hemolytic crisis in previously known hereditary spherocytosis; this is a spontaneous report received from a contactable reporter(s) (physician) from the regulatory authority. regulatory number: at-basgages-2021-077689 (agency). a 29 year-old male patient received bnt162b2 (comirnaty), intramuscular, administration date 21dec2021 (lot number: fk6304) as dose 3 (booster), single for covid-19 immunisation. relevant medical history included: "hereditary spherocytosis", start date: 1992 (ongoing). the patient's concomitant medications were not reported. vaccination history included: comirnaty (dose 1, single), for covid-19 immunization; comirnaty (dose 2, single), for covid-19 immunization. the following information was reported: haemolysis (hospitalization, medically significant) with onset 27dec2021, outcome "recovering", described as "hemolytic crisis in previously known hereditary spherocytosis". relatedness of drug to reaction(s)/event(s) : health care professional / who assessment /probable/likely no follow-up attempts are possible. no further information is expected