The epidemiology and burden of respiratory syncytial virus and influenza infections in hospitalized children under five years old in Zhejiang, China (2018-2023)

Shelan Liu ^1* Wanwan Sun ¹ Yijuan Chen ¹ GUO LEI ² An Zhu ³ An Tang ⁴ Ziping Miao ¹ YinLi Yu ⁵ Fen Yuan ⁶ Xiaofei Fu ⁷ Suyan Shi ⁸ Lan Wang ⁹ Shijian Li ¹⁰ Xuxiao Zhi ⁸ Chunlei Zhu ⁸ Lefei Zhou ¹¹ Li Rui ⁶ Pang Yue ⁶ Zhao Yu ¹ Jin-ren PAN ¹ Chaorong Ni ¹²

• ¹ Zhejiang Center for Disease Control and Prevention (Zhejiang CDC), Hangzhou, China
• ² Department of Ultrasound, The Second Affiliated Hospital and Yuying Children's Hospital of Wenzhou Medical University, Wenzhou, Zhejiang Province, China
• ³ Lishui Second People's Hospital, Lishui, Zhejiang, China
• ⁴ Zhoushan Municipal Center for Disease Control and Prevention, Zhoushan, Zhejiang Province, China
• ⁵ Tonglu First People's Hospital, Hangzhou, Jiangsu Province, China
• ⁶ Tonglu Maternal and Child Health Center, Hangzhou, China
• ⁷ Jiaxing Center for Disease Control and Prevention, Zhejiang, China
• ⁸ The Second People's Hospital of Tonglu County, Hangzhou, China
• ⁹ First Affiliated Hospital, School of Medicine, Zhejiang University, Hangzhou, Zhejiang Province, China
• ¹⁰ Department of Public Health, SUNY at Old Westbury, New York, American Samoa
• ¹¹ Department of Psychiatry, Lishui Second People's Hospital, Lishui, China
• ¹² Wenzhou Center for Disease Control and Prevention, Wenzhou, Zhejiang Province, China

Objective: Estimate changes in hospital-based respiratory syncytial virus (RSV) disease burden compare this burden with influenza among children younger than 5 years old in China's Zhejiang Province.We enrolled hospitalized children under 5 years old from eight hospitals in Zhejiang Province. Multiple testing methods were used to compare epidemiological characteristics, and multivariate logistic regression analyses were used to estimate the odds ratio (OR) and 95% confidence interval (CI) between the two groups.Results: In this study, of the 7,857 RSV and 2,571 influenza patients, the median age of the children was significantly lower for RSV infection than for influenza. Inpatients with RSV had longer hospitalization durations (mean: 5.66 days vs. 5.04 days; P < 0.001) and hospitalization costs (mean: 5,616.12 RMB vs. 5,352.99 RMB; P = 0.023) than those with influenza. RSV inpatients increased from 1,081 before the COVID-19 pandemic to 6,776 after the pandemic (P < 0.001), with 526.8% more hospitalizations than before the pandemic (P < 0.001). During 2020-2023, hospitalized children were older (16.86 months vs. 10.09 months; P< 0.001) and had a higher proportion of pneumonia (82% vs. 75% of hospitalized patients; P < 0.001) than during pre-pandemic seasons for children admitted due to RSV infection. However, the average RSV hospitalization cost was much lower after the pandemic (4,299.29 RMB vs. 5,697.51 RMB; P < 0.001). Compared with the prepandemic years (2018-2019), the influenza groups showed a similar trend; the number of inpatients increased during the 2020-2023 season (1,949 vs. 622, P < 0.001), with older ages (33.13 months vs. 27.42 months, P < 0.001), a lower proportion of pneumonia (38% vs. 45%, P < 0.001), and lower costs (3,631.03 RMB vs. 3,742.59 RMB, P< 0.001). RSV infection was related to a higher risk of hospitalization in all age groups, and the greatest risk was observed in the 6-12 month age group (OR = 23.1; 95% CI, 18.0-29.6).RSV is a significant contributor to disease burden in hospitalized children under 5 years old, outweighing influenza. A more effective prevention strategy for both infections in young children, especially vaccinations against RSV and influenza is urged.