Some parents’ children come to me in the clinic with the lab report of the five hepatitis B tests. “Doctor, my child was already vaccinated against hepatitis B at birth, why is he still infected with the hepatitis B virus?” . Faced with her face of confusion, I was also full of confusion. The child was currently a teenager, and I had to infer the probable time of infection after a careful examination. Generally speaking, there are several points in time when a teenage child may be found to be infected with the hepatitis B virus: a. The child was infected in utero before birth. Second, the child was born with the infection at the time of delivery and the mother-to-child blockade failed. Third, during the growth of the child after birth. Therefore, mothers with hepatitis B virus infection should have their children retested for the five hepatitis B tests at several critical moments after birth. Intrauterine infection, as the name implies, occurs when the fetus is already in the mother’s womb and the hepatitis B virus is transmitted from mother to fetus. The hepatitis B test can show positive hepatitis B surface antigen and positive hepatitis B virus DNA as soon as the child is born. Of course, medical transmission of the hepatitis B virus is extremely rare. The main reason is that a contaminated amniocentesis was performed. Infection at birth is easily understood, as the child is infected by the birth canal compression, maternal vaginal secretions, amniotic fluid and other body fluids containing hepatitis B virus through the fetus’ damaged mucous membranes. Postpartum infection is the infection of the hepatitis B virus that occurs during the growth of the child. Some people with hepatitis B are infected with the hepatitis B virus early in life, but slow hepatitis B is an infectious disease not a genetic disease. Genetic diseases are diseases that occur at the genetic level, especially dominant genetic diseases, and diseases are mostly inevitable after birth and cannot be prevented by some medical means at this time. Infectious diseases require three basic elements to occur: the source of infection, the route of transmission, and the susceptible population. This is why people often confuse infectious diseases with genetic diseases in their lives. Hepatitis B markers can be checked at birth before the child is given the hepatitis B immunoglobulin and hepatitis B vaccine to determine if the child has developed an intrauterine infection. If the hepatitis B surface antigen and hepatitis B surface antibody are both negative, the child is not infected with the hepatitis B virus and has not developed protective antibodies against hepatitis B. This requires a booster vaccination. If the child is found to be positive for hepatitis B surface antigen, it is necessary to check the hepatitis B viral DNA load. If the hepatitis B viral load exceeds the normal range, it means that the mother-to-child blockade of hepatitis B has failed. If, unfortunately, hepatitis B infection has already occurred, we can opt for antiviral treatment if appropriate for the child. The earlier the hepatitis B virus infection occurs, the greater the probability of cirrhosis or liver cancer if left untreated. After the child has successfully developed protective antibodies (hepatitis B surface antibodies) from mother-to-child blockade, all is not lost because the titer of antibodies will continue to drop with age. When the titer of antibodies drops below 10, there is also the possibility of chronic infection if the hepatitis B virus is encountered again, so we should not take this lightly and need to review the five indicators of hepatitis B every three to four years. For domestic vaccines, it is recommended that the Hepatitis B quantification be reviewed once every 5-6 years after antibody production, and for imported vaccines, the Hepatitis B quantification can be reviewed once every 7-8 years. One of the reasons why there is a difference is that the number of Chinese hepatitis B carriers and chronic hepatitis B patients is so large that we have more chances to be exposed to the virus and some of the antibodies are consumed after they are produced, but there is no need to worry, as long as the body can produce antibodies normally, if we are exposed to a large amount of hepatitis B virus, it will stimulate the body to produce a large amount of antibodies. This is the result of our active immunity. If you have been accidentally exposed to the hepatitis B virus and are not sure if you have antibodies, you can go to a hospital or CDC and get an injection of hepatitis B immunoglobulin to block the hepatitis B virus through passive defense.