Epidemiological characteristics and transmission dynamics of dengue in Ningbo City, China before, during, and after the COVID-19 pandemic interventions
- 1Ningbo Municipal Center for Disease Control and Prevention, Ningbo, Zhejiang, People’s Republic of China
- 2State Key Laboratory of Vaccines for Infectious Diseases, Xiang An Biomedicine Laboratory, School of Public Health, Xiamen University, Xiamen, China
- 3School of Public Health, Chengdu Medical College, Chengdu, Sichuan, China
Abstract
Background: Ningbo experienced a local dengue outbreak in 2018–2019, followed by the implementation and relaxation of COVID-19 pandemic interventions. Evidence has been limited on dengue epidemiology and the transmissibility across these periods. Methods: We analyzed routine dengue cases and mosquito surveillance data from 2017 to 2024, using descriptive analyses to assess the epidemiological characteristics, and a mathematical model was developed to estimate the basic reproduction number (R0). Results: A total of 266 dengue cases were reported, with no deaths. Before the pandemic interventions, 51.19% of cases were overseas-imported; no cases were reported during pandemic interventions, whereas 73.47% were domestically imported after pandemic interventions. The median age of cases was 38.50 years (IQR = 31.25-54.00), and 57.52% were unemployed, retired, or in commercial services. The onset-to-diagnosis interval shortened post-interventions (4.46 days vs. 2.67 days). Viral typing increased post-interventions (34.59% vs. 63.27%), with 83.70% of cases identified as dengue virus-1 infections. Dengue cases were reported across all districts, with higher proportions in Haishu (27.07%) and Yinzhou (24.44%). The incidence was 2.82 per 100,000 persons. Incidence did not differ significantly by sex, but was significantly higher among individuals 15–59 years and those aged ≥60years than among those aged ≤14 years (3.18 and 3.01 per 100,000 persons, respectively, vs. 0.45 per 100,000 persons). Incidence was highest in Haishu and Jiangbei (6.90 and 4.93 per 100,000 persons, respectively). A post-intervention incidence rebound was observed, although no statistically significant differences were observed in the ≤ 14 age group, Beilun District, Ninghai County and Xiangshan County. Aedes albopictus was the only vector species. The mean Breteau Index was 16.07 (SD: 8.04) and decreased across phases, and rebounded in Jiangbei, Zhenhai, and Haishu districts. The mean BI was higher in summer compared to other seasons (p < 0.05). Model fit was strong (R2 > 0.95). The median R0 was higher in the outbreak years (3.46, IQR = 2.98-3.95) than years without local transmission (0.00, IQR = 0.00-0.00; p < 0.001). Median R0 was 0.00 (IQR = 0.00-0.71) over 2017–2024 due to the absence of local cases in most years. Conclusions: Dengue remains non-endemic in Ningbo, and is driven primarily by imported infections rather than sustained local transmission. Despite a reduction in diagnostic delay and vector density, post-PHSM incidences rebounded, and district-level heterogeneity indicates ongoing outbreak potential. Sustained surveillance, rapid diagnosis and district-tailored vector control are critical to prevent re-establishment of local transmission. Author summary: We examined how dengue changed in Ningbo, a coastal Chinese city where the disease is not usually established. We compared the years before, during, and after the public health measures used to control the coronavirus pandemic. We reviewed health records and mosquito surveys to understand who became ill, where cases occurred, and how mosquito numbers changed. We also used a computer-based model to assess the potential for dengue to spread locally. Among 266 reported cases, no cases occurred during the strictest control period. After the measures were relaxed, dengue returned, mainly in people infected elsewhere in China. Local spread occurred during outbreaks in 2018 and 2019, but it did not continue from year to year. Cases and mosquito numbers varied considerably between districts and were generally higher during the summer. Although people were diagnosed more quickly and mosquito numbers decreased overall, dengue incidence increased again in some districts after the control measures ended. These findings show that a city can remain at risk even when dengue is not permanently established. For Ningbo and other port cities, prevention should combine rapid diagnosis, attention to travel-related infections, continued mosquito monitoring, and targeted control in higher-risk districts.
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BibTeX
@article{chu2026epidemiological,
title = {{Epidemiological characteristics and transmission dynamics of dengue in Ningbo City, China before, during, and after the COVID-19 pandemic interventions}},
author = {Yanru Chu and Yunkang Zhao and Buasiyamu Abudunaibi and Yao Wang and Yanwu Zhang and Song Lei and Yang Mao and Tianfeng He and Tianmu Chen and Yi Chen},
journal = {PLOS Neglected Tropical Diseases},
year = {2026},
month = oct,
doi = {10.1371/journal.pntd.0014813},
url = {https://journals.plos.org/plosntds/article?id=10.1371/journal.pntd.0014813},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Epidemiological characteristics and transmission dynamics of dengue in Ningbo City, China before, during, and after the COVID-19 pandemic interventions
AU - Yanru Chu
AU - Yunkang Zhao
AU - Buasiyamu Abudunaibi
AU - Yao Wang
AU - Yanwu Zhang
AU - Song Lei
AU - Yang Mao
AU - Tianfeng He
AU - Tianmu Chen
AU - Yi Chen
PY - 2026
DA - 2026/10/30
JO - PLOS Neglected Tropical Diseases
DO - 10.1371/journal.pntd.0014813
UR - https://journals.plos.org/plosntds/article?id=10.1371/journal.pntd.0014813
AB - Background: Ningbo experienced a local dengue outbreak in 2018–2019, followed by the implementation and relaxation of COVID-19 pandemic interventions. Evidence has been limited on dengue epidemiology and the transmissibility across these periods. Methods: We analyzed routine dengue cases and mosquito surveillance data from 2017 to 2024, using descriptive analyses to assess the epidemiological characteristics, and a mathematical model was developed to estimate the basic reproduction number (R0). Results: A total of 266 dengue cases were reported, with no deaths. Before the pandemic interventions, 51.19% of cases were overseas-imported; no cases were reported during pandemic interventions, whereas 73.47% were domestically imported after pandemic interventions. The median age of cases was 38.50 years (IQR = 31.25-54.00), and 57.52% were unemployed, retired, or in commercial services. The onset-to-diagnosis interval shortened post-interventions (4.46 days vs. 2.67 days). Viral typing increased post-interventions (34.59% vs. 63.27%), with 83.70% of cases identified as dengue virus-1 infections. Dengue cases were reported across all districts, with higher proportions in Haishu (27.07%) and Yinzhou (24.44%). The incidence was 2.82 per 100,000 persons. Incidence did not differ significantly by sex, but was significantly higher among individuals 15–59 years and those aged ≥60years than among those aged ≤14 years (3.18 and 3.01 per 100,000 persons, respectively, vs. 0.45 per 100,000 persons). Incidence was highest in Haishu and Jiangbei (6.90 and 4.93 per 100,000 persons, respectively). A post-intervention incidence rebound was observed, although no statistically significant differences were observed in the ≤ 14 age group, Beilun District, Ninghai County and Xiangshan County. Aedes albopictus was the only vector species. The mean Breteau Index was 16.07 (SD: 8.04) and decreased across phases, and rebounded in Jiangbei, Zhenhai, and Haishu districts. The mean BI was higher in summer compared to other seasons (p < 0.05). Model fit was strong (R2 > 0.95). The median R0 was higher in the outbreak years (3.46, IQR = 2.98-3.95) than years without local transmission (0.00, IQR = 0.00-0.00; p < 0.001). Median R0 was 0.00 (IQR = 0.00-0.71) over 2017–2024 due to the absence of local cases in most years. Conclusions: Dengue remains non-endemic in Ningbo, and is driven primarily by imported infections rather than sustained local transmission. Despite a reduction in diagnostic delay and vector density, post-PHSM incidences rebounded, and district-level heterogeneity indicates ongoing outbreak potential. Sustained surveillance, rapid diagnosis and district-tailored vector control are critical to prevent re-establishment of local transmission. Author summary: We examined how dengue changed in Ningbo, a coastal Chinese city where the disease is not usually established. We compared the years before, during, and after the public health measures used to control the coronavirus pandemic. We reviewed health records and mosquito surveys to understand who became ill, where cases occurred, and how mosquito numbers changed. We also used a computer-based model to assess the potential for dengue to spread locally. Among 266 reported cases, no cases occurred during the strictest control period. After the measures were relaxed, dengue returned, mainly in people infected elsewhere in China. Local spread occurred during outbreaks in 2018 and 2019, but it did not continue from year to year. Cases and mosquito numbers varied considerably between districts and were generally higher during the summer. Although people were diagnosed more quickly and mosquito numbers decreased overall, dengue incidence increased again in some districts after the control measures ended. These findings show that a city can remain at risk even when dengue is not permanently established. For Ningbo and other port cities, prevention should combine rapid diagnosis, attention to travel-related infections, continued mosquito monitoring, and targeted control in higher-risk districts.
SN - 1935-2735
ER -