Planned immunization and vaccination is the most effective measure to control and eliminate infectious diseases, the national schedule of planned immunization is as follows: babies are vaccinated with BCG and hepatitis B vaccine at birth, the second dose of hepatitis B vaccine at full term, polio trivalent mixed vaccine at the age of 2, 3 and 4 months; at 3, 4 and 5 months of age, the mixed vaccine against leucovorin, and at the 6th month The third dose of hepatitis B vaccine is given at the age of 8 months, the MMR vaccine at the age of 1.5-2 years, the fourth dose of mixed polio vaccine at the age of 4 years, the fourth dose of trivalent polio vaccine at the age of 4 years, and the second dose of BCG and measles vaccine at the age of 6-7 years, as well as the mixed polio vaccine.