The evolution of pertactin expression in Belgian circulating <i>B. pertussis</i> strains, pre- and post-COVID-19

During the COVID-19 pandemic, non-pharmaceutical intervention measures prevented the spread of other diseases, such as whooping cough (caused by <i>Bordetella pertussis</i>). Now that the use of anti-COVID measures has reduced, many countries have seen a return of infections with <i>B. pertussis</i>. Whereas pre-pandemic, a large part of these strains did not express pertactin, a component used in the pertussis vaccine, now most strains do. A large part of Belgian <i>B. pertussis</i> strains did not express pertactin before the COVID-19 pandemic. We found several different genetic mechanisms as the cause of this. During the pandemic, cases dropped to almost non-existent. Upon their return around 2023, strains showed less genetic diversity, and all expressed pertactin. Our findings illustrate how pertussis epidemiology can be unpredictable and change quickly. Genetic changes in the bacteria can have an effect on vaccine effectiveness and immunity; therefore, it is important to study these changes and maintain epidemiological surveillance.