The search for a vaccine to prevent pertussis began in 1906, when two French bacteriologists isolated the bacterium responsible for infection. In the 1940s, experimental pertussis vaccines were successful in producing a protective immune response in humans. The first pertussis vaccine was licensed for use in the United States in 1948. These early pertussis vaccines were made from killed whole bacteria. According to the National Institutes of Health (NIH) and the Centers for Disease Control and Prevention (CDC), subsequent widespread use of the vaccine (known as the DTP vaccine) contributed to a dramatic decline in cases of the disease in the United States, which reached an all-time low of just over 1,000 cases in 1976.
Although the vaccine was extremely effective in controlling pertussis, it was associated with some serious side effects, such as fever and rare seizures that eventually discouraged some parents from having their children immunized. In addition, the number of pertussis cases was increasing in the United States by the early 1980s. In response to these concerns, the public health community set out to develop an improved pertussis vaccine that would be equally effective, but with fewer side effects.
Encouraging findings in the late 1980s and early 1990s eventually led to the 1996 licensing of the DTaP vaccine series. The acellular pertussis vaccine uses a form of the bacterium without its cell wall that doesn't cause the adverse effects that the whole-cell predecessor did. According to the CDC, DTaP is a safer version of the older DTP vaccine, which is no longer used in the United States.