Newer whooping cough vaccines less effective than older vaccines

Teenagers who received DTaP (acellular pertussis vaccine) in their first 2 years of life had a 6 times higher risk of contracting pertussis compared with those who received DTwP (whole-cell pertussis vaccine) in their first 2 years of life, according to a study online in Pediatrics.

Nicola Klein, MD, PhD, and colleagues at the Kaiser Permanente Vaccine Study Center in Oakland, conducted a case-control study among individuals born from 1994 to 1999 who received 4 pertussis-containing vaccines during the first 2 years of life at Kaiser Permanente Northern California (KPNC). The researchers separately compared pertussis polymerase chain reaction (PCR)-positive cases with PCR-negative and KPNC-matched controls. Risk of pertussis relative to vaccine type in early childhood (4 DTwPs, mixed DTwP/DTaP, or 4 DTaPs) by using conditional logistic regression stratified for calendar time and adjusted for gender, race, medical clinic, and reduced antigen content acellular pertussis (Tdap) vaccine status, were also assessed. 


“Among teenagers who received 4 doses of DTaP, receipt of the Tdap booster did not overcome the advantage in protection from pertussis associated with previously receiving DTwP vaccines,” said Dr Klein, a research scientist at the KPNC Division of Research; co-director of the Kaiser Permanente Vaccine Study Center; and clinical instructor in the department of pediatrics, Lucile Salter Packard Children’s Hospital at Stanford, Stanford University School of Medicine.

During the 1990s, the United States switched from combined diphtheria, tetanus toxoids, whole-cell pertussis (DTwP) vaccines to combined acellular pertussis (DTaP) vaccines due to safety concerns, Dr Klein told Formulary.

“The Kaiser Permanente Vaccine Study Center has conducted earlier studies on the waning effectiveness of the DTaP vaccine and noted that pertussis incidence markedly declined among older teenagers,” she said.

Following a 2010-2011 pertussis outbreak in California, Dr. Klein and colleagues sought to evaluate whether disease risk differed in patients aged 10 through 17 years who previously received DTwP from those who received DTaP.

"Despite high levels of vaccine coverage, since the 1980s pertussis epidemics have arisen every 3 to 5 years, with progressively higher incidence rates over time,” Dr. Klein said. “Early clinical trials comparing DTwP with DTaP reported high levels of specific antibody titers and that both vaccines provided good protection against pertussis for several years, yet other studies have suggested that protection following DTaP is less enduring than following DTwP.”

Although reasons for the recurrent pertussis outbreaks are likely to be complex, Dr. Klein said, waning protection following 5 doses of DTaP plays a central role, as least in recent epidemics. Since 2005, the Advisory Committee on Immunization Practices has recommended boosting with reduced antigen content acellular pertussis (Tdap) vaccine for persons aged 11 years and older.

“This study demonstrates that teenagers who received DTwP during the first 2 years of life were more protected against pertussiss than were teenagers who received DTaP,” she said. ”Despite these findings, use of the booster vaccine Tdap is still the best available means to help protect the DTaP-only group of adolescents and teenagers from pertussis. Research into developing new pertussis vaccines with improved safety and long-lasting immunity is warranted.”