Recently, a study on Respiratory Syncytial Virus (RSV) in China was published in The Lancet Global Health, conducted by a team led by Professor Li You from Nanjing Medical University and Associate Professor Wang Xin.
The research indicates significant variations in the duration of RSV seasons among provinces, yet similar patterns of RSV circulation within the same transmission area. This further underscores the feasibility of seasonal immunization and emphasizes that RSV prevention vaccination strategies can be tailored based on the seasonal characteristics of different regions.
Significant Disparities in Infection Season Duration
RSV is a major pathogen causing acute lower respiratory tract infections, imposing a heavy disease burden globally, especially in low- and middle-income countries. It spreads through direct contact and airborne transmission, with a contagiousness about 2.5 times that of rotavirus, affecting individuals of all age groups throughout the year. While primarily manifesting as acute respiratory infections, symptoms vary among individuals, with mild cases possibly being asymptomatic or presenting with upper respiratory symptoms, while severe cases may exhibit lower respiratory infection symptoms, potentially leading to fatalities.
Given RSV's high infectivity and pathogenicity, the World Health Organization initiated the RSV surveillance network in 2016, with over 20 countries currently participating.
At the 2024 National Conference on Vaccines and Health in China, Zhang Yan, a researcher at the National Institute for Viral Disease Control and Prevention, highlighted the significant purpose and implications of RSV monitoring. It enhances global understanding of RSV across different countries and regions, identifies RSV circulation seasons through respective investigations, clarifies RSV age distribution, identifies high-risk groups for severe RSV infections in individuals under 2 years old, and characterizes viral variations. This data supports scientific evidence for future RSV prevention and control measures, aids in vaccine development, monoclonal antibody research, or the introduction of existing vaccines and monoclonal antibodies from overseas.
To delve deeper into the transmission patterns of RSV in China, Professor Li You's team and Associate Professor Wang Xin's team conducted surveys across 21 provinces or regions, revealing notable differences in the duration of RSV infection seasons among Chinese provinces.
Different regions in China exhibit varying intensities of RSV activity in different months, grouped by suitability for seasonal RSV immunization (and the appropriate starting month) using the sliding interval method.
"In temperate regions, the prevalence of respiratory syncytial virus (RSV) typically lasts 2 to 5 months, with peaks usually occurring in winter. In contrast, in tropical regions, RSV persists longer than in temperate regions, with peaks often aligning with the rainy season. Additionally, the seasonal pattern of RSV is significantly influenced by geographical factors such as latitude and altitude, as well as temperature and humidity variations," stated Li You.
Specifically, among the surveyed regions, the median duration of RSV transmission was 4.6 months, with significant differences in seasonal duration between provinces - provinces closer to the Tropic of Cancer experienced longer durations.
Zhang Yan led a team to study the monitoring of RSV infections domestically and internationally. The research revealed that RSV peaks in China often occur in winter and spring, with patients under 2 years old accounting for as much as 65.64% of cases. Among patients under 2 years old, the highest incidence was observed in infants aged 6 months, followed by those aged 6 months to 1 year.
Prevention is the most effective measure.
"To effectively prevent respiratory infections, vaccines are the most crucial tool," stated Feng Zijian, Vice President and Secretary-General of the Chinese Preventive Medicine Association, in his opening remarks at a special session.
"Currently, there are two innovative preventive measures for RSV: nirsevimab and palivizumab," explained Li You. Palivizumab was approved by the US FDA in 1998 for preventing congenital heart or lung diseases in premature infants born before 35 weeks but has not been approved in China. It requires dosing adjustments based on the recipient's weight, with a high cost per dose and necessitating 5 injections to cover a typical RSV season, lasting 5 to 6 months. Nirsevimab, recently approved in China, is a preventive measure for RSV in all infants and is expected to be used starting this infection season. Nirsevimab requires only one injection with a relatively fixed dosage, providing around 6 months of protection for infants.
Feedback data from real-world studies currently show over 90% effectiveness in both the US and Europe. "The US CDC Immunization Advisory Committee recommends vaccinating infants under 8 months at the onset of the first RSV season," Li You mentioned.
However, regarding the detailed analysis of RSV seasonal patterns and geographical variations in China from their previous research papers, Li You noted that seasonal vaccination strategies may not be applicable to all regions in the country due to differences in latitude leading to varying durations of RSV prevalence.
For instance, provinces like Fujian, Guangdong, and Yunnan have RSV transmission periods exceeding 6 months, surpassing the protection provided by nirsevimab vaccines.
"For regions suitable for seasonal vaccination, we recommend starting vaccinations in autumn," suggested Li You, "We hope that through innovative preventive measures, we can reduce the risk of RSV infections in more infants."
Related paper information: https://doi.org/10.1016/S2214-109X(24)00090-1
