The possible reasons why vaccinated cats get feline distemper are: firstly, the antibodies in the vaccinated cats are not fully established; secondly, the vaccinated cats have low antibody levels; thirdly, the vaccinated cats have low levels of antibodies in their bodies; , due to the reduced resistance and immunity of the diseased body. Therefore, it is recommended to check the antibody concentration in the cat one to two weeks after the cat is vaccinated. If the concentration is too low, a supplementary vaccine is required.