Impact of Waning Immunity on Measles Outbreaks and Vaccination Strategies in Nosocomial Infection

JunyoungPark

Konkuk University

"Impact of Waning Immunity on Measles Outbreaks and Vaccination Strategies in Nosocomial Infection"

Secondary vaccine failure(SVF) following the second dose of measles-mumps-rubella(MMR) vaccine has resulted in low seroprevalence among healthcare workers(HCWs) in their 20s in the Republic of Korea. During the 2019 measles outbreak, 73% of confirmed cases in a hospital were seropositive yet still infected, highlighting that the presence of antibodies does not guarantee full protection. This study evaluates the impact of waning immunity on future measles outbreaks and develops vaccination strategies to control the nosocomial transmission. We developed a SEIR model incorporating three immunity states; Protected, Partially protected, and Seronegative, and integrated hospital seroprevalence and age structure. Using the stochastic Gillespie algorithm, we simulated the 2019 outbreak and predicted future scenarios. Our analysis revealed that the transmission rate among seronegative individuals was approximately 2.66 times higher than that of partially protected individuals. In long-term projections, vaccination only for new HCWs reduced confirmed cases by 41–51% compared to no vaccination. In contrast, vaccination for all HCWs suppressed outbreaks for approximately one year by reducing the effective reproduction number below 1. However, infections among partially protected individuals caused the overall outbreak size to increase over time. While current guidelines for third dose of MMR focus on seronegative individuals, our study provides mathematical evidence that booster shots for all HCWs are a more effective strategy than targeting only seronegative individuals in nosocomial environments.
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