Failure to receive the third dose of a vaccine will affect the immunization effect of the vaccine, resulting in a lower titer of antibodies and weaker protection compared to those who have completed all vaccinations. The third shot of a vaccine is a booster shot, and common vaccines that require a third shot include the New Crown vaccine, HPV vaccine, and Hepatitis B vaccine. It is only after the third vaccination that the whole process of immunization can be completed and the corresponding diseases can be immunized. In particular, the third dose of the New Crown Vaccine is significantly more effective in preventing viruses than those who have only completed the first two doses. Adverse reactions may occur after vaccination. Common adverse reactions include redness, swelling, pain, hardness of the localized area of vaccination, or transient fever, low-grade fever, dizziness, nausea, fatigue, drowsiness, muscle pain, etc. Generally, the symptoms are mild and can be relieved gradually in a few days after vaccination. Vaccination of any vaccine needs to be injected according to the plan under the guidance of the doctor, do not under-vaccinate or miss the best vaccination time.