If a vaccination is administered when there is no fever, there is a risk of adverse reactions, and the most common systemic symptom of these adverse reactions is fever. Although the probability of this symptom is high and low, most of them are relatively low, but if the fever occurs again at the time of fever because of vaccination, the two causes of fever together can make the fever worse, so vaccination is less recommended at the time of fever. If the vaccine is administered without causing such systemic adverse reactions in patients with fever, the corresponding fever symptoms will not be significantly worse, but this is not very easy to distinguish clearly, so it is still recommended to administer the vaccine when it is completely normal and without any discomfort. In the case of lethal diseases, such as rabies, vaccination is recommended even if there is a fever, as timely vaccination allows the body to produce antibodies in a timely manner.