Vaccines usually do not have long-term side effects, but some people may experience adverse reactions such as allergy, fever, fatigue, gastrointestinal discomfort or redness, swelling and hardness at the injection site. Moreover, vaccines have been proven to be safe and effective by a large number of studies and experimental data before they are applied to the clinic, so they generally do not have long-term side effects. Vaccines are mainly pathogenic microorganisms such as viruses or bacteria and their metabolites that are attenuated and inactivated (almost no effect on the human body) to stimulate the human immune system to produce antibodies and other protective substances, and when the pathogen is re-infected with the human body, the antibodies that have already been produced will produce an immune response. Short-term adverse reactions such as fever, fatigue, allergy and swelling and pain at the injection site may occur in some people after vaccination, which is normal. Vaccines only have their significance in preventing disease if the benefits outweigh the harms to the human body, so there is no need to be overly anxious, if you meet the conditions of vaccination, normal vaccination can play a certain degree of protective effect.