Smallpox is feared because smallpox can be prevented by cowpox vaccination, which needs to be administered under the guidance of a medical professional. Smallpox is a kind of infectious disease caused by smallpox virus infection, the patient can show various symptoms such as chills, high fever, malaise, skin damage, etc. It has strong transmission ability and high mortality rate. Smallpox is mainly prevented by smallpox vaccination, and the smallpox vaccine commonly used in clinical practice is the live attenuated vaccine of cowpox virus. As the vaccination of cowpox vaccine can effectively prevent smallpox, there is a saying that smallpox is afraid of cowpox. It should be noted that not all people are suitable to receive cowpox vaccine, such as severe allergies, cowpox vaccination can cause allergic reactions, serious can lead to death, should not be vaccinated; suffering from serious underlying diseases, body organs function is not stable, vaccination may lead to the aggravation of the original condition, should not be vaccinated. After vaccination, we should pay attention to light diet, avoid eating spicy and stimulating food, so as not to reduce the effect of the vaccine. Smallpox is currently the only infectious disease that has been eradicated, and there is a certain risk associated with cowpox vaccination, so this vaccine is not used as a routine vaccination at present.