Delayed menstruation after the third vaccination may be caused by pregnancy or endocrine disruption. In clinical practice, the third vaccination does not affect menstruation. 1. Pregnancy: If a woman is not using contraception, she should rule out pregnancy as soon as possible if she experiences delayed menstruation after the third vaccination. 2. Endocrine disorders: Women may suffer from ovarian dysfunction due to various external factors, which may lead to endocrine disorders, thus causing delayed menstruation. Generally speaking, the third vaccination does not affect menstruation, so if women experience delayed menstruation after the third vaccination, they should go to the hospital as soon as possible to rule out the possibility of pregnancy or endocrine disorders.