Viral hepatitis A, referred to as hepatitis A and hepatitis A, is an infectious disease caused by the hepatitis A virus (HAV), with inflammatory lesions of the liver as the main cause, mainly through the fecal-oral route of transmission. Clinically, fatigue, loss of appetite, hepatomegaly, and abnormal liver function are the main manifestations, and jaundice is seen in some cases. The main manifestation is acute hepatitis, and asymptomatic infection is common. The disease can develop at any age, but mainly in children and adolescents. The clinical symptoms of hepatitis A in adults are generally more severe than those in children. The peak of hepatitis A incidence is often in winter and spring. The disease is self-limiting and non-chronic, causing acute severe hepatitis, which is extremely rare. The vaccine may cause the body to produce antibodies, antigenic reactions. Signs of a serious reaction to hepatitis A vaccination include the following: 1. high fever; 2. behavioral changes; 3. difficulty breathing; 4. hoarseness or wheezing; 5. hives; 6. pallor; 7. weakness; 8. rapid heartbeat; 9. dizziness. Other mild reactions to hepatitis A vaccine that may last for 1 or 2 days include: 1. pain at the injection site; 2. headache; and 3. fatigue. However, most vaccinees do not experience adverse reactions in clinical practice. If adverse reactions do occur, continued observation is recommended, and fever can be treated with antipyretic medication. Vaccines are all derived from viruses, which means they are viruses themselves. After vaccination, fever is a kind of self-protection. You don’t need to deal with it if it doesn’t exceed 38°C. If it exceeds 38°C, you can take antipyretic agents. However, try not to use anti-inflammatory drugs such as antiviral treatment, which can destroy the effect of the vaccine and lead to vaccination failure. If the symptoms do not ease or worsen, you should promptly go to the hospital for treatment. In a few cases, local pain, redness and swelling may occur after vaccination, which will generally resolve on its own within 72 hours. In rare cases, a rash may appear, which does not require special treatment, and if necessary, consult a doctor or treat the symptoms.