The third vaccine is generally referred to as the third dose of the new coronary vaccine and is necessary. Our current vaccination is mainly the inactivated vaccine against the new coronavirus. After the new coronavirus vaccination, the protective effect of the vaccine on the human body will be reduced with the passage of time, so it is very necessary to have the third vaccination. It can effectively stimulate the body to produce new antibodies again, which has a reinforcing effect on the prevention of the new coronavirus. Except for pregnant women, people who are not suitable for vaccination such as those who are suffering from acute illnesses and neurological disorders, it is recommended that all others complete the third vaccination within the prescribed time. At present, the booster shot of inactivated vaccine in China is mainly given to people over 18 years of age who have no contraindications to vaccination. The side effects of the third vaccination are similar to those of the first two, and some people may experience redness and swelling of the skin and slight fever after vaccination, which are natural reactions after vaccination and usually return to normal in about 48 hours. If the adverse reaction worsens after vaccination or there are other physical symptoms, it is recommended to go to the hospital immediately to find out the cause and treat the cause.