Pertussis vaccines effective against pertactin-deficient strains

Immunity to pertussis from either natural infection or vaccination, is not lifelong. Two acellular pertussis vaccines are in widespread use in the United States, and they differ in the number and amounts of purified proteins and method of being chemically inactivated. A vaccine made by GlaxoSmithKline includes three proteins: pertussis toxin (PT), filamentous hemagglutinin (FHA), and pertactin (PRN). A vaccine made by Sanofi Pasteur includes the same three proteins (PT, FHA, and PRN) plus two types of fimbriae (FIM), for a total of five ingredients. PT causes virtually all the symptoms of pertussis disease. The other proteins included in the two acellular vaccines are principally there to prevent the Bordetella pertussis bacteria from attaching to the nasopharynx and lung because prevention of attachment is a prevention of pathogenesis.

Although both acellular pertussis vaccines provide good protection, many reports support that acellular pertussis vaccines have shown waning immunity. One hypothesis among experts is that waning immunity might be related to changes in the protein structure of one or more of the targets for acellular vaccines. The protein that has been shown to have changed since introduction of acellular vaccines is PRN.

In the current study from Vermont, we learn that acellular pertussis vaccine efficacy remained high in that state despite the presence of over 90% of the B. pertussis strains lacking a PRN protein on the bacteria surface that would serve as an antibody target following vaccination. In other words, the lack of PRN as a vaccine target did not reduce vaccine efficacy nor did it impact the waning immunity following vaccination.

The result is reassuring and expected. All bacteria that seek to attach themselves to our respiratory tract in the nose or lungs or both have many different proteins to accomplish that attachment task. The redundancy of those proteins fits easily in a biologic necessity framework because pathogenesis cannot begin for any of the respiratory pathogenic bacteria unless they can attach themselves to the host in the nose or lungs or both. The addition of FHA as well as PRN in the GlaxoSmithKline vaccine and FHA plus two types of FIM antigen as ingredients in the Sanofi Pasteur vaccine was to raise antibody to multiple “adhesion” proteins. That way if “escape mutants” occurred, as we are now observing for PRN-deficient strains, the vaccines would still work. The study from Vermont tells us that they still do work.

Michael E. Pichichero, M.D., a specialist in pediatric infectious diseases, is director of the Research Institute, Rochester (N.Y.) General Hospital. He is also a pediatrician at Legacy Pediatrics in Rochester. Dr. Pichichero commented in an interview. He said he had no relevant financial disclosures.