollen and not running a fever. Were just trying to be overly cautious. "I am perplexed. If something weird is going to happen it will happen to someone in my house. If I could just get in touch with (Withheld) he could give me a good recommendation. Nowhere can you find information about Moderna and Pfizer and just not knowing whether he should go back for the second shot". Swap from FC Caller's grandson had received the 1st dose of the Moderna vaccine but for the 2nd dose was given the Pfizer vaccine and is now being told to take a 2nd dose of the Pfizer vaccine. Caller would like to know if this is the correct way to proceed. No product quality complaint was reported. The outcome of the event was reported as unknown.  The lot number for the vaccine, [BNT162B2], was not provided and will be requested during follow up.