Effectiveness of Tdap Vaccine in Prevention of Pertussis
Pertussis, which is commonly called whooping cough, is caused by infection with Bordetella pertussis, or occasionally B. parapertussis. Bordetella species are fastidious gram-negative coccobacilli. Transmission occurs through direct contact with discharge from respiratory mucous membranes of an infected person. The incubation period is usually 7-10 days after exposure. Pertussis is highly communicable, infecting 80-90% of susceptible contacts. From the onset of symptoms, the disease can take 6-8 weeks to resolve.
The incidence of infections with Bordetella Pertussis has been increasing in the United States. More than 48,000 cases were reported in 2012. Many of these infections occurred in adolescents who were current with their Tdap vaccination.
Tdap vaccine includes tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis. Immunity to pertussis after vaccination does not appear to be long lasting. According to a matched case-controlled study of patients during a 2012 pertussis epidemic in Washington State, the effectiveness of the Tdap vaccine against pertussis wanes within 2 to 4 years after vaccination. Only 34% of vaccinated adolescents were protected between 2 and 4 years after vaccination. Lack of long-term immunity to pertussis after Tdap vaccination appears to be a contributing factor in the increasing incidence of pertussis infection among adolescents.
Acosta AM, DeBolt C, Tasslimi A, et al. Tdap vaccine effectiveness in adolescents during the 2012 Washington state pertussis epidemic. Pediatrics. 2015;135(6):981-989. doi: 10.1542/peds.2014-3358.
