Rheumatoid arthritis; Patient is immunocompromised received 1st booster dose of the Moderna Covid-19 vaccine; Patient is immunocompromised received 1st booster dose of the Moderna Covid-19 vaccine; This spontaneous case was reported by a pharmacist and describes the occurrence of RHEUMATOID ARTHRITIS (Rheumatoid arthritis) in a 77-year-old male patient who received mRNA-1273 (Moderna COVID-19 Vaccine) for COVID-19 vaccination. The occurrence of additional non-serious events is detailed below.     Concurrent medical conditions included Atrial fibrillation and Immunocompromised.   On 08-Jan-2021, the patient received first dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) 1 dosage form. On 05-Feb-2021, received second dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) dosage was changed to 1 dosage form. On 19-Nov-2021, received third dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) dosage was changed to .25 milliliter. In November 2021, the patient experienced RHEUMATOID ARTHRITIS (Rheumatoid arthritis) (seriousness criterion medically significant), ACCIDENTAL UNDERDOSE (Patient is immunocompromised received 1st booster dose of the Moderna Covid-19 vaccine) and INAPPROPRIATE SCHEDULE OF PRODUCT ADMINISTRATION (Patient is immunocompromised received 1st booster dose of the Moderna Covid-19 vaccine). At the time of the report, RHEUMATOID ARTHRITIS (Rheumatoid arthritis), ACCIDENTAL UNDERDOSE (Patient is immunocompromised received 1st booster dose of the Moderna Covid-19 vaccine) and INAPPROPRIATE SCHEDULE OF PRODUCT ADMINISTRATION (Patient is immunocompromised received 1st booster dose of the Moderna Covid-19 vaccine) outcome was unknown.        For mRNA-1273 (Moderna COVID-19 Vaccine) (Unknown), the reporter did not provide any causality assessments.   Concomitant information was not provided. The patient has received the 1st, 2nd doses and the 1st booster dose of the Moderna Covid-19 vaccine. He was diagnosed to have rheumatoid arthritis after his 1st booster dose (Nov2021) and was on anti suppressive medication. patient now at the pharmacy for his 2nd booster dose but patient was told by his doctor that patient is immunocompromised. COMPANY COMMENT: This is an spontaneous case concerning a 77-years-old male patient with medical history of Concurrent medical conditions included Atrial fibrillation and Immunocompromised, Moderna COVID-19 Vaccine on 1/8, 2/5 and 11/19 of 2021 who experienced the unexpected events of RHEUMATOID ARTHRITIS (AESI, seriousness criterion medically significant), ACCIDENTAL UNDERDOSE and INAPPROPRIATE SCHEDULE OF PRODUCT ADMINISTRATION unknown days after 3rd  dose of  mRNA-1273 vaccine. The benefit-risk relationship of mRNA-1273 vaccine is not affected by this report. Event´s seriousness assessed as reporting.; Sender's Comments: COMPANY COMMENT: This is an spontaneous case concerning a 77-years-old male patient with medical history of Concurrent medical conditions included Atrial fibrillation and Immunocompromised, Moderna COVID-19 Vaccine on 1/8, 2/5 and 11/19 of 2021 who experienced the unexpected events of RHEUMATOID ARTHRITIS (AESI, seriousness criterion medically significant), ACCIDENTAL UNDERDOSE and INAPPROPRIATE SCHEDULE OF PRODUCT ADMINISTRATION unknown days after 3rd  dose of  mRNA-1273 vaccine. The benefit-risk relationship of mRNA-1273 vaccine is not affected by this report. Event´s seriousness assessed as reporting.