Current pertussis vaccines were as effective against the rapidly evolving pertactin-deficient strains of the organism as they have been against other strains, according to a report published online April 13 in Pediatrics.

The proportion of pertussis strains lacking pertactin increased markedly in the United States, from 14% in 2010 to 85% in 2012. Pertactin, an autotransporter thought to be “involved in bacterial adhesion to the respiratory tract and resistance to neutrophil-induced bacterial clearance,” is a component of acellular pertussis vaccines. Some have speculated that pertactin deficiency evolved to give the bacteria an advantage in response to vaccine-related selection pressure, and that this evolution has contributed to the recent resurgence of pertussis disease, said Lucy Breakwell, Ph.D., of the epidemic intelligence service, Centers for Disease Control and Prevention, Atlanta, and her associates.

To assess vaccine efficacy in the setting of pertactin deficiency, the investigators studied 820 cases and 2,369 matched control subjects treated in Vermont during a 3-year period encompassing a recent pertussis outbreak there. The study included children aged 4-10 years given the five-dose DTaP childhood series and adolescents aged 11-19 years given the adolescent Tdap dose. Specimens from these cases had been cultured routinely by the state department of health laboratory, and more than 90% of the available isolates were found to be pertactin deficient.

The overall vaccine efficacy of the DTap series was 84%, and of the Tdap booster, 70%. “Remarkably,” these rates are comparable to the 89% efficacy of DTap reported in a 2010 California outbreak and the 64% efficacy of Tdap reported in a 2012 Washington state outbreak, the investigators said. “Our findings suggest that both acellular pertussis vaccines remain protective against pertussis disease in the setting of high pertactin deficiency,” and therefore remain the best method for protecting against severe disease, Dr. Breakwell and her associates said (Pediatr. 2016 April 12. doi: 10.1542/peds.2015-3973 ).

Nevertheless, further study is warranted “to better understand the implications of pertactin deficiency on pertussis pathogenesis and host immunologic response, which could provide insight into the development of novel pertussis vaccines,” they wrote.

This study was supported by the Centers for Disease Control and Prevention. Dr. Breakwell and her associates reported having no relevant financial disclosures.