Active vaccine refers to the mutation of disease-causing bacteria or viruses through artificial intervention, so that they lose their pathogenicity and retain their immunogenicity, and after inoculation, they can cause the body to produce immunity without causing illness.
Active vaccines, also known as live attenuated vaccines, retain antigenic activity after losing pathogenicity, reproduce naturally in the body after inoculation close to natural infection, and stimulate antigen-antibody reactions to produce long-lasting immunity without causing disease in the body. The common BCG vaccine, measles vaccine, polio vaccine, etc. are all active vaccines.
In short, active vaccines, i.e., attenuated pathogens, do not cause only mild clinical reactions while exerting lasting immunity to pathogens, so there is no need to be overly anxious.