Why Japan saw a major pertussis surge in 2025 while other countries peaked earlier

By Vijay Kumar MalesuReviewed by Susha Cheriyedath, M.Sc.Apr 20 2026

Pertussis cases dropped during the pandemic, then surged back across several countries, but Japan’s delayed 2025 outbreak stood out for its scale and its heavy impact on older children and teens. The findings raise new questions about waning immunity, booster policy, and how best to protect infants in the post-pandemic era.

Study: Pertussis resurgence after the COVID-19 pandemic in four Western Pacific Countries and the USA, highlighting the 2025 outbreak in Japan. Image Credit: Kateryna Kon / Shutterstock

In a recent study published in the journal Scientific Reports, a group of researchers analyzed post-coronavirus disease 2019 (COVID-19) resurgence patterns of pertussis across multiple countries, with a focus on Japan’s unique 2025 outbreak.

Pertussis Risk, Waning Immunity, and Post-Pandemic Shifts

What happens when pandemic precautions disappear, and do old diseases return stronger? Global public health systems and vaccination strategies control infectious diseases such as pertussis (whooping cough) that were once common and vaccine-preventable.

During the COVID-19 pandemic, strict public health measures reduced the spread of infectious diseases, but once these restrictions were lifted, many countries reported a sharp rise in pertussis cases.

Waning immunity, combined with low booster vaccination rates and evolving bacterial resistance, has made controlling pertussis more challenging. Infants remain at greatest risk; however, the increased incidence of pertussis in teens and adults raises new concerns about transmission dynamics. 

Ongoing research is necessary to further explore changing epidemiologic patterns associated with pertussis and develop effective prevention strategies.

Multi-Country Pertussis Surveillance Study Design

The present retrospective study used publicly available national pertussis surveillance data from Japan, Australia, New Zealand, China, and the United States of America (USA).

Data were collected from various official public health databases, including the Japan Institute for Health Security, the Centers for Disease Control and Prevention, and other national surveillance systems. The study period extended from 2018 to July 2025, allowing a comparison of periods before, during, and after government restrictions.

Annual and monthly case counts were extracted and used to calculate incidence rates per 100,000 population.

For countries lacking direct monthly data, weekly reports were aggregated. Age-specific incidence rates and case proportions were analyzed to identify demographic trends, particularly among adolescents and infants. Geographic distribution was examined at subnational levels using incidence-mapping tools.

Temporal changes were evaluated using an analysis of three distinct phases: pre-COVID-19 (2018-2019), pandemic restriction phase (2020-2022), and post-restriction phase (2023-2025). Statistical comparisons were conducted using nonparametric tests due to nonnormal data distributions.

Researchers used time-series analysis with segmented regression models to evaluate how changes in pandemic measures affected infection trends from 2023 and measured these changes using rate ratios. Ethical approval was not required, as all data were anonymous and publicly available.

Japan’s 2025 Outbreak and Age Shift Findings

Across all five countries, pertussis cases declined sharply during the COVID-19 pandemic (2020-2022), showing the impact of social distancing, masking, and reduced mobility, but this suppression was temporary. When restrictions were lifted, resurgence occurred, with all countries showing marked increases in incidence during 2023-2025.

Statistical analysis showed that pertussis incidence increased significantly after the pandemic preventive measures phase in all five countries, although the study was descriptive and did not prove a single cause for the rebound.

Australia, New Zealand, China, and the United States recorded their highest pertussis outbreaks in 2024, with Australia reporting the highest incidence at more than 200 cases per 100,000.

Japan had a delayed outbreak compared to other countries; whereas other countries began to decline after their peaks, Japan saw a dramatic increase in the number of cases (60,826 by July 31, 2025, based on a partial-year count), with more than ten times the number reported in 2024.

This delayed outbreak may reflect a gradual accumulation of susceptible individuals rather than an immediate rebound, although the authors noted that differences in surveillance systems, vaccination coverage, and other factors may also have contributed.

The distribution of age by disease category changed dramatically from past records. In the past, infants had the highest incidence rates of disease. However, with recent epidemics, there seems to be an increased incidence of disease among teens and school-aged children. In Japan in 2025, 10-19-year-olds accounted for more than 50% of all cases, and incidence rates reached over 270/100,000 population.

The emerging trend shows that immunity from childhood vaccinations is beginning to wane and that there are obstacles to booster vaccine uptake.

Geographically, distinct patterns emerged. In Japan and New Zealand, higher incidence rates were observed in non-metropolitan regions, suggesting potential links to population structure, healthcare access, or differences in vaccination coverage.

Conversely, Australia’s outbreak was concentrated in densely populated states, while the United States showed mixed patterns across regions.

Vaccination coverage remained high for primary childhood immunization across all countries, often exceeding 90%. However, booster vaccination strategies varied significantly. Countries with routine adolescent boosters showed different outbreak patterns, whereas Japan experienced a more pronounced surge among adolescents.

Because the vaccination data were ecological, however, the study could not confirm individual-level protection gaps or prove that booster policy differences directly caused the observed outbreaks.

Mortality remained relatively low but concerning, particularly among vulnerable populations. Infants continued to face severe outcomes, and deaths were also reported in older age groups, indicating that pertussis remains a risk across the lifespan.

Booster Vaccination and Public Health Implications

The resurgence of pertussis after the COVID-19 pandemic shows the unintended consequences of disrupted immunity and changing public health dynamics. While most countries experienced an early resurgence, Japan’s unique experience highlights significant concerns associated with the absence of government-funded routine pertussis boosters for adolescents and preschool children. Additionally, this change in the age of individuals contracting pertussis has serious implications for ongoing transmission and infant protection.

The findings support considering routine booster vaccines and vaccination during pregnancy as potential strategies to reduce future risk, rather than proving that these measures alone will prevent future outbreaks. These findings show the need for adaptive, evidence-based public health policies to address evolving infectious disease threats in a post-pandemic world.