The main reasons for infection after vaccination include infection with other strains of virus and failure to produce sufficient antibodies after vaccination. 1. Infection with other strains of viruses: because the vaccination strain is not consistent with the infected strain of virus, the infected strain of virus has mutated, so even after vaccination, it will still be infected. 2. Failure to produce sufficient amount of antibodies after vaccination: Due to the low immune function of some vaccinated people, they do not produce sufficient amount of immune response after vaccination, or the number of vaccines received is insufficient, resulting in a decrease in the body’s immune ability, and they will also be infected again. Or the antibody level in the body has dropped after a long time of vaccination. Therefore, if you are infected after vaccination, it is best to consult a doctor in a timely manner, analyze the situation of your own body, and treat according to the advice of a professional doctor.