INFLAMMATORY POLYARTHRITIS; This spontaneous report received from a consumer concerned a 41 year old male. The patient's height, and weight were not reported. The patient's pre-existing medical conditions included: Patient was healthy and physically active individual with no notable medical history prior to receiving the vaccine. The patient received covid-19 vaccine ad26.cov2.s (Dose number in series 1) (suspension for injection, route of admin not reported, batch number: 1855194, expiry: unknown) dose was not reported, 1 in total administered on 11-NOV-2021 for covid-19 prophylaxis.  On an unspecified date in 2021 (several days after receiving the vaccine), patient experienced pain in his right leg joints and had to leave work (Dose number in series 1). On 27-DEC-2021, the patient was seen at urgent care and was prescribed Naproxen (Naprosyn). The outcome of the pain in his right leg joints was not reported. The patient received covid-19 vaccine ad26.cov2.s (Dose number in series 2) (suspension for injection, route of admin not reported, batch number: 211D217, expiry: unknown) dose was not reported, 1 in total administered on 29-JAN-2022 for covid-19 prophylaxis. Age at time of vaccination 41 years old. No concomitant medications were reported.  On an unspecified date in 2022 (after receiving the vaccine), patient traveled outside of the country and while away, patient experienced increased pain on his right leg joints and had to return (Dose number in series 2). It was reported that, the pain eventually spread to his left leg joints and then to other parts of the body (Dose number in series 2). Patient visited his primary care physician (physician office visit) several times. Patient's joints became swollen and he experienced difficulties walking (Dose number in series 2). On 25-JUN-2022, the patient went to the emergency room. Patient was prescribed oxycodone hydrochloride/paracetamol (Percocet) and released. Patient's condition was severely deteriorated. He experienced severe pain on multiple joints and could barely walk at that point (Dose number in series 2). On 12-JUL-2022, patient was transported by ambulance to the hospital and the patient remained hospitalized until 27-JUL-2022 for 15 days, when the patient was released to rehabilitation center. While at the hospital, several tests were conducted on the patient. Patient was diagnosed with inflammatory polyarthritis and was prescribed several medications which included: famotidine (Pepcid), rifampicin (Rifadin), prednisolone (Deltasone), cyclobenzaprine hydrochloride (Flexeril), sennoside a plus b (Senokot), ferrous sulfate (Iron), macrogol 3350 (Miralax), and oxycodone hydrochloride/paracetamol (Percocet). Patient stayed at rehabilitation center after his release from hospital until 20-AUG-2022. While at rehabilitation center patient was followed by a physician, and was regularly visited by nurses, and currently follows several drug regimens. At the time of reporting, patient was still experiencing pain on several joints with intermittent joint swelling (Dose number in series 2).  The action taken with covid-19 vaccine ad26.cov2.s was not applicable. The patient had not recovered from inflammatory polyarthritis.  This report was serious (Hospitalization Caused / Prolonged). This case, involving the same patient is linked to 20220936991 (Dose number in series 1).; Sender's Comments: V0:20220938918-covid-19 vaccine ad26.cov2.s -inflammatory polyarthritis. The event(s) has an compatible/suggestive temporal relationship, is unlabeled, and has unknown scientific plausibility. There is no information on any other factors potentially associated with the event(s). Therefore, this event(s) is considered unassessable