Why is the COVID-19 booster needle still infected after injection? Will the third injection of COVID-19 prevent infection

Why is COVID-19 still infected after being vaccinated? On July 20, several staff of Nanjing Lukou Airport detected COVID-19 positive, and a new round of local epidemic broke out in Nanjing. In addition, Suqian in Suzhou, Zhongshan in Guangdong, Shenyang in Liaoning, and Hexian in Anhui each reported one asymptomatic infected person related to Nanjing. The following small series will bring you COVID-19 vaccine will not be infected, let's have a look!