First of all, cats will be infected with deadly viruses because they don't have enough antibodies to deal with external bacteria and viruses.
Second, the cat's body may be stunted due to lack of antibodies.
Third, cats may develop antibodies to some viruses they are infected with, but this virus is very likely to be transmitted to humans. The ingredients of the vaccine are antigens. After it is injected into the cat, it stimulates the cat to produce corresponding antibodies. After the next encounter with the same virus, it can produce preventive antibodies and other chemicals that can effectively decompose the virus.
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