4 days later she had a blood test that showed that her platelets were low with "alert"; she got the third Pfizer shot; she got the third Pfizer shot; This is a spontaneous report from a contactable consumer (patient). A 75-year-old female patient BNT162B2 (PFIZER-BIONTECH COVID-19 VACCINE, Solution for injection, Batch/Lot Number: SC3180, Expiry Date, UPC, NDC number: Unknown), dose 3 via an unspecified route of administration on 16Aug2021 (at the age of 75-years-old) as DOSE 3 (Booster), SINGLE for covid-19 immunisation. Medical history included ongoing rheumatoid arthritis; ongoing Linear Scleroderma, she was diagnosed in her twenties; ongoing scleroderma; ongoing heart disease, she had two stents placed a while ago. Stated that the last stent was maybe 10 years ago, this was prior to the Pfizer Covid shot.; all were from an unknown date. Concomitant medications were not reported. The patient takes medicines for heart disease, rheumatoid arthritis and other vitamins. There was nothing to do with the medication. Historical vaccine includes first dose of BNT162B2 (lot number of EN6204 and expiration date of 30Jun2021) on 12Mar2021 in the unknown arm and second dose of BNT162B2 (lot number of EN0150 or EW0150) on 02Apr2021 in the unknown arm; Does not have NDC numbers to provide for either shot; both doses for COVID-19 immunisation. The patient received her third vaccine dose on 16Aug2021, she got the third Pfizer shot because the patient was immunocompromised, her doctor stated that she had rheumatoid arthritis and scleroderma with an immune system that was compromised and 4 days later (20Aug2021), patient had a blood test that showed that her platelets were low with "alert" next to it. Patient got hospitalized for reported event. The patient was asking if low platelets are a side effect of the vaccine and if so, will the platelets rebound once her immunity was boosted. The patient spoke with her doctor, told him that she recently got the shot and asked if there was a correlation, they didn't know, but she reports that her doctor was planning to repeat the lab work tomorrow and again in 3month time. Reports that her follow up is already scheduled. The patient wanted to know if there is a possibility that there was a correlation between low platelets and getting the vaccine and if her platelets would rebound after her body makes antibodies for vaccine. Stated that it was for the Pfizer Covid shot. Stated that they took another blood test today and won't know the results for a few days. Stated that she had no other blood tests since August. This was the third one that's correct. The patient had completed in 02Apr2021, patient got second shot and so patient was completely covered by the mid of April, two weeks after. And when they came out with possible whining of the antibiotics. When they came to that specially in people that were immunocompromised it's suggested that patient immediately get a shot. So, patient went over on the day and got a shot. The patient husband and patient got the third shot. And 3 or 4 days later I got blood test for my rheumatologist and she called me yesterday and said, listen your blood work was paused and that's do not usual for you and she asked are you bleeding and she said to me I don't want you to get scared it's not so low that you have to go to hospital or be transfused but its low and its concerning and that's when patient said to her, patient just got the Pfizer shot in fact patient said to my doctor. According to reporter Pfizer product had a causal effect to the adverse event The patient underwent lab tests and procedures which included platelet count: low on 20Aug2021 and blood test: unknown results on 25Aug2021 blood test today and won't know the results for a few days. Outcome of the events was unknown.  Follow-up attempts are completed. No further information is expected.  Follow-up (28Sep2021): This is a follow-up spontaneous report from a contactable Physician. This Physician reported in response to HCP letter sent via follow up letter activity which included new information that: Patient Provide information regarding reported adverse event 1x by Hospitalized decrease platelet. Pfizer product had a causal effect to the adverse event.  Follow-up attempts completed. No further information expected.; Sender's Comments: As there is limited information in the case provided, the causal association between the events Platelet count decreased, Off label use, Extra dose administered and the suspect BNT162B2 cannot be excluded.  The impact of this report on the benefit-risk profile of the Pfizer product and on the conduct of the study is evaluated as part of Pfizer procedures for safety evaluation, including the review and analysis of aggregate data for adverse events. Any safety concern identified as part of this review, as well as any appropriate action in response, will be promptly notified to regulatory authorities, ethics committees, and investigators, as appropriate.