late period; this case was received via ra (reference number: gb-mhra-adr 26653378) on 27-feb-2022 and was forwarded to moderna on 27-feb-2022. this regulatory authority case was reported by a consumer and describes the occurrence of menstruation delayed (late period) in a female patient of an unknown age who received mrna-1273 (moderna covid-19 vaccine) (batch no. 3004737) for an unknown indication. no medical history information was reported. on 18-dec-2021, the patient received dose of mrna-1273 (moderna covid-19 vaccine) (unknown route) 1 dosage form. on 03-jan-2022, the patient experienced menstruation delayed (late period) (seriousness criterion medically significant). at the time of the report, menstruation delayed (late period) had not resolved. the patient had 3 vaccinations in total, two pfizer and then a moderna booster shot. each of these had caused delay to her period up to a minimum of 2 weeks late. the moderna booster vaccination had caused her period to be delayed by over a month then and still continued. there were no signs of ovulating but she do had mild to severe cramping on random days. the cramping had been on and off for the last 2 weeks. the patient doesn't think that, this reaction occurred as a result of a mistake made in the administration of the vaccine. drug: covid-19 vaccine moderna, reason: n/a reaction: late period no concomitants were reported. no treatment information was reported. company comment: this is a regulatory case concerning a female patient of unknown age with a history of delayed menstruation with two previous vaccine doses (reported as pfizer vaccine, with an interchange of vaccine product), who experienced the unexpected serious (medically significant) event of menstruation delayed, of approximately one month duration, 16 days after the booster dose of mrna-1273 vaccine. the patient also experienced concurrent cramping. the mentioned medical history remains as a confounder. the benefit-risk relationship of mrna-1273 vaccine is not affected by this report. event�s seriousness assessed as reported.; sender's comments: this is a regulatory case concerning a female patient of unknown age with a history of delayed menstruation with two previous vaccine doses (reported as pfizer vaccine, with an interchange of vaccine product), who experienced the unexpected serious (medically significant) event of menstruation delayed, of approximately one month duration, 16 days after the booster dose of mrna-1273 vaccine. the patient also experienced concurrent cramping. the mentioned medical history remains as a confounder. the benefit-risk relationship of mrna-1273 vaccine is not affected by this report. event�s seriousness assessed as reported