389 - Differing Geographic Uptake of Nirsevimab versus Routine Vaccines

Publication Number: 2378.389

Britanny Winckler, University of California, Irvine, School of Medicine, Orange, CA, United States; Mingfei Dong, CHOC Children's Hospital of Orange County, Los Angeles, CA, United States; Jasjit Singh, Rady Children's Hospital Orange County, Orange, CA, United States

Background: The 2023-2024 national nirsevimab immunization rate was 44%. Vaccine hesitancy is widespread. It is unknown if passive immunization uptake will follow similar hesitancy patterns in certain populations and neighborhoods.

Objective: Identify which areas have the highest rates of nirsevimab administration, compare them to the distribution of routine vaccination uptake, and evaluate underlying sociodemographic characteristics.

Design/Methods: This was a single-center (integrated health system, non-birthing hospital) retrospective study of patients who had received nirsevimab from Sept 2023 – June 2025. We excluded patients with an unspecified home address, extracted encounter data (e.g., demographics, address, and acuity) from the electronic medical record, and mapped patients to their home zip code tabulation area (ZCTA). Kindergarten up-to-date vaccination rates were obtained from the public health department and mapped to their home ZCTA to calculate an aggregate ZCTA vaccination rate. We calculated a normalized and annualized nirsevimab rate and performed spatial analysis to identify nonrandom geographic clusters of high disease rate and immunization administration. Socioeconomic and demographic characteristics from the Childhood Opportunity Index 3.0 (COI) were compared using Wilcoxon rank sum test.

Results: Nirsevimab was administered to 1,753 children. A few ZCTAs had high vaccination coverage and high nirsevimab administration but several areas had only high nirsevimab or only high vaccination coverage (Fig. 1). Spatial analysis revealed a significantly high cluster of nirsevimab administration in the southern part of the county (Fig. 2A). In contrast, a significantly low cluster of vaccination was identified in a central region (Fig. 2B). Population-level demographics showed low vaccination and high nirsevimab clusters both had significantly more people identifying as White and fewer as Asian (Table 1). COI was higher in low vaccination clusters. Direct comparison of low vaccination and high nirsevimab clusters showed no significant socioeconomic differences.

Conclusion(s): Our study demonstrated that nirsevimab distribution outside of birth hospitalization does not match patterns of routine vaccination uptake. Sociodemographic disparities in nirsevimab distribution and routine vaccination exist. However, population-level demographics showed similar populations were both more likely to be delayed on vaccinations and more likely to accept nirsevimab. Next steps include comparing these rates to administration during birth hospitalization, maternal RSV vaccination, and influenza vaccine distribution.

Figure 1. Kindergarten Vaccination Rates Compared to Nirsevimab Administration.
Vax and Nirs Fig 1.pdfDark purple (scattered ZCTAs in the southern section and the northeastern county) indicates concordance between high vaccination rates and high nirsevimab rates. Light purple (northwest) indicates concordance between low vaccination rates and low nirsevimab rates. Dark blue (southern and north central) indicates low vaccination rates but high nirsevimab rates. Dark pink (northern borders) indicates high vaccination rates but low nirsevimab rates.

Figure 2. Hotspot Analyses of RSV and Nirsevimab Rates
Vax and Nirs Fig 2.pdfA hotspot analysis utilizes the Getis-Ord Gi* test to identify areas with unexpectedly high or low rates compared to the sample and the locations around the identified geographical unit. A) Vaccination Hotspot. Statistically significantly lower than expected rates were seen in a few ZCTAs in the western central region. B) Nirsevimab Hotspot. In contrast, there was a significant cluster of high rates of nirsevimab administration in the southern region.

Table 1. Census Demographics and Disease and Immunization
Vax and Nirs Table 1.pdfRates by RSV and Nirsevimab Hotspots. Data were reported as mean (SD). Significance was set at p<0.05. Population-level sociodemographic disparities were noted in high clusters of nirsevimab administration as well as in low clusters of vaccination uptake. In contrast, direct comparison of the population-level characteristics between low vaccination clusters and high nirsevimab clusters showed similar populations.
*Rate was normalized per 1000 children and annualized.
+Nine ZCTAs had no kindergarten vaccination rate data available due to blinding given low student numbers. All nine were classified as not significant in the nirsevimab hotspot analysis.
SD = standard deviation. COI = Childhood Opportunity Index 3.0