Factors Associated With Nirsevimab Uptake in Healthy Newborns

We reviewed charts of all newborns sequentially discharged from our hospital system (4 hospitals, combined annual delivery volume of ∼10,000) from December 15, 2023, through February 15, 2024. Nirsevimab was first offered in our network on October 26, 2023. Although nirsevimab administration was intermittently restricted during the 2023–2024 RSV season, nirsevimab was available to all newborns on our well-newborn units during the selected period (regardless of maternal RSV vaccination status). We report descriptive statistics of newborns who did and did not receive nirsevimab and unadjusted and adjusted relative risk with 95% confidence intervals using Poisson multivariable regression with robust standard errors.^5,6  Although race is a social construct, we included race in the analysis because differences in nirsevimab receipt could potentially identify disparities. Our institutional review board determined this study exempt.

Of 1326 newborns, 57% received nirsevimab during the study period. Patient characteristics by site can be found in Supplemental Table 2. Factors significantly associated with nirsevimab receipt included public or other insurance (compared with private insurance); primary language other than English; being a first-time parent; receipt of ocular prophylaxis and hepatitis B vaccine (HBV) (Table 1). Newborns admitted to community hospital site 3 were more likely to receive nirsevimab compared with the tertiary care site. All infants who did not receive intramuscular (IM) vitamin K also did not get nirsevimab.

In the first season of nirsevimab availability in our health system, the overall nirsevimab receipt rate was well below those of IM vitamin K, HBV, and ocular prophylaxis.⁷ 

Parents who refused common newborn interventions (IM vitamin K, HBV, and ocular prophylaxis) were more likely to refuse nirsevimab. Families who spoke languages other the English had a higher acceptance of nirsevimab. Other studies have found that although Spanish-speaking families exhibit vaccine hesitancy, the sentiment was not associated with undervaccination.^8,9  It is possible that providers present information differently to Spanish-speaking families. Although we expected that parents with other children might be more accepting of nirsevimab (because of increased knowledge of RSV and increased RSV exposure risks), we found that first-time parents in our study were slightly more likely to accept nirsevimab for their newborn.

Maternal RSV immunization was not associated with nirsevimab receipt. During this first season of both nirsevimab and maternal RSV vaccine availability, there may have been confusion among clinicians about whether nirsevimab was needed if the mother received RSV immunization during the pregnancy. We found differences in nirsevimab refusal rates between sites in our health system, which may be due to patient population, census, staffing, or procedures. This warrants further exploration to identify best practices.

Our study is limited by our single 4-hospital system and the sample size. It is possible that maternal receipt of RSV vaccine outside of our electronic medical record was not captured. Because this was the first season of nirsevimab availability for healthy newborns and behaviors may have been influenced by shortages, it is possible that findings in upcoming years may change. Because of the nature of this study, we were unable to determine whether all families were offered nirsevimab or whether newborns received nirsevimab after discharge. For newborns of mothers who received the RSV vaccine during pregnancy, we were unable to ascertain vaccination timing and physician interpretation of newborn eligibility.

We propose the need for qualitative studies to better understand parental concerns, preferences, and knowledge gaps about nirsevimab. Additionally, larger multisite studies through existing pediatric research networks should be leveraged to help inform pediatricians and newborn hospitalists about risk factors associated with parental concerns and in the context of other refusals to help us be better prepared for future years of nirsevimab.