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Background <p>Invasive meningococcal disease (IMD) is a severe but rare infection in Japan. Changes in population mobility before, during, and after the Coronavirus disease 2019 (COVID-19) pandemic may have influenced IMD trends; however, recent epidemiological patterns in Japan remain incompletely described.</p> Methods <p>National surveillance data from January 2017 to October 2025 were analyzed. Temporal, age-specific, and geographic patterns were evaluated across three phases: Phase 1 (2017–2019, pre-COVID-19), Phase 2 (2020–2022, pandemic period), and Phase 3 (2023–October 2025, post-pandemic period with relaxed preventive measures). The relationship between annual IMD case counts and inbound international travel was explored using Spearman’s rank correlation.</p> Results <p>A total of 288 IMD cases were identified. Annual case numbers decreased markedly from 48 in 2019 to 1 in 2021 and subsequently increased to 66 in 2024 and 68 by October 2025. Case counts were significantly lower in Phase 2 than in Phase 1 (<i>p</i> = 0.0003) and significantly higher in Phase 3 than in Phase 2 (<i>p</i> &lt; 0.0001). Older adults consistently accounted for the largest number of cases, and adolescents showed a clear rebound in Phase 3. Geographic patterns demonstrated substantial prefectural heterogeneity; Tokyo showed the largest proportional increase, whereas Osaka and the Kansai region did not show a corresponding increase. Importantly, no distinct short-term increase in IMD incidence was observed during the Osaka Expo 2025 period. IMD case counts and inbound international travel exhibited parallel temporal patterns over the study period (Spearman’s <i>ρ</i> = 1.000).</p> Conclusions <p>IMD incidence in Japan decreased during the COVID-19 pandemic and increased again following the relaxation of public health measures. The post-pandemic rebound occurred alongside recovery of social contact and population mobility, while most cases were domestically acquired, and no event-specific surge was detected during the Osaka Expo 2025 period. These findings suggest that multiple contextual factors, including societal reopening and travel-related dynamics, may have contributed to the observed trends; however, causal relationships cannot be determined from this ecological analysis.</p>

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Nationwide epidemiology of invasive meningococcal disease in Japan, 2017–2025: implications of post-COVID-19 mobility

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年4月20日

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  • Yuhao Chen,
  • Hirotake Mori,
  • Shuhei Yokoyama,
  • Tingwei Wang,
  • Wenke Xie,
  • Mai Suzuki,
  • Mahoko Ikeda,
  • Yoshiro Hadano,
  • Rapeephan Rattanawongnara Maude,
  • Toshio Naito

摘要

Background

Invasive meningococcal disease (IMD) is a severe but rare infection in Japan. Changes in population mobility before, during, and after the Coronavirus disease 2019 (COVID-19) pandemic may have influenced IMD trends; however, recent epidemiological patterns in Japan remain incompletely described.

Methods

National surveillance data from January 2017 to October 2025 were analyzed. Temporal, age-specific, and geographic patterns were evaluated across three phases: Phase 1 (2017–2019, pre-COVID-19), Phase 2 (2020–2022, pandemic period), and Phase 3 (2023–October 2025, post-pandemic period with relaxed preventive measures). The relationship between annual IMD case counts and inbound international travel was explored using Spearman’s rank correlation.

Results

A total of 288 IMD cases were identified. Annual case numbers decreased markedly from 48 in 2019 to 1 in 2021 and subsequently increased to 66 in 2024 and 68 by October 2025. Case counts were significantly lower in Phase 2 than in Phase 1 (p = 0.0003) and significantly higher in Phase 3 than in Phase 2 (p < 0.0001). Older adults consistently accounted for the largest number of cases, and adolescents showed a clear rebound in Phase 3. Geographic patterns demonstrated substantial prefectural heterogeneity; Tokyo showed the largest proportional increase, whereas Osaka and the Kansai region did not show a corresponding increase. Importantly, no distinct short-term increase in IMD incidence was observed during the Osaka Expo 2025 period. IMD case counts and inbound international travel exhibited parallel temporal patterns over the study period (Spearman’s ρ = 1.000).

Conclusions

IMD incidence in Japan decreased during the COVID-19 pandemic and increased again following the relaxation of public health measures. The post-pandemic rebound occurred alongside recovery of social contact and population mobility, while most cases were domestically acquired, and no event-specific surge was detected during the Osaka Expo 2025 period. These findings suggest that multiple contextual factors, including societal reopening and travel-related dynamics, may have contributed to the observed trends; however, causal relationships cannot be determined from this ecological analysis.