Smallpox is a severe infectious disease caused by smallpox virus infection, which is transmitted by inhalation or direct contact. Usually, the infected person will have papules distributed throughout the body on the second day after being exposed to the virus. Then the papules began to be filled with a large amount of clear or milky liquid, like a small bean one by one. The acne gradually turned into pustules, and finally healed on the 16th to 20th day, leaving a scar on the whole body of the infected person. In fact, it's a fluke to live a lifetime with scars. The mortality rate of smallpox is as high as 30%. In patients less than one year old, the mortality rate is 40% - 50%.
This kind of malignant disease has plagued mankind for thousands of years. At present, the earliest evidence of human smallpox infection comes from the mummies of ancient Egypt 3000-4000 years ago. Since historical records, smallpox has taken countless lives, but human beings have never been waiting to die. Although smallpox is a disease with high mortality and difficult to cure, it can be prevented by vaccination. According to historical records, the earliest attempt to vaccinate humans may have come from ancient India about 3000 years ago. In the Ming Dynasty about 500 years ago, the method of vaccination was already used among the people. People collect the liquid and skin of smallpox patients, dry them and grind them into powder, and then plant them in the nasal cavity of uninfected people. However, this method of inoculating smallpox virus with strong pathogenic activity into human body is extremely dangerous. Some vaccinators will have systemic rash after inoculation, which is equivalent to experiencing a complete course of smallpox. Even worse, it will lead to death, which also limits the promotion of smallpox vaccination.
Is it a lifelong fear of smallpox infection or a choice of dangerous vaccination? This dilemma did not change until more than 200 years ago. At that time, a doctor named chener accidentally found that vaccinating cows with vaccinia virus can prevent smallpox, and the adverse reactions are very small. The safety of this method is incomparable to that of directly inoculating smallpox virus. Then this improved method of vaccinating spread rapidly all over the world. In 1958, the World Health Organization (who) decided to put the elimination of smallpox on the agenda. In 1980, the World Health Organization announced that smallpox had been eliminated worldwide. Smallpox virus is the first virus that has been completely extinct by human beings, and smallpox is also the only human disease that has been completely eliminated so far.
Why can posterity gain immunity to smallpox after vaccination? It starts with the way the human immune system works. In the long process of evolution, the human body has developed a set of methods to fight against virus infection. When smallpox virus invades human body for the first time, the immune system of human body does not know the invader. It often takes time to identify the pathogen and mobilize various immune mechanisms to resist the virus invasion. It takes at least a week for the whole body's immune system to be fully mobilized. When the infected person recovers, the immune system will have a "long memory" and remember some characteristics of smallpox virus (usually the proteins on the surface of the virus, which can cause the immune system to respond, are usually called "antigens"). When the same virus invades again, the immune system can quickly recall the past experience by recognizing the characteristics of the virus, and quickly mobilize various immune mechanisms to fight against the invasion and prevent the recurrence.