The itchiness of the third vaccination can be caused by adverse reactions to the vaccine, local allergies and local infections. 1. Adverse reactions to the vaccine: Although the safety of the third injection of the new crown vaccine is relatively high, there are still some people who will have adverse reactions after vaccination, the more common is the itching at the site of vaccination, which is a normal phenomenon and can be relieved after 1-3 days. 2. Local allergy: If you are allergic, the itchiness of the third injection of the new crown vaccine is usually due to a local allergic reaction. 3. Localized infection: You should not take a bath within 24 hours after the third injection of the new crown vaccine, and you should also avoid sweating a lot, if you do not pay attention to these aspects, it may cause infection at the vaccination site, resulting in itching. If patients with the third injection of the new crown vaccine itching, if the symptoms are mild do not need special treatment, if the symptoms are serious, it is recommended to go to the hospital in a timely manner, and actively cooperate with the doctor for treatment.