This is a spontaneous report from a contactable consumer (patient). A 56-year-old female patient received the second dose of BNT162B2 (PFIZER-BIONTECH COVID-19 VACCINE), via an unspecified route of administration on 31Mar2021 at 13:15 (Lot/batch number: ER8733, Expiration date: 31Jul2021) on the left arm as single dose for COVID-19 immunization. Medical history included osteoarthritis. Concomitant medications included ongoing methotrexate sodium, ongoing sulfasalazine and unspecified drug. The patient previously took the first dose of BNT162B2 (PFIZER-BIONTECH COVID-19 VACCINE), via an unspecified route of administration on 10Mar2021 at 15:00 as single dose for COVID-19 immunization. No additional vaccines administered on same date with the Pfizer vaccine considered as suspect. No prior vaccinations (within 4 weeks), no events following prior vaccinations. Patient received the second dose of the Pfizer COVID-19 vaccine on 31Mar2021. She received a phone call yesterday (13Apr2021) from the vaccination site that an error was made and a small group of patients possibly received saline instead of the vaccine. Patient stated she was "99.99% sure I got the vaccine" because she had the following side effects: headache that night and couldn't sleep. The next day she had body aches, a little fever of 100, and a sore arm. The vaccination site was recommending per the CDC to revaccinate everyone who potentially received saline any time after 21Apr2021. Patient was currently scheduled to receive a revaccination with a third dose on 23Apr2021. She wanted to know if she should take a third dose, she knew there were studies about taking a third dose as a booster. Patient was thinking about canceling the revaccination as there wasn't enough information on the study regarding a third vaccine. Patient thought she did receive the COVID-19 vaccine because she had a headache and sore arm on 31Mar2021. The night she received the COVID-19 vaccine she was restless and could not sleep. She had body aches and a fever and was really achy the next day. She's thinking she received the COVID-19 vaccine and not just saline. She explained her situation to a nurse and a pharmacist, and she was told that saline could cause a fever. She's been advised to receive a third COVID-19 vaccine 21 days after the date of the second COVID-19 vaccine. Patient reported due to the COVID-19 virus she had gained weight. On 31Mar2021 she could not sleep at all. It was like she was on steroids. She got up at 3:00AM to read. She had a little injection site pain the day of the vaccine but that was gone the next day. She had a fever of 100 degrees Fahrenheit on 01Apr2021. Then half an hour later her temperature would be normal, then a couple hours later she'd have a fever again. She knew she had a fever because she felt hot. On Saturday, 03Apr2021 she woke up and did her normal Saturday things. She felt better and her symptoms had resolved. Lab data included patient temperature was 100 degrees Fahrenheit on 01Apr2021. No events required a visit to emergency room or physician office. The outcome of the event possibly received saline instead of the vaccine was unknown, the events sore arm and injection site pain was recovered on 01Apr2021, while of the other events was recovered on 03Apr2021. No follow-up attempts are needed. No further information is expected.