It is possible to get whooping cough even if you have been vaccinated with the DPT vaccine. The vaccine is not 100% effective, and a small percentage of the population may fail to receive the vaccine, and the effectiveness of the vaccine decreases over time. The DPT vaccine consists of three vaccines: pertussis, diphtheria, and tetanus, which provide resistance to the corresponding diseases. According to existing studies, the effectiveness of pertussis vaccination against pertussis is about 85%, but not 100%. There are some people who fail to get vaccinated with DPT vaccine and do not produce effective antibodies, and may be infected with pertussis when exposed to pertussis bacilli. Immunization against pertussis usually lasts for about 6 years after vaccination, but protection decreases over time.