392 - Factors associated with Newborn nirsevimab administration in Los Angeles County during the 2024 Respiratory Syncytial Virus season

Publication Number: 2381.392

Huan V. Dong, University of California Los Angeles, Los Angeles, CA, United States; Neema Pithia, University of California, Los Angeles David Geffen School of Medicine, Los Angeles, CA, United States; Megan Halbrook, university of california, los angeles, Los Angeles, CA, United States; Choiyuk Chiang, Los Angeles County, Los Angeles, CA, United States; Melanie Barr, n/a, Los Angeles, CA, United States; Sherry Yin, Los Angeles County Department of Public Health, Los Angeles, CA, United States; Adriana Diaz, Los Angeles County Department of Public Health, Los Angeles, CA, United States; James Beekley, Los Angeles County Department of Public Health, Los Angeles, CA, United States; Nava Yeganeh, LACDPH, Los Angeles, CA, United States

Background: Respiratory Syncytial Virus (RSV) is a common cause of respiratory tract infections and is associated with significant morbidity, particularly for pediatric patients under 5 years of age. Since 2023, the Advisory Committee on Immunization Practices (ACIP) has recommended that all infants born during RSV season should receive nirsevimab within the first week of life to protect them from severe RSV disease during their infancy.

Objective: Describe factors associated with real-world uptake of nirsevimab in a large, diverse jurisdiction.

Design/Methods: We used descriptive analysis to define the characteristics of infants born during RSV season (10/1/2024-2/28/2025) who received nirsevimab and/or hepatitis B vaccinations in Los Angeles County (LAC) using California Immunization Registry (CAIR) . Birth dose was defined as vaccine administration within 7 days of birth.

Results: Of the 39,688 infants with a record in CAIR, 29.5% received a dose of nirsevimab, but only 15.8% received it within 7 days of life. Overall, 10,919 (27.5%) infants received both nirsevimab and hepatitis B vaccine, with 13.6% receiving both within 7 days of life.
Fifty six percent of infants who received a birth dose of nirsevimab were Hispanic vs 47.7% those who received hepatitis B vaccine at birth. Eligibility for the Vaccines for Children (VFC) program was more common among nirsevimab recipients of birth dose than hepatitis B birth dose recipients (35.6% vs. 11.2%) [Table 1].
A higher proportion of Hispanic infants received both nirsevimab and hepatitis B vaccine compared to those who received hepatitis B vaccine alone (58.0% vs. 45.5%) [Figure 1A]. Of infants who received both, 51.6% lived in a zip code with a high social vulnerability index to infants who received only hepatitis B vaccine (39.8%) [Figure 1B].

Conclusion(s): During the 2024-25 RSV season in LAC, nearly 5 times as many infants received birth dose of hepatitis B vaccine than nirsevimab. Only half of infants received nirsevimab within one week of birth, leaving infants potentially susceptible during the time they are most vulnerable for serious outcomes.
This is one of the few studies evaluating the "real world" implementation of nirsevimab in a large, highly diverse population suggesting that although nirsevimab administration shortly after birth was low this season, infants in the VFC program, who self-identified as Hispanic, and were living in the most at-risk zip codes had higher administration.

Table 1. Demographics of neonatal nirsevimab and hepatitis B vaccine birth-doses in Los Angeles County during the 2024 RSV season (October 1, 2024 - February 28, 2025)
LACNirsevuptake_Table1.pdf*Other category is composite of those who self-reported Alaska Indian/Alaska Native, Native Hawaiian/Pacific Islander, Multi-race, and other background
**HPI = Healthy Places Index Quartiles
*** Vaccines For Children Program includes those enrolled with Eligible Medi-Cal/CHDP, Eligible uninsured, Eligible Native American/AK native, Eligible Uninsured (FQHC/RHC Only)


Figure 1A. Proportion of infants 0-5 months of age who received birth doses of Nirsevimab and Hepatitis vaccination or Hepatitis B vaccination alone per self-reported race and/or ethnicity in Los Angeles County during the 2024 RSV season (October 1, 2024 - February 28, 2025)
Other category is composite of those who self-reported Alaska Indian/Alaska Native, Native Hawaiian/Pacific Islander, Multi-race, and other background

Figure 1B. Proportion of infants 0-5 months of age who received birth doses of Nirsevimab and Hepatitis vaccination or Hepatitis B vaccination alone per Healthy Place Index Quartiles in Los Angeles County during the 2024 RSV season (October 1, 2024 - February 28, 2025)