REVACCINATION WITH DIFFERENT COVID-19 VACCINE; CONFIRMED CLINICAL VACCINATION FAILURE; CONFIRMED COVID-19 INFECTION (REBOUND); This spontaneous report received from a patient via other manufacturer (Pfizer) concerned a patient of unspecified age, sex, race, and ethnicity. Initial information was processed along with the additional information received on 19-OCT-2023. The patient's height, and weight were not reported. The patient's concurrent conditions included: familial hyperlipidemia, hypertension, and allergy. The patient received covid-19 vaccine ad26.cov2.s (dose number in series 1) (suspension for injection, route of admin, batch number and expiry date were not reported) dose was not reported, 1 total (first dose) administered on 17-MAR-2021 for covid-19 prophylaxis. The batch number was not reported. The Company is unable to perform follow-up to request batch/lot numbers. Concomitant medications included atenolol, clonazepam, evolocumab, and zolpidem. The patient received three doses of Non-company suspect vaccine included: Pfizer (tozinameran) (dose number in series 2) (form of admin, route of admin, batch number and expiry date were not reported) dose was not reported, second dose was administered on 18-JAN-2022, third dose on 27-MAY-2022 and fourth dose on JUL-2022 for covid-19 prophylaxis. It was unknown whether patient had any adverse events following vaccination with three doses of tozinameran (dose number in series 2). The patient received another two doses of Non-company suspect vaccine included: Pfizer (tozinameran) (dose number in series 3) (form of admin, route of admin, batch number and expiry date were not reported) dose was not reported, fifth dose was administered on 25-SEP-2022 and sixth dose on JUN-2023 for covid-19 prophylaxis. It was unknown whether patient had any adverse events following vaccination with two doses of tozinameran (dose number in series 3).. The patient additionally received Non-company suspect vaccine included: Pfizer (tozinameran) (dose number in series 4) (form of admin, route of admin, batch number and expiry date were not reported) dose was not reported, seventh dose was administered on 26-SEP-2023 at left arm for covid-19 prophylaxis which was revaccination with different covid-19 vaccine (dose number in series 4). On 2023, the patient experienced confirmed covid-19 infection (dose number in series 4) which leads to confirmed clinical vaccination failure (dose number in series 1). The patient was treated with Paxlovid (nirmatrelvir/ritonavir) (form of admin, route of admin were not reported, batch number: unknown and expiry: unknown) dose was not reported, administered from 02-OCT-2023 to 06-OCT-2023 for treatment of covid-19 (confirmed covid-19 infection). On 15-OCT-2023, the patient experienced confirmed covid-19 infection (rebound) (dose number in series 4). On OCT-2023, Laboratory data included: SARS-CoV-2 test Positive. On 15-OCT-2023, the patient still tested positive for SARS-CoV-2 test after a complete cycle of Paxlovid. The action taken with covid-19 vaccine ad26.cov2.s, tozinameran (dose number in series 2), tozinameran (dose number in series 3), and tozinameran (dose number in series 4) was not applicable. The patient had not recovered from confirmed covid-19 infection (rebound), and the outcome of confirmed clinical vaccine failure and revaccination with different covid-19 vaccine was not reported. This report was serious (Other Medically Important Condition). This report was associated with product quality complaint: 90000300839.; Sender's Comments: V0: 20231046449- confirmed clinical vaccination failure . The event has a compatible/suggestive temporal relationship, is unlabeled, and has unknown scientific plausibility. There are other factors more likely to be associated with the event. Specifically: SPECIAL SITUATIONS. Therefore, this event is considered inconsistent with vaccine administration.