Whooping Cough Epidemic Hit Vaccinated Kids Hard

Researchers found Tdap vaccine effectiveness fell off after 2 to 4 years. The 2012 pertussis epidemic in Washington state affected a surprising number of adolescents who were vaccinated on schedule, researchers reported. Compared with over 1,200 controls, 450 adolescent cases of pertussis showed similar rates of having received five rounds of their vaccinations on the recommended schedule, but the vaccine's effectiveness rate dropped dramatically over time from 73% within 1 year to as low as 34% after 2 to 4 years from the last dose, Anna M. Acosta, MD, of the CDC, and colleagues, reported in Pediatrics. The study authors hazarded a few guesses as to why vaccine effectiveness fell short. One explanation could be suboptimal, post-vaccination, cell-mediated immunity with the acellular vaccine. Another could be that the vaccine prevented symptoms, but not infection and transmission. Also, there could have been genetic mutations in the pertussis strains that were not accounted for in the vaccine.