After a lull during the COVID-19 pandemic, pertussis (whooping cough) has made a resurgence—especially in adolescents—with larger outbreaks than those seen during recent peaks in many countries, according to a summary of an online workshop organized by the International Bordetella Society in mid-November.
While most countries didn’t experience significant declines in pertussis vaccination during the pandemic, better vaccines may be needed to more fully protect against infection and curb disease transmission of circulating strains, the authors said.
Workshop attendees presented pertussis surveillance data from Australia, Japan, China, South Africa, France, the Czech Republic, Denmark, Finland, England, Argentina, and the United States. This international group, led by UK Health Security Agency researchers, wrote the resulting special communication, published this week in JAMA Network Open.
Sustained high vaccine uptake
Caused by the Bordetella pertussis bacterium, pertussis is a highly contagious disease that causes a prolonged forceful cough in all age-groups and is a life-threatening disease in young infants. While pertussis vaccines made of inactivated whole-cell B pertussis bacteria have been used for decades, the adverse reactions they can cause led to the development of acellular vaccines, or those made from isolates from the bacterial antigen.
B pertussis continues to circulate and the resulting population immunity plays a role in pertussis disease prevention.
The World Health Organization continues to recommend whole-cell pertussis vaccines, which are used in most lower-income countries, while most higher-income countries use acellular vaccines. Acellular vaccines are recommended for pregnant women in many countries.
“Despite sustained high vaccine coverage, peaks of pertussis disease continue to occur every 3 to 5 years in some countries, indicating that B pertussis continues to circulate and the resulting population immunity plays a role in pertussis disease prevention,” the study authors wrote.
Cases grew 19-fold in French kids aged 5 to 14
The researchers noted that, before the pandemic, several countries—particularly those that used acellular pertussis vaccines in infants—reported circulating B pertussis isolates that lacked pertactin, the acellular vaccine antigen that enables the bacteria to attach to cells. But recently, most isolates have expressed this antigen, and several countries have observed an increase in B pertussis isolates resistant to macrolides, a class of broad-spectrum antibiotics.
From 2019 to 2024, the proportion of pertussis cases in children aged 5 to 14 years rose in Australia (from 41.4% to 57.7%), Czech Republic (7.4% to 21.1%), France (23.0% to 31.5%), Finland (25.8% to 36.7%), and England (18.7% to 29.3%). The proportion of cases in infants younger than 1 year was comparable or reduced when comparing 2019 with 2024, indicating that infant and maternal vaccines likely remained effective in that age-group.
As an example, France reported almost no cases of pertussis during the COVID-19 pandemic. Cases began to rise in 2023, when 510 cases were recorded, reaching 5,072 by May 31, 2024, and 36,938 by the end of December 2024.
During the same period, France reported 42 pertussis deaths, 20 of them in infants. About half of prepandemic isolates from 2016 to 2020 were pertactin-negative, and less than 30% were positive for FIM2 (protein subunit of B pertussis that helps bacteria attach to cells). But starting in 2023, 96% expressed pertactin, and 76% were FIM2-positive.
Another troubling finding, the authors said, was the detection of 17 macrolide-resistant B pertussis (MRBP) isolates, making up nearly 2% of the samples processed. Of the 14 isolates cultured, genomic and microbiologic analyses identified them as belonging to an MRBP lineage circulating in China; unlike most isolates from 2024, 93% of these isolates were deficient in pertactin.
From 2019 to 2024, cases in France grew 13.1-fold, with an 18.7-fold rise in children aged 5 to 14 years. The overall rate was 58 per 100,000 people, but it was 245 per 100,000 in children aged 1 to 4 years, followed by children younger than 1 year, at 150 per 100,000, and those aged 5 to 14 years (149 per 100,000).
Fewer asymptomatic infections to boost immunity
While some countries recently introduced new diagnostic multiplex testing, it had largely begun before the pandemic, indicating that changes in case numbers were not due to only diagnostic differences, the authors added.
The data presented herein suggest a need for new pertussis vaccines that protect against both disease and infection and that reduce transmission.
Pertussis is endemic worldwide, with periodic peaks of disease, suggesting that transmission of B pertussis continues in vaccinated people, and animal testing also suggests that acellular vaccines have very little effect on disease transmission, the authors said.
In addition, most countries didn’t experience significant declines in pertussis vaccination rates during the COVID-19 pandemic. But with less circulation of B pertussis during the pandemic, there were likely fewer asymptomatic infections to boost immunity, making a larger percentage of the population vulnerable. “This is likely partially responsible for the increases observed in 2023 and 2024,” they wrote. “Both vaccine- and infection-induced pertussis immunity wanes over time.”
“The potential for large outbreaks of pertussis highlights the importance of maintaining or increasing vaccine coverage in pregnancy and in infants and children,” they concluded. “The data presented herein suggest a need for new pertussis vaccines that protect against both disease and infection and that reduce transmission.”
