In adolescents who have received DTaP vaccines as infants, the Tdap vaccine offers moderate protection against whooping cough during the 1st year after vaccination, but effectiveness decreases to less than 9% after 4 years, according to a study published in Pediatrics.
During the 1990s, clinicians in the United States started vaccinating children with DTaP (diphtheria, tetanus, and pertussis) vaccines, replacing the older whole cell pertussis (DTwP) vaccine used previously. Despite high rates of vaccine coverage, the number of whooping cough cases in the United States and other countries has increased since the switch.
To combat the rise in whooping cough, the Advisory Committee on Immunization Practices recommended that all adolescents aged 11 to 12 years get a booster Tdap vaccine, starting in 2006.
To explore the Tdap (tetanus-diphtheria-acellular pertussis) vaccine’s efficacy during outbreaks, the study included only adolescents vaccinated with Tdap who received the DTaP vaccine for all 5 rounds of childhood immunization, specifically focusing on the 2010 and 2014 outbreaks of whooping cough in Northern California.
Using 1,207 pertussis cases, the researchers found that Tdap vaccine efficacy was 68.8% during the 1st year after vaccination. The efficacy rate decreased to 8.9% 4 or more years after vaccination. During the 2014 outbreak, adolescents had the highest incidence of pertussis in any age group despite greater than 90% vaccine coverage among them.
“This study demonstrates that despite high rates of Tdap vaccination, the growing number of adolescents who have received only the newer acellular pertussis vaccines continue to be at higher risk of contracting whooping cough and sustaining epidemics,” said Nicola Klein, MD, PhD, co-director of the Kaiser Permanente Vaccine Study Center. “Because Tdap provides reasonable short-term protection, it may contain whooping cough more effectively if it is administered to adolescents in anticipation of a local outbreak rather than on a routine basis at age 11 or 12.”
- Klein NP, Bartlett J, Fireman B, et al. Waning Tdap Effectiveness in Adolescents. Pediatrics. 2016; doi:10.1542/peds.2015.3326.