GASTRO INTESTINAL BLEED; HYPOXEMIC; CONFIRMED COVID-19 INFECTION; CONFIRMED CLINICAL VACCINATION FAILURE; This spontaneous report was received from literature. This report concerned an 84 year old male of of unknown race and ethnicity. The patient's height, and weight were not reported. The patient's concurrent conditions included: end stage kidney disease (ESKD) and hemodialysis. The patient had a prior response to the Hepatitis B vaccine with a recent titer greater than 10 IU/L. SARS-CoV-19 Antibody (AB) (IgG AB to the spike protein) was being checked monthly as part of an observational cohort. SARS-CoV-19 AB was negative 1 month prior to receiving a viral vector-based vaccine. The patient received covid-19 vaccine ad26.cov2.s (suspension for injection, route of admin, and batch number: Unknown and expiry: Unknown) 1 total dose, start therapy date were not reported for prophylactic vaccination. The batch number was not reported and has been requested. No concomitant medications were reported.  The Antibody (AB) was rechecked 1 month after the vaccine and remained negative. He was soon after admitted for Gastrointestinal (GI) bleed and tested positive for COVID-19 (confirmed covid-19 infection) by PCR nasal swab (confirmed clinical vaccination failure) on routine hospital screening. Hospitalization days were not specified. On discharge, he was asymptomatic but was hypoxemic requiring oxygen. 17 days after hospital discharge, SARS-CoV-19 by nasal PCR remained positive and AB titer was detectable at 1.3 U/L. Both were checked again 1 week later, viral PCR remained negative with further increase in AB to 2.3 U/L. A titer of greater than 2.0 U/L had been reported as protective. He was no longer hypoxemic by that time. The author emphasize that there was evidence in the general public that efficacy of the viral vector based SARS-CoV-19 vaccine might be lower than that of mRNA vaccines. With ESKD patients more susceptible to infection and less able to mount AB's to vaccines, this case supports the use of mRNA SARS-CoV-19 vaccines preferentially in the ESKD population if AB seroconversion was the targeted intermediary outcome. The action taken with covid-19 vaccine ad26.cov2.s was not applicable. The patient recovered from hypoxemic, and confirmed covid-19 infection, and the outcome of confirmed clinical vaccination failure and gastro intestinal bleed was not reported. This report was serious (Hospitalization Caused / Prolonged). This report was associated with product quality complaint.; Sender's Comments: V0: 20211128418-covid-19 vaccine ad26.cov2.s-Gastro intestinal bleed, confirmed covid-19 infection, hypoxemic. This event(s) is considered unassessable. The event(s) has a 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). 20211128418-covid-19 vaccine ad26.cov2.s-confirmed clinical vaccination failure. This event(s) is considered not related. The event(s) 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(s) than the drug. Specifically: SPECIAL SITUATIONS