The incubation period of hepatitis B virus refers to the period of time from the invasion of hepatitis B virus into the body until the first clinical symptoms appear. The length of the incubation period depends mainly on the number of infected hepatitis B viruses, their virulence and the immune status of the body. After infection with hepatitis B virus, there are different clinical types due to viral factors, organismal factors and environmental factors. In children infected with hepatitis B virus, 20% become chronic hepatitis B virus carriers or chronic hepatitis B; while only 3%-6% of adults infected with hepatitis B virus develop chronic hepatitis B, or chronic hepatitis B virus carriers. Hepatitis B patients and hepatitis B virus carriers are the main source of hepatitis B virus infection.