Uptake and predictors of newborn respiratory syncytial virus (RSV) immunisation with nirsevimab in Ireland’s national pilot programme: a cross-sectional study

Abstract

Objectives

To assess uptake of nirsevimab, a long-acting monoclonal antibody for respiratory syncytial virus (RSV) prevention, during the first season of Ireland’s Pathfinder pilot universal newborn immunisation programme and to identify socio-demographic and perinatal predictors of uptake.

Design

Cross-sectional analysis of routinely collected programme data.

Setting

Ireland’s Mid-West region, served by University Maternity Hospital Limerick, the sole maternity and neonatal hospital for the region.

Participants

Infants born 1 September 2024 to 28 February 2025.

Outcome measure

Uptake of nirsevimab before hospital discharge.

Results

Overall uptake was 89.4% (1600/1790) and did not vary by month (p=0.119); it was similar by sex (male 89.5%, female 89.2%; p=0.838). Preterm infants had higher uptake than term (96.9% vs 88.7%; p=0.001), and those admitted to the neonatal unit also had higher uptake (93.0% vs 88.4%; p=0.009). In adjusted analyses, maternal age (adjusted OR (aOR) 1.06 per year, 95% CI 1.03 to 1.09, p<0.001) and preterm birth (aOR 3.08 (95% CI 1.14 to 8.37), p=0.027) were associated with uptake. Uptake varied by maternal ethnicity: 91.5% in white Irish, 53.6% in Irish Traveller (aOR 0.13 (95% CI 0.08 to 0.23)), 79.7% in other white background (aOR 0.39 (95% CI 0.24 to 0.61)), 90.0% in black or black Irish, 98.3% in Asian or Asian Irish and 84.2% in other/mixed or prefer not to say. Although uptake among white Irish was high, they accounted for the largest absolute number of infants who did not receive nirsevimab, reflecting their predominance in the birth cohort.

Conclusions

During the first season of Ireland’s Pathfinder RSV pilot programme in the Mid-West region, nearly 90% of newborns received nirsevimab before discharge. Uptake was consistently high across months, indicating effective implementation but lower among infants of Irish Traveller and other white background mothers, highlighting the need for targeted, culturally adaptable equity strategies within a high-uptake programme. These findings may inform national and international policies and offer practical lessons for universal RSV immunisation.

STRENGTHS AND LIMITATIONS OF THIS STUDY.

• Data were extracted directly from programme collection forms, ensuring contemporaneous and complete recording of immunisation status.

• Uptake was examined across multiple socio-demographic and perinatal factors, allowing assessment of equity in coverage.

• While the population served is one of the six designated health regions in Ireland, observations from a single regional maternity hospital as the provider may limit generalisability to other parts of Ireland.

• Some minority ethnic groups had small sample sizes, although differences observed were generally consistent with previous literature.

Introduction

Respiratory syncytial virus (RSV) is a major global cause of acute lower respiratory tract infection (LRTI) in young children, responsible for an estimated 33 million episodes annually, 3.6 million hospital admissions and approximately 100 000 deaths in children under 5 years.1,3 The burden is highest among infants and in low- and middle-income countries, where more than 90% of RSV-associated deaths occur.^{2 4 5} In high-income settings, RSV remains a leading cause of infant hospitalisation, with seasonal surges that begin by increasing presentations in primary care, escalate demand in emergency departments and culminate in pressures on paediatric and critical care services.^{6 7}

Clinical presentation varies by age, from sepsis-like illness and apnoea in neonates to bronchiolitis and pneumonia in older infants, with potential progression to hypoxaemia, respiratory failure or death.¹ Although prematurity, chronic cardiopulmonary disease and neuromuscular disorders confer increased risk of severe RSV, the majority of hospitalisations occur in previously healthy infants.^{8 9} Early vaccine efforts in the 1960s using a formalin-inactivated RSV vaccine were halted after recipients developed vaccine-associated enhanced disease.¹⁰ Subsequent advances enabled maternal vaccines and long-acting monoclonal antibodies.^{11 12} Among these, nirsevimab is a recombinant human monoclonal antibody engineered for extended half-life, and is administered as a single intramuscular dose for passive protection against RSV infection.¹³ The MELODY trial demonstrated that nirsevimab reduced medically attended RSV-LRTI by 74.5% in healthy late-preterm and term infants, through 150 days post-randomisation.¹⁴ The HARMONIE trial demonstrated reductions in RSV-related hospitalisations by 83.2% and very severe disease by 75.7%¹⁵ with protection to 180 days.¹⁶

Emerging real-world evidence from the 2023 to 2024 RSV season includes reports of infant nirsevimab uptake ranging from 51.2% to 90.1%,¹⁷ with estimates showing approximately 75–85% reductions in RSV-related hospitalisations and severe outcomes.^{18 19} Prior to nirsevimab, RSV prophylaxis was limited to a costly monthly palivizumab for a narrow high-risk group.²⁰ The simplicity of a single-dose supports population-level impact.

In Ireland, the Health Service Executive (HSE) launched the RSV 1.0 Pathfinder pilot for the 2024–2025 winter season, providing free, state-funded passive immunisation with nirsevimab to all infants born between 1 September 2024 and 28 February 2025 before discharge from the maternity unit, administered by midwives.²¹ During this period, among infants eligible for the programme (ie, those born between 1 September 2024 and 28 February 2025), national uptake of infant nirsevimab immunisation reached 83% and RSV surveillance data showed a 65% reduction in notified cases, a 57% reduction in emergency department presentations, a 76% reduction in hospital admissions and a 65% reduction in intensive care admissions compared with the 2023–2024 season.²²

Evaluating uptake of nirsevimab is essential to understand the feasibility of delivering universal infant RSV immunisation, to identify socio-demographic and perinatal factors associated with coverage and to inform strategies for equitable implementation. Despite high national uptake, little is known about variation at a regional level or the characteristics of newborns who received immunisation and those who did not. This study therefore examines nirsevimab uptake and its predictors among newborns during the 2024–2025 season in Ireland.

Methods

Study design

This was a cross-sectional analysis of routinely collected programme data.

Research Ethics Committee approval was not required based on the exemption clause for the de-identified notifiable disease data analysis approved by the HSE in Ireland, foundational on the Infectious Diseases Regulations of 1981 (amended in 2024 as number 528). Additional information is available at https://www.hpsc.ie/notifiablediseases/howwehandleyourdata/

Study setting

University Maternity Hospital Limerick (UMHL) is the sole stand-alone maternity and neonatal hospital serving the Mid-West of Ireland, with approximately 3900 deliveries annually and serves an area comprising the counties of Limerick, Clare and North Tipperary, corresponding to a mixed urban–rural catchment within a regional population of about 413 000. The population is predominantly white Irish (~79.5%), with smaller proportions from Irish Traveller (~0.9%) and other ethnic or cultural background groups (other white, black or black Irish, Asian or Asian Irish and other/mixed or prefer not to say), based on self-identified ethnicity in the most recent census (2022).²³

Study population

The analytical cohort comprised all liveborn newborn infants at UMHL who were actually offered nirsevimab under the national pilot programme. This included all births from 1 September 2024 to 28 February 2025, plus a small number born outside this window who nonetheless received the intervention (eg, August 2024 preterm newborns discharged after programme start, or early March 2025 births).

Newborns who were not offered immunisation because they died before an offer could be made, were transferred to another hospital before an offer, or remained inpatients beyond the pilot period (eg, very preterm newborns not yet discharged), and thus had no opportunity to be offered nirsevimab during the pilot, were excluded. These groups cannot be enumerated from programme data alone, as linkage with other hospital sources would be required and is outside the scope of this study.

Data sources and variables

Data were extracted from the HSE RSV Nirsevimab Data Collection Form—Newborn.²⁴ These forms were completed by clinical staff at the time of nirsevimab offer. From Section 1: Infant’s details, variables included sex, date of birth, gestational age, birth weight and neonatal unit admission. From Section 2: Mother’s details, variables included mother’s date of birth and ethnic or cultural background (self-reported). From Section 3: Administration details, we recorded whether nirsevimab was administered.

Statistical analysis

Infant sex was classified as male or female. Day of week of birth was coded from the infant’s date of birth and analysed as a categorical variable. A binary variable (public holiday birth) was derived from the infant’s date of birth to indicate births occurring on designated public holidays during the study period (October Bank Holiday, Christmas Day, St Stephen’s Day, New Year’s Day and St Brigid’s Day). Month of birth was also coded from the date of birth and analysed as a categorical variable. Maternal age at delivery was derived from mother’s and infant’s dates of birth, and examined both as a continuous variable (years; median and IQR) and in the following categories: (<20, 20–29, 30–39, ≥40 years). Gestational age was analysed as a continuous variable (weeks; median and IQR) and dichotomised as preterm (<37 completed weeks) versus ≥37 weeks. Birth weight was summarised as a continuous variable (kg; median and IQR) and dichotomised as low birth weight (<2.5 kg) versus ≥2.5 kg. Neonatal unit admission was recorded as yes or no. Maternal ethnic or cultural background was analysed in the categories: white Irish, Irish Traveller, other white background, black or black Irish, Asian or Asian Irish and other/mixed or prefer not to say. We included maternal ethnic or cultural background to examine equity in uptake. Ethnicity is treated as a social construct and is used here solely to detect potential disparities in access or acceptance of nirsevimab, not to infer biological causation.²⁵ While possibly relevant, as the Pathfinder national data compilation forms did not include maternal education/socioeconomic classification/home address-linked deprivation indices, such variables were not analysed as part of this study.

Uptake was calculated as the percentage of newborn infants who received nirsevimab before hospital discharge, based on an individual-level binary outcome (received: yes/no). Descriptive statistics compared infants who did and did not receive nirsevimab. Continuous variables were summarised using medians and IQRs and compared using the Mann-Whitney U test. Categorical variables were summarised as frequencies and row percentages, and compared using χ² or Fisher’s exact tests, as appropriate.

Multivariable logistic regression was used to identify independent predictors of nirsevimab uptake. Variables considered in the model were infant sex, month of birth, maternal age, gestational age, neonatal unit admission and maternal ethnicity. Neonatal unit admission was included because it represents a key service-level factor that may influence the opportunity for, or timing of, immunisation before discharge. In the multivariable logistic regression, gestational age was retained because preterm birth (<37 weeks) is a recognised risk factor for RSV severe infection.²⁰ In this cohort, gestational age and birth weight were correlated (Pearson r=0.63), and previous work has also modelled only one of them²⁶; thus, birth weight was excluded for parsimony. A prespecified season-restricted sensitivity analysis was conducted, limited to infants born between 1 September 2024 and 28 February 2025, using the same covariates and model specification as the primary analysis to assess robustness of findings. Model calibration was assessed using the Hosmer-Lemeshow goodness-of-fit test. Results are presented as ORs and adjusted ORs (aOR) with 95% CIs. Multicollinearity was assessed using variance inflation factors. Logistic regressions used robust SEs.

Statistical analyses were performed using Stata/BE V.17.0 (StataCorp LLC, College Station, Texas, USA). All statistical tests were two-tailed, and p values<0.05 were considered statistically significant. To protect confidentiality, cell counts of five or fewer and any values that would enable back-calculation were suppressed in all tables and figures, in accordance with the HSE Data Protection Statement.²⁷ This manuscript was prepared in accordance with the STROBE (Strengthening the Reporting of Observational Studies in Epidemiology) guidelines.

Results

A total of 1790 infants were included, of whom 1600 (89.4%) received nirsevimab. Data completeness was 100% for all variables. Figure 1 shows the distribution of days from birth to nirsevimab administration; 80.9% of infants received nirsevimab within 4 days of birth, and among those immunised on or after day 12, ≥90% had been admitted to the neonatal unit. The median gestational age was 39+0 weeks (IQR 38+0–39+6) and the median birth weight 3.39 kg (IQR 3.06–3.70). The cohort included 917 males (51.2%), and 398 newborns (22.2%) were admitted to the neonatal unit. This proportion reflects local clinical admission practices and thresholds. Mothers had a median age of 33.4 years (IQR 29.4–36.6). Baseline infant and maternal characteristics are shown in table 1 and online supplemental eTable 1.

Figure 1. Distribution of days between birth and nirsevimab administration.

Table 1. Characteristics of infants by nirsevimab uptake.

Characteristic	Total (N=1790, 100%)	Nirsevimab yes (n=1600, 89.4%)	Nirsevimab no (n=190, 10.6%)	P value
Sex				0.838
Male	917 (51.2)	821 (89.5)	96 (10.5)
Female	873 (48.8)	779 (89.2)	94 (10.8)
Maternal age (years)	Median (IQR): 33.4 (29.4–36.6)	33.6 (29.8–36.8)	31.3 (26.3–35.6)	<0.001*
<20 years	26 (1.5)	18 (69.2)	8 (30.8)
20–29 years	472 (26.3)	396 (83.9)	76 (16.1)
30–39 years	1148 (64.1)	1052 (91.6)	96 (8.4)
≥40 years	144 (8.0)	134 (93.1)	10 (6.9)
	P for bands			<0.001*
Gestational age (weeks)	Median (IQR): 39+0 (38+0–39+6)	39+0 (38+0–39+6)	39+1 (38+3–40+0)	0.020*
<37 weeks	—	96.9	—
≥37 weeks	—	88.7	—
	P for bands			0.001*
Birth weight (kg)	Median (IQR): 3.39 (3.06–3.70)	3.38 (3.05–3.71)	3.40 (3.13–3.66)	0.506
<2.5 kg	127 (7.1)	118 (92.9)	9 (7.1)
≥2.5 kg	1663 (92.9)	1482 (89.1)	181 (10.9)
	P for bands			0.181
Neonatal unit admission				0.009*
Yes	398 (22.2)	370 (93.0)	28 (7.0)
No	1392 (77.8)	1230 (88.4)	162 (11.6)
Mother’s ethnic or cultural background				<0.001*
White Irish	1280 (71.5)	1171 (91.5)	109 (8.5)
Irish Traveller	69 (3.9)	37 (53.6)	32 (46.4)
Other white background	148 (8.3)	118 (79.7)	30 (20.3)
Black or black Irish	—	90.0	—
Asian or Asian Irish	—	98.3	—
Other/mixed or prefer not to say	76 (4.2)	64 (84.2)	12 (15.8)
Month of birth				0.119
September 2024	280 (15.6)	248 (88.6)	32 (11.4)
October 2024	322 (17.9)	297 (92.2)	25 (7.8)
November 2024	287 (16.0)	252 (87.8)	35 (12.2)
December 2024	—	90.2	—
January 2025	303 (16.9)	270 (89.1)	33 (10.9)
February 2025	236 (13.1)	203 (86.0)	33 (14.0)
Month outside September to February (eg, August 2024 and March 2025)	—	97.8	—

IQR for continuous variables. Values are presented as n (%) unless otherwise stated. ‘—’ indicates suppression for confidentiality, applied where counts were ≤5 or where disclosure risk required additional suppression to prevent back-calculation.

^*P value<0.05.

Uptake of nirsevimab

Overall uptake was high and similar by sex (821/917 males, 89.5% vs 779/873 females, 89.2%; p=0.838). Uptake varied by maternal age, from 18/26 (69.2%) among newborns of mothers <20 years old, 396/472 (83.9%) among mothers aged 20–29 years to 1052/1148 (91.6%) for those aged 30–39 years and 134/144 (93.1%) for those aged ≥40 years (p<0.001). Infants admitted to the neonatal unit had higher uptake (370/398, 93.0%) than those not admitted (1230/1392, 88.4%; p=0.009). Infants born preterm (<37 weeks) had higher uptake (96.9%) than those born at term (≥37 weeks, 88.7%; p=0.001). Uptake did not differ significantly by birth weight when dichotomised (<2.5 kg: 118/127, 92.9% vs ≥2.5 kg: 1482/1663, 89.1%; p=0.181).

Uptake among infants varied markedly by maternal ethnic or cultural background (figure 2). Uptake was 1171/1280 (91.5%) among white Irish, 37/69 (53.6%) among Irish Travellers, 118/148 (79.7%) among other white background, 90.0% among black or black Irish, 98.3% among Asian or Asian Irish and 64/76 (84.2%) among other/mixed or prefer not to say; exact counts are suppressed for some groups where n≤5 or where suppression was required to prevent back-calculation. Uptake did not differ significantly by month of birth (figure 3; range 86.0–92.2%; p=0.119) or by day of the week of birth (range 86.6–90.9%; p=0.770). Uptake did not differ by public holiday birth (p=0.160).

Figure 2. Nirsevimab uptake by mother’s ethnic or cultural background. The dashed line marks overall uptake. Counts above bars are shown except where cell counts were ≤5 or where suppression was required to prevent back-calculation, in which case only percentages are displayed.

Figure 3. Percentage of newborn infants receiving nirsevimab before discharge by month of birth and gestational age. ‘Outside season’ refers to infants born in for example, August 2024 or March 2025 who received nirsevimab during the pilot period.

Predictors of uptake

In adjusted logistic regression (table 2), infant sex and month of birth were not significantly associated with uptake. Higher maternal age was associated with greater uptake (aOR 1.06 per year, 95% CI 1.03 to 1.09, p<0.001). Infants born <37 weeks had greater odds of immunisation compared with term infants (aOR 3.08, 95% CI 1.14 to 8.37, p=0.027).

Table 2. Logistic regression predictors of nirsevimab uptake.

Characteristic	n	Crude OR (95% CI)	P value	Adjusted OR (95% CI)	P value
Infant sex
Female (ref)	873	1.00		1.00
Male	917	1.03 (0.76 to 1.39)	0.838	1.07 (0.78 to 1.48)	0.670
Maternal age
<20	26	0.21 (0.09 to 0.48)	<0.001*	0.41 (0.12 to 1.41)	0.158
20–29	472	0.48 (0.34 to 0.66)	<0.001*	0.56 (0.39 to 0.78)	0.001*
30–39 (ref)	1148	1.00		1.00
≥40	144	1.22 (0.62 to 2.40)	0.560	1.14 (0.57 to 2.30)	0.713
per year (continuous)	—	1.08 (1.06 to 1.11)	<0.001*	1.06 (1.03 to 1.09)	<0.001*
Gestational age
≥37 weeks (ref)	—	1.00		1.00
<37 weeks	—	3.94 (1.60 to 9.73)	0.003*	3.08 (1.14 to 8.37)	0.027*
Admission to neonatal unit
No (ref)	1392	1.00		1.00
Yes	398	1.74 (1.15 to 2.64)	0.009*	1.56 (0.99 to 2.47)	0.056
Mother’s ethnic or cultural background
White Irish (ref)	1280	1.00		1.00
Irish Traveller	69	0.11 (0.06 to 0.18)	<0.001*	0.13 (0.08 to 0.23)	<0.001*
Other white background	148	0.37 (0.23 to 0.57)	<0.001*	0.39 (0.24 to 0.61)	<0.001*
Black or black Irish	—	0.84 (0.29 to 2.40)	0.741	0.79 (0.26 to 2.36)	0.666
Asian or Asian Irish	—	5.40 (1.70 to 17.18)	0.004*	5.93 (1.84 to 19.14)	0.003*
Other/mixed or prefer not to say	76	0.50 (0.26 to 0.95)	0.034	0.59 (0.29 to 1.17)	0.131
Month of birth
September 2024 (ref)	280	1.00		1.00
October 2024	322	1.53 (0.88 to 2.65)	0.128	1.46 (0.82 to 2.61)	0.201
November 2024	287	0.93 (0.56 to 1.55)	0.777	0.88 (0.51 to 1.53)	0.656
December 2024	—	1.19 (0.71 to 2.01)	0.513	1.25 (0.72 to 2.19)	0.431
January 2025	303	1.06 (0.63 to 1.77)	0.837	1.10 (0.63 to 1.92)	0.743
February 2025	236	0.79 (0.47 to 1.34)	0.384	0.76 (0.44 to 1.39)	0.319
Month outside September to February (eg, August 2024 and March 2025)	—	5.68 (0.76 to 42.6)	0.091	3.43 (0.42 to 29.27)	0.243

OR, CI, reference (ref). ‘—’ indicates suppression for confidentiality, applied where cell counts were ≤5 or where suppression was necessary to prevent back-calculation.

^*P value<0.05.

Disparities persisted by maternal ethnic or cultural background. Compared with white Irish, uptake was lower among Irish Travellers (aOR 0.13, 95% CI 0.08 to 0.23, p<0.001) and other white background (aOR 0.39, 95% CI 0.24 to 0.61, p<0.001), and higher among Asian or Asian Irish (aOR 5.93, 95% CI 1.84 to 19.14, p=0.003). No significant differences were observed for black or black Irish or other/mixed or prefer not to say groups.

In a prespecified season-restricted sensitivity analysis limited to infants born between 1 September 2024 and 28 February 2025 (online supplemental eTable 2), overall uptake was 89.2% (1556/1745), findings were materially unchanged. Associations with maternal age, preterm birth and ethnic background persisted. Uptake tended to be higher among infants admitted to the neonatal unit (aOR 1.56, 95% CI 0.99 to 2.47; p=0.056), indicating a consistent positive association that did not reach statistical significance and remained similar in the season-restricted model (aOR 1.53, 95% CI 0.97 to 2.41; p=0.069).

Model calibration was good (Hosmer-Lemeshow p=0.781 for the full model and p=0.986 in the season-restricted sensitivity analysis). All variance inflation factors were low (mean=1.30, maximum=1.78), indicating no evidence of multicollinearity in either the full or season-restricted models.

Discussion

Principal findings

In Ireland’s 2024–2025 pilot of universal newborn RSV immunisation, 89.4% of infants received nirsevimab before discharge from UMHL. Uptake was similar by infant sex and did not vary by month or day of week of birth; it was significantly higher in preterm than in term infants and increased with maternal age. Infants admitted to the neonatal unit had higher uptake, but this association was attenuated and no longer statistically significant after adjustment for other covariates. By mother’s ethnic or cultural background, uptake was high across most groups but significantly lower among infants of Irish Traveller and other white background mothers; it was similar to white Irish in black or black Irish and in the other/mixed or prefer not to say group, and was high in Asian or Asian Irish. Although uptake among white Irish was high, they accounted for the largest absolute number of infants who did not receive nirsevimab, reflecting their predominance in the birth cohort.

Comparison with other studies

The overall uptake achieved in this pilot is at the upper end of international experience. Recent reviews have documented uptake ranging from around 50% to 90% in the first year of nirsevimab roll-out.¹⁷ In the present study, uptake of 89.4% in the Mid-West exceeded the reported national average of 83% for the 2024–2025 season.²² The reasons for this difference are uncertain, and may reflect underlying population characteristics or local implementation factors. Nonetheless, the finding suggests that lessons from this setting may help inform efforts to optimise uptake across other regions. Additionally, national survey data show high parental acceptance of routine childhood vaccination in Ireland; however, the Mid-West’s before-discharge uptake of 89.4% still exceeds the national average of 83%, showing an effective multidisciplinary local implementation.²⁸

Implementation and programme performance

Moreover, uptake remained consistently high across all months of the pilot, with no evidence of a learning curve or decline over time. This contrasts with reports from other settings where uptake varied by month of birth,^{29 30} reflecting possible early implementation challenges or waning programme intensity. Taken together, these findings suggest that implementation in the Mid-West was robust and sustained throughout the season. The high and consistent uptake likely reflects the strength of programme implementation, which was achieved under substantial time pressure. The Pathfinder pilot was established within months of the National Immunisation Advisory Committee (NIAC) recommendation and operationalised nationally through coordinated efforts by the HSE, National Clinical Programme for Paediatrics and Neonatology and National Women and Infants Health Programme. The national RSV Pathfinder programme was implemented following the NIAC recommendation in April 2024 for universal newborn immunisation with nirsevimab. Led by the HSE, roll-out commenced by September 2024 across all maternity hospitals, offering a single dose before discharge. The programme was coordinated through the National Clinical Programme for Paediatrics and Neonatology and the National Women and Infants Health Programme, with national monitoring by the Health Protection Surveillance Centre (HPSC) and pharmacovigilance by the Health Products Regulatory Authority.²¹ This rapid, integrated roll-out may have contributed to the absence of an early learning curve and can provide an example of effective translation of policy into practice. Similarly, uptake did not vary by day-of-week of birth, suggesting equitable access and delivery across weekdays and weekends. This contrasts with the broader perinatal ‘weekend effect’, whereby weekend deliveries have been linked to higher rates of adverse maternal–neonatal outcomes.³¹ Uptake also did not differ between infants born on public holidays and those born on regular days. Midwives were central to programme delivery, consistent with their established role in maternal and newborn care, including medication administration and patient engagement in the postnatal period.³²

Most infants received nirsevimab within 3 days of birth, consistent with postnatal discharge practices in Ireland, where most mothers and infants are usually discharged within 2–3 days post partum.³³ Later administration predominantly involved infants who remained hospitalised in the neonatal unit, indicating that the timing of administration reflected clinical course rather than programme delay. This pattern demonstrates that administration before discharge is achievable within standard maternity care pathways.

Although a formal evaluation of implementation processes was beyond the scope of this study and would require separate investigation using qualitative or mixed-methods approaches,³⁴ the consistently high uptake and absence of temporal variation support the interpretation that early delivery was not subject to measurable disruption.

Equity and socio-demographic differences

In Ireland, maternity care is provided free at the point of use for all women ordinarily resident, and there are no private maternity hospitals,³⁵ removing financial and insurance-related barriers that are relevant in other health systems. Births outside hospital settings account for approximately 0.5% of all births in Ireland³⁶; planned home birth services in the Mid-West region have been suspended since 2022 and remain so at the time of writing.³⁷

Within this context, the pilot offered nirsevimab on a free and universal basis, and uptake appeared largely successful in reaching diverse socio-demographic groups. Uptake was significantly higher among infants of Asian or Asian Irish mothers, similarly high among those of white Irish and black or black Irish mothers, lower among those of other/mixed or prefer not to say mothers and significantly lower among those of other white background and Irish Traveller mothers. Comparable equity across Asian, white and black populations has also been reported in the USA when RSV prophylaxis was provided universally and at no cost, reinforcing the value of universal, free provision in mitigating disparities.³⁸ In another US study, however, substantially lower uptake was observed among infants identified as black and among those with public insurance, despite near-universal availability in clinical practice.²⁶ This suggests that structural barriers such as insurance coverage and practice-level variation, rather than ethnicity itself, play a key role in shaping uptake.

The ‘Other White background’ category, while heterogeneous, includes Ukrainian refugees displaced by the war in Ukraine that began in 2022, most of whom are women and children, who may face specific barriers to immunisation (eg, challenges related to recent displacement); however, this category is heterogeneous and lower uptake cannot be attributed to any single subgroup. This group may therefore require particular attention in programme planning to ensure equitable uptake.³⁹

In contrast with these generally high-uptake patterns, uptake was substantially lower among infants whose mothers identified as Irish Traveller, a recognised ethnic minority group in Ireland. This finding is consistent with longstanding evidence of health inequities in this community. The All Ireland Traveller Health Study reported that discrimination was strongly associated with poorer perceived access, quality of care and trust in providers,⁴⁰ while a qualitative study of Traveller women highlighted negative healthcare experiences, including lack of cultural respect and compassion.⁴¹ Taken together, these findings emphasise that while free and universal provision is essential, it is not sufficient on its own; culturally tailored strategies will be needed to ensure equitable uptake across all communities. Our observations underpin the relevance of the ‘4C model’ in the success of immunisation uptake, encompassing convenience, confidence, complacency and cultural acceptance to convert ‘immunisation availability’ to ‘immunisation acceptance’.⁴²

Maternal and perinatal factors

In the present study, older maternal age was associated with a modest but significant increase in uptake. This aligns with a large UK cohort analysis, which found that children of older mothers were somewhat more likely to be fully immunised in early childhood.⁴³ Another UK study of maternal RSV vaccination during pregnancy also observed higher uptake with older maternal age.⁴⁴ By contrast, a USA study of nirsevimab uptake did not identify maternal age as a predictor, suggesting that the association may be context-specific rather than universal.³⁸

Infants admitted to the neonatal unit had higher uptake, but this association was attenuated and not statistically significant after adjustment for other covariates, reflecting overlap with preterm birth and other factors. However, preterm birth itself remained significantly associated with uptake in both models, consistent with its recognised role as a risk factor for RSV and its prioritisation in clinical guidance.²⁰

Ireland’s decision to pilot universal infant immunisation for all infants born during the RSV season²¹ contrasts with Northern Ireland, where a maternal vaccination strategy has been implemented as part of the wider UK policy.^{44 45} This newborn-focused approach reflects the initial 2024–2025 pilot design, and the programme has since been extended from 2025 to 2026 to include a catch-up cohort of infants born between March and August who are entering their first RSV season and receive immunisation later in infancy outside the maternity setting.²²

While maternal immunisation offers protection via transplacental antibodies, uptake of maternal RSV vaccination has generally been lower than infant immunisation coverage.⁴⁴ A systematic review and meta-analysis reported population-level uptake of approximately 30% for maternal RSV vaccination in the USA, compared with substantially higher levels for infant nirsevimab programmes in Europe and the USA.¹⁷

A survey of pregnant women in Ireland found that 48.5% would be willing to accept an RSV vaccine in pregnancy, 45.8% were undecided and 5.3% would not accept it.⁴⁶ This indicates that, even if introduced, maternal RSV vaccination may encounter challenges in achieving high population-level uptake. Modelling analyses suggest that infant nirsevimab provides broader and more consistent protection than maternal immunisation, particularly for infants born outside of the RSV season and for the prevention of severe outcomes such as hospitalisation and intensive care admission.⁴⁷ In addition to cost-effectiveness, modelling evidence also indicates that infant immunisation with nirsevimab may also yield environmental co-benefits, with fewer RSV-related healthcare visits translating to lower greenhouse gas emissions.^{48 49} Findings from the present study, showing almost 90% uptake prior to discharge, support the feasibility and public health value of a strategy centred on universal infant immunisation.

Our study focused on uptake and its predictors, rather than outcomes. As mentioned earlier, national surveillance in Ireland has already demonstrated substantial reductions in RSV activity during the 2024–2025 season, coinciding with the introduction of universal newborn immunisation.²² At a national level, a surveillance-based analysis of RSV-associated hospitalisations in Ireland for the 2024–2025 season estimated that 437 infant hospitalisations were averted following the introduction of the universal newborn nirsevimab immunisation programme.⁵⁰ These observations are consistent with international evidence, such as in Catalonia, Spain, where high uptake of nirsevimab was associated with major reductions in RSV-related emergency attendances and hospitalisations among young infants.⁵¹ Although safety monitoring was an integral component of the national Pathfinder programme and evaluated nationally,²¹ this regional analysis focused specifically on uptake and its determinants. Future work is planned to examine outcomes in the Mid-West region, including RSV-related emergency department presentations, hospitalisations, paediatric high-dependency unit demand and the need for paediatric intensive care unit transfers.

Strengths and limitations

Strengths include the use of routinely collected programme data, ensuring contemporaneous and complete ascertainment of immunisation status and the ability to examine multiple socio-demographic and perinatal predictors. The single-centre design may limit generalisability, although UMHL serves a large mixed urban–rural catchment and provides a useful regional case study. Some minority ethnic groups had small sample sizes, limiting statistical power for those categories. However, the direction of observed differences, particularly the disparity among infants of Irish Traveller mothers, is consistent with the aforementioned published literature on health inequities in Ireland.^{40 41} As with all observational analyses, the possibility of residual confounding cannot be excluded, as not all relevant maternal, infant or service-level factors could be captured in the dataset. Analyses were restricted to the variables captured by the national newborn data form, which did not include some broader maternal or household characteristics that might also influence uptake. Nonetheless, the available data allowed assessment of key perinatal and socio-demographic predictors.

Conclusions

During the first season of Ireland’s Pathfinder pilot in the Mid-West region, nearly 90% of newborns received nirsevimab before discharge from the maternity hospital. Uptake was consistently high across months, which indicates effective implementation, but it was lower among infants of Irish Traveller and other white background mothers, highlighting the need for targeted and culturally aligned equity strategies within a high-coverage programme. These findings help to inform and optimise the ongoing national roll-out for the 2025–2026 season and beyond,²² inform international policy and offer practical lessons for universal RSV immunisation, including the future integration of additional long-acting monoclonal antibodies as they become available.⁵²

Data availability statement

Data are available upon reasonable request.