Pertussis (whooping cough) is making a comeback in the United States. The disease is caused by the bacterium Bordetella pertussis, and a series of DTP (diphtheria-tetanus-pertussis) vaccines is used to prevent it. The original vaccine (DTwP) was prepared using whole-cell pertussis. However, complaints of side effects (fever and, rarely, febrile seizures) and unsubstantiated claims of neurological damage led manufacturers to produce an acellular version (DTaP)*. Unfortunately, the DTaP vaccine does not provide as long-lasting immunity as the previous version. Today, society is reaping the consequences of this decision.
In April 2012, Washington State declared a pertussis epidemic. As of June, pertussis incidence was 37.5 cases per 100,000 population in Washington, compared to 4.2 per 100,000 population in the rest of the United States. Though the incidence is higher in Washington, the age-group trends observed within the state match the observations nationwide. (See chart.)
As shown in the figure, the number of cases is highest for infants less than 1 year old (because they have not received the full series of vaccines, yet) and for children aged 10, 13 and 14. Children get a booster shot at ages 11-12, and this is likely responsible for the drop in incidence at that age. However, at ages 13-14, the incidence creeps back up, indicating that immunity is quickly lost. Children older than 16 years likely received the whole-cell DTwP vaccine, which appears to confer greater immunological protection.
Another factor contributing to the pertussis epidemic is the cyclical nature of pertussis outbreaks. Unvaccinated children appear to play only a minor role.
The lesson to be learned: People who engage in unsubstantiated fearmongering about the safety of vaccines endanger our public health system. Quixotic decisions about vaccine manufacturing have real, and sometimes deadly, consequences.
*Kenneth J. Ryan and C. George Ray, editors. Sherris Medical Microbiology, 4th ed. (New York: McGraw-Hill, 2004.) P. 406.
Source: Centers for Disease Control and Prevention. “Pertussis Epidemic - Washington, 2012.” MMWR 61 (28): 517-522.