New Delhi – The Covid-19 vaccinations did some harm along with some good to people, especially women as they complained of irregular periods. The paper – “Understanding the trauma of menstrual irregularity after Covid vaccination: a bird’s-eye view of female immunology” – has compiled data from the reports of three countries showing significant figures on this subject. A US cohort of 2,403 females showed that 55 per cent of females receiving the Pfizer vaccine, 35 per cent relating to Moderna and 7 per cent linking to Johnson and Johnson/Janssen vaccine underwent changes in their cycle length. The Norwegian young adult cohort also informed heavier bleeding, increase in duration of menstruation and even shortening of interval between two cycles. In the UK cohort of 39,591 females, menstrual disturbances were also testified.