OAKLAND, Calif., Feb. 8 (UPI) -- Protection against whooping cough provided by a vaccine booster shot drops significantly after two years, and to less than 10 percent after four years, according to a recent study.
Kaiser Permanente researchers said the Tdap booster showed decreasing efficacy in the years after it was given to teenagers who have only received newer versions of the five-part DTaP vaccine that prevents whooping cough, tetanus and diphtheria.
The current DTaP vaccine came into use during the 1990s, replacing the DTwP that had been used since the 1950s. The newer vaccine uses proteins from the pertussis bacteria, instead of whole inactivated cells, in order to bypass side effects of the original version.
Outbreaks of whooping cough in recent years have been blamed not only on incomplete rounds of vaccination, but also on its efficacy waning over time.
DTaP is given to children at 2, 4, and 6 months of age, with booster shots between 15 and 18 months old and between 4 and 6 years old, for full protection against the diseases. Tdap is recommended as an additional booster for children between age 11 and 12
"The strategy of routinely vaccinating adolescents to prevent future disease did not prevent the 2014 epidemic, arguably because the protection afforded by a dose of Tdap was too short-lived," Dr. Nicola Klein, co-director of the Kaiser Permanente Vaccine Study Center, said in a press release. "While awaiting development of new vaccines that will provide longer-lasting protection against pertussis, we should consider alternate Tdap immunization strategies for adolescents."
For the study, published in the journal Pediatrics, researchers analyzed 1,207 pertussis cases among adolescent members of Kaiser Permanente Northern California's managed care who were vaccinated with DTaP vaccine between 2010 and 2014.
Researchers found the booster protected 69 percent of teens against whooping cough, which dropped to 57 percent adolescents in the second year, 25 percent in the third year, and about 9 percent in the fourth year.
Klein said the study suggests shifting the schedule of vaccines for Tdap, possibly giving it every three or four years at all ages, as a way to better prevent infection.
"It provides moderate protection during the first year but years two and three after vaccination, there is not that much protection left," Klein told CNN. "The idea of giving the booster to 11- and 12-year-olds -- the recommendation, and in California, the requirement -- is to prevent infections and outbreaks, and that is unfortunately not what we found."