A 2-month-old baby infected with hepatitis B may not show any symptoms because the child is only 2 months old and immunity is not yet fully established, so even if the baby is infected with hepatitis B it should still be in the immune tolerance period. It is too early to tell if the baby is infected with hepatitis B when it is only 2 months old, because at birth, the contraction of the mother’s uterus may cause some blood to enter the fetus through the umbilical cord, resulting in a transient transient hepatitis B virus surface antigen positivity in the fetus. However, the hepatitis B virus can be neutralized by intramuscular injection of hepatitis B globulin after the child is born, and hepatitis B antibodies can be produced and cleared by three injections of hepatitis B vaccine. Therefore, it is recommended that a two-to-one test be performed as early as 7 months of age and that a diagnosis of hepatitis B be made only if it is indicated by a positive hepatitis B surface antigen at that time. Therefore, there is no way to diagnose the presence of hepatitis B in a 2-month-old baby, much less to determine whether hepatitis B infection is present by the presence of symptoms.