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The antibody can still stimulate a strong memory response to elevate antibody level in a short period of time.

However, Shao said that China is studying on whether it is necessary to carry out booster injections for the elderly with weak immune systems and patients with underlying diseases who have completed immunization for more than 6-12 months, as well as the people who work in high-risk areas. 

https://www.globaltimes.cn/page/202108/1230974.shtml