The optimal strategy for seasonal influenza vaccination to prevent high-intensity level of influenza epidemics in Zhejiang, China: an integrated transmission-dynamic and health-economic modeling analysis.

BACKGROUND

Although Seasonal Influenza Vaccination (SIV) is a crucial preventive measure, achieving sufficient coverage to completely control influenza epidemics poses a significant challenge. This study aims to evaluate optimal strategies for SIV to prevent high-intensity level of influenza epidemics in Zhejiang Province, China. High-intensity outbreaks were defined as weekly incidence rates above 72.2 per 100,000.

METHODS

This study estimated the incidence of influenza from 2018 to 2023 in Zhejiang Province, China, using influenza weekly surveillance data. We developed a Susceptible-Vaccinated-Infectious-Recovered-Susceptible (SVIRS) model to simulate influenza transmission and used a decision tree to assess seven vaccination strategies aimed at preventing high-intensity influenza outbreaks. These strategies differed in vaccine coverage across the three age groups: 0-14 years, 15-59 years, and 60 + years, despite having the same overall vaccination coverage.

RESULTS

Between 2018 and 2020, influenza incidence in Zhejiang Province followed typical seasonal patterns. However, during the COVID-19 pandemic, these patterns became irregular, culminating in a high-intensity influenza season in 2022-2023. Model simulations indicated that increasing population-wide vaccination coverage to 36.17% could effectively prevent outbreaks from escalating to high-intensity levels. Among various allocation strategies for additional vaccines, targeting individuals aged 0-14 years and those aged 60 years and older was found to be the most effective. This approach reduced the peak weekly incidence rate from the observed 182.83 to a predicted 42.28 per 100,000, saved 23.45 CNY per capita, and yielded a health gain of 0.0102 quality-adjusted life days (QALDs) per person.

CONCLUSION

Achieving a population-wide vaccination coverage beyond 36.17% is projected to prevent high-intensity level of influenza epidemics. Targeting the 0-14 years and 60 + years age groups proves to be the most cost-effective strategy under constrained coverage conditions. These findings highlight the importance of age-prioritized vaccination policies to optimize resource allocation and mitigate the impact of influenza outbreaks, particularly in regions with limited healthcare capacity.