Lead author Dr. Nicola Klein, co-director of the Kaiser Permanente Vaccine Study Center, said the fifth dose of DTaP vaccine is routinely given to children ages 4-6 prior to starting kindergarten.
Klein and colleagues compared 277 children, ages 4-12, who were positive for whooping cough, or pertussis, with 3,318 children who were negative for pertussis and separately with 6,086 matched controls. They assessed the risk of pertussis in children from 2006 to 2011 in California relative to the time since the fifth dose of DTaP.
The study, published in the New England Journal of Medicine, found protection from pertussis after the fifth dose of DTaP vaccine waned more than 40 percent each year.
However, if the initial effectiveness of the fifth dose of DTaP was 95 percent, its effectiveness would decrease to 71 percent after five years, but if the initial effectiveness was 90 percent, it would decline to 42 percent after five years, the study said.
The findings suggest that whooping cough control measures may need to be reconsidered," Klein said in a statement. "Prevention of future outbreaks may be best achieved by developing new pertussis-containing vaccines or reformulating current vaccines to provide long-lasting immunity."