Pertussis Vaccine Resistance Emerging in the U.S.
Pertussis, an illness characterized by a whooping cough, is
caused by the bacteria Bordetella Pertussis. The disease frequently affects young children and
infants. In the prevaccine era, pertussis was very common and a major cause of childhood mortality
in the United States. Since the institution of routine childhood vaccinations, the incidence of
pertussis has reduced from 150 reported cases per 100,000 persons in 1940, to a low of 0.5 per
100,000 in 1976.1 Since the 1980's, the incidence of the disease has gradually increased
to 13.3 cases per 100,000 in 2012, the highest total since 1955.2
One explanation for the increasing prevalence of pertussis is
the adaptation of the bacteria due to vaccine selection pressure. A mutated, pertactin-negative B.
pertussis strain has been reported in other countries such as France, Finland, and
Japan.3 Pertactin is one of many antigenic components used in the current pertussis
vaccine. Pertactin is a protein that helps B. pertussis attach to the lining of the airways.
Pertactin-negative B. pertussis strains have been found to have similar lethality and
transmissibility compared to traditional strains. A letter published in the New England Journal of
Medicine in February shows the first known occurrence of pertactinnegative B. pertussis strains in
the United States.4 In the letter, researchers analyzed the pertactin genes in 12
isolates of B. pertussis cultured from children hospitalized in Philadelphia during 2011 and 2012.
By the use of Western blotting, they found that 11 of the 12 isolates did not contain the pertactin
protein. Pulsed-field gel electrophoresis showed multiple mutations to the gene encoding pertactin,
resulting in non-expression of the protein. It was concluded that further research is needed in
different geographical regions throughout the United States to determine if their findings are
local, or if a more widespread shift in B. pertussis strains has occurred.
It is important to note that of the 12 B. pertussis isolates
in the report, only two were collected from patients greater than 6 months of age; therefore many
of the subjects were unvaccinated or under-vaccinated. Because of this, it is unknown if
pertactin-negative B. pertussis is more likely to cause disease in individuals who are fully
vaccinated. Although the report confirms that pertactin-negative B.pertussis variants are now in
the United States, it remains to be seen whether this is a major cause of the increasing incidence
The Center for Disease Control (CDC) has acknowledged these
findings. They report that other factors such as increased reporting, awareness, recognition by
clinicians, better lab diagnostic testing, and the vaccine formulation change from whole cell to
acellular in the 1990's are mainly responsible for the increasing incidence. The CDC also reports
that the pertussis vaccine remains effective against the pertactin-negative variants because it
contains other components that produce an immune response. In addition to pertactin, the current
acellular pertussis vaccines also contain combinations of inactivated pertussis toxin (PT),
filamentous hemagglutinin, and fimbriae, each of which can produce an immune response.3
They conclude that the vaccine continues to be a safe and effective tool in the prevention of
1. Faulkner, Amanda. et. al. Chapter 10:
Pertussis. VPD Surveillance Manual. 5th. Center for Disease Control, 2011. 10/1-10/11. E-copy.
2. 2012 Provisional Pertussis Surveillance
Report. Center for Disease Control. January 4, 2013.
61(52). Accessed online: April 3, 2013. Web Address:
3. Pertactin-Negative Pertussis Strains.
National Center for Immunization and Respiratory Diseases, Division of Bacterial Diseases. Last updated February 12, 2013. Accessed Online April 3,
2013. Web Address: http://www.cdc.gov/pertussis/pertactin-neg-strain.html
4. Queenan, AM, PK Cassiday, and A
Evangelista. "Pertactin-Negative Variants of Bordetella pertussis in the United States."
New England Journal of Medicine. 386.6 (2013): 583-584. Web. 4 Apr. 2013.