Pertussis vaccine trials in the 1990s.

The significant burden of disease due to pertussis, which predominantly affects newborns during their first few months of life, was substantially decreased following the introduction of inactivated whole-bacterial-cell vaccines in the middle of the 20th century. Although these vaccines were effective in reducing the incidence of pertussis in the countries that implemented their widespread use, increasing concerns about pertussis vaccine-associated adverse events led the development of acellular pertussis vaccines containing 1 or more purified Bordetella pertussis proteins. During the 1990s, collaborative international clinical trials were conducted to evaluate the safety, immunogenicity, and/or efficacy of different acellular vaccines.