The third dose of the New Crown vaccine may have side effects such as redness, swelling, pain, and itching at the site of vaccination, as well as malaise, drowsiness, and transient febrile reactions. The third shot of the new crown vaccine may be the third booster shot of the inactivated vaccine or the third shot of the recombinant subunit vaccine. The main purpose of the third vaccination is to increase the serum level of antibodies against New Crown virus and to enhance the preventive effect against New Crown pneumonia. The booster shot of the new crown vaccine is harmless after vaccination. Some people may have adverse reactions such as redness, swelling, pain and itching at the site of vaccination, as well as malaise, drowsiness, and transient febrile reactions after vaccination. However, these reactions are generally mild and can subside on their own, and will not adversely affect daily life. After the third vaccination, if the adverse reactions such as redness and swelling at the vaccination site continue to worsen or are not relieved, it is recommended that the patient consult a doctor in time for help. Tip: The terms “new coronavirus pneumonia and new coronavirus pneumonia” mentioned in this article were renamed to “new coronavirus infection” on December 26, 2022, as announced by the National Health Commission.