Bordetella pertussis,
a Gram-negative bacterium, causes whooping cough (pertussis) in humans.
Vaccination against pertussis was first introduced in the 1950s. The
coverage of primary vaccination has been high in industrialized
countries where acellular vaccines (ACVs) are commonly used. In many
developing countries, the vaccination coverage is increasing and
whole-cell vaccines (WCVs) are mainly in use. WCVs include inactivated
whole bacteria, whereas ACVs comprise purified antigens including
pertussis toxin (Ptx), filamentous hemagglutinin, pertactin (Prn),
fimbriae (Fim) 2 and Fim3 in different combinations and concentrations.
Compared with WCVs, ACVs are less reactogenic and are also used for
booster vaccinations in older children and adults. Despite extensive
vaccinations, pertussis has resurged in industrialized countries since
the beginning of the 21st century.^{1–3(external)}
Major explanations for the resurgence are waning immunity associated
with ACVs and bacterial adaptation to vaccine-induced immunity. Compared
with the vaccine strains, continuous changes have been observed in
genomes of B. pertussis circulating in immunized populations. Common methods used for surveillance of B. pertussis
isolates include serotyping, genotyping for vaccine antigens and
genomic analyses by multilocus variable number of tandem repeat analysis
(MLVA) and pulsed-field gel electrophoresis (PFGE).^4(external) More recently, whole genome sequencing has been applied.^5(external),^6(external) Many studies demonstrate that variation of B. pertussis occurs in both phenotypes and genotypes.