CONFIRMED CLINICAL VACCINATION FAILURE; BREAKTHROUGH COVID-19 INFECTION AFTER VACCINATION; This spontaneous report was received from literature. Transplantation.  Initial information was processed along with additional information received on 04-MAY-2022. The objective of the article was to assess the baseline characteristics and IS regimen among a cohort of vaccinated LT (lung transplant) patients who developed breakthrough infections and contrast them to a control group of vaccinated LT patients without coronavirus disease 2019 (COVID-19). This report concerned an adult patient of an unspecified sex, race and ethnicity. The patient's height, and weight were not reported. The patient had lung transplant and was maintained on standard triple immunosuppressive regimen (prednisone, calcineurin inhibitor and antimetabolite) as per protocol at the time of vaccination. The patient received covid-19 vaccine ad26.cov2.s (suspension for injection, route of admin not reported, batch number: unknown) dose, start therapy date were not reported, 1 total administered for prophylactic vaccination. The batch number was not reported and has been requested. This cohort consisted of 14 patients who were fully vaccinated and had symptomatic breakthrough covid-19 infection. These patients tested positive for severe acute respiratory syndrome coronavirus 2 on a nasopharyngeal swab between 01-MAR-2020 and 24-SEP-2021. On an unspecified date, the patient experienced breakthrough covid-19 infection (covid-19) after vaccination where the median time from vaccination to breakthrough infection was 138 days (range, 42179 days) in the cohort and the patient was tested positive for sars-cov-2 on nasopharyngeal swab test which was coded as confirmed clinical vaccination failure. All patients in the cohort were maintained on standard triple immunosuppressive regimen as per protocol at the time of vaccination and was not modified for any of the patients around the time of vaccination. None of the patients had any change to their regimen between the time of vaccination and the breakthrough infection. One of the patient had received 1 dose of rituximab (375mg/mE2) 6week before the first vaccine dose and monthly intravenous immunoglobulin infusions. As per the study patients with breakthrough infection seemed more likely to be on MMF (mycophenolate mofetil) as the antimetabolite, and a higher proportion of patients with breakthrough infection were on daily MMF dose of more than 1000 mg. When compared with azathioprine or MMF dose of less than or equal to 1000 mg/d, the risk of breakthrough infection was significantly higher among patients on a daily MMF dose of more than 1000 mg. It was not reported which calcineurin inhibitor and antimetabolite drug was given to the patient. The action taken with covid-19 vaccine ad26.cov2.s was not applicable. The outcome of the breakthrough covid-19 infection after vaccination and confirmed clinical vaccination failure was not reported. The authors concluded that cohort of LT (lung transplant) patients with breakthrough covid-19 in whom high-dose MMF (mycophenolate mofetil) at the time of vaccination seemed to be independently associated with an increased risk of breakthrough infections. This report was serious (Other Medically Important Condition). This report was associated with a product quality complaint number: 90000229391.; Sender's Comments: V0-20220458748-Covid-19 vaccine ad26.CoV-2.s -Confirmed clinical vaccination failure. The event(s) has an unknown/unclear 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.