Diarrhea can last for 2-3 days after vaccination, but it depends on the physical condition and care of the vaccinated person. Diarrhea caused by vaccination is a relatively common post-vaccination adverse reaction, which is usually mild and can recover on its own without special treatment. After vaccination, the immunogenicity of the vaccine induces an immune response in the body, which may have certain effects on various systems and may cause diarrhea in people with unstable gastrointestinal function. Some people recover after 1-2 episodes of diarrhea, while those with more severe diarrhea may have more frequent and longer duration, usually not more than 3 days, but it does not exclude that diarrhea lasts longer in poorer people. Good care can help improve diarrhea by drinking warm water to help reduce irritation of the gastrointestinal tract and prevent dehydration due to diarrhea. Hot towels or hot water bags can be used, but be careful to control the temperature to avoid burns, and gentle massage of the abdomen can also help improve diarrhea. If it is more serious, it is recommended to seek medical treatment and, if necessary, take antidiarrheal medication such as montelukast as prescribed by the doctor. In addition, if the diarrhea is not relieved for a long time, or if there are more obvious accompanying symptoms such as fever and abdominal pain in addition to diarrhea, it is possible that the intestinal tract is infected by bacteria or viruses, and it is necessary to promptly consult a regular hospital gastroenterology department. The diagnosis is usually made through routine stool tests, and timely antidiarrheal and anti-infective treatment is given. At the same time, electrolytes such as sodium and potassium should be replenished to prevent electrolyte disorders and dehydration. Adverse reactions such as fever, dizziness and headache may occur after vaccination.