RSV Immunization Linked to Drop in Infant Hospitalizations

LYON, France — National programs using nirsevimab or maternal vaccination against respiratory syncytial virus (RSV) are associated with large reductions in infant hospitalizations, but there is wide variation in how they are implemented between countries, particularly for children born preterm, show two European studies.

The research was presented at the Congress of the European Paediatric Academic Societies (CEPAS) 2026 on October 29. Jeroen Geurtsen, MSc, of Global Medical Vaccines at Sanofi B.V. in Amsterdam, Netherlands, pointed out that although long-acting monoclonal antibodies such as nirsevimab have been available since 2022, “European countries have implemented these in different ways.” He explained that in Spain, nirsevimab immunization was introduced for all infants in autumn 2023, followed by the same universal coverage in Netherlands from autumn 2025, although maternal vaccination had been available out of pocket from December 2023.

In September 2024, the UK introduced year-round maternal RSV vaccination, adding nirsevimab for high-risk infants and those born before 32 weeks’ gestation from September 2025. To examine the real-world public health impact of these programs, the researchers used routine hospital administrative data and, for some institutions, laboratory data to perform a retrospective, observational study of the three countries.

They included infants aged 24 months or younger who were hospitalized with lower respiratory tract infection (LRTI) or RSV-related LRTI, and looked at four consecutive RSV seasons between June 2022 and May 2026, with the epidemiologic year defined as June 1 to May 31. Specifically, they collected information on the infants’ 24-month pre-index medical history, index hospitalization details, and 30-day postdischarge healthcare utilization.

Geurtsen and colleagues showed that just under half of hospital admissions were in infants aged 0-6 months and a further one quarter occurred in those aged 7-12 months. The mean age at admission ranged from 7 to 9 months, and around three fifths of infants were male. The results showed that in Spain, the RSV prevention program was associated with a 66.9% average reduction in RSV-related LRTI hospitalizations among infants aged 0-12 months across three post-implementation seasons, rising to 75.7% in those aged 0-6 months vs 36.8% in those aged 7-12 months.

In the UK, the RSV prevention program was linked to a 32.5% average reduction in RSV-related LRTI hospitalizations among infants aged 0-12 months across two postimplementation seasons. A decrease of 39.8% was seen in infants aged 0-6 months vs 5.1% in those aged 7-12 months. In Netherlands, introduction of the RSV program was associated with a 46.4% decrease in RSV-related LRTI hospitalizations among infants aged 0-12 months over a single postimplementation season.

This included a 56.1% drop in infants aged 0-6 months vs 26.5% in those aged 7-12 months. ICU data from Spain and the UK indicated that ICU admissions in infants aged 0-12 months fell by 74.5% and 49.7%, respectively, although median ICU length of stay was largely unchanged. In a separate presentation, Sara Marie Nilsen, PhD, of the Department of Clinical and Molecular Medicine at Norwegian University of Science and Technology in Trondheim, Norway, presented a mapping of immunization strategies against RSV and influenza in children born preterm.

She told the audience that “preterm born children are at increased risk of respiratory tract infections requiring hospitalization,” with a 10-fold increased risk in extremely preterm children (those born before 28 weeks’ gestation). This increased risk “extends beyond infancy and into early childhood.” To examine how European countries are addressing this risk, she and her colleagues mapped immunization strategies across 11 countries participating in the European Union-funded IMPROVE PRETERM project: Denmark, Estonia, Finland, France, Germany, Norway, Poland, Portugal, Sweden, Switzerland, and the UK.

A structured questionnaire was completed and validated by national clinicians and vaccination experts, focusing on strategies for RSV and influenza in effect for the 2025-2026 season. For RSV immunization, the researchers found a mix of approaches between the countries. France, Finland, Germany, Portugal, Sweden, and Switzerland offered universal protection for all infants, while the remaining five countries had some form of restriction based on weeks of gestation.

In addition, Denmark, France, Poland, Switzerland, and the UK had a free national maternal vaccination program. In the other six countries, this was not part of a free national program. For a child’s second RSV season, only Switzerland had a specific strategy for children born before 32 weeks’ gestation; the remainder had no gestational age -based eligibility for immunization.

For influenza immunization, only Norway had gestational age specified as an eligibility criterion (before 32 weeks’ gestation). Finland, Estonia, Poland, Portugal, and Switzerland offered immunization to all children, while Denmark, France, Germany, Sweden, and the UK targeted high-risk groups without mentioning gestational age.

Nilsen concluded that there was “substantial variation in immunization strategies” across the countries studied for preterm children, and that “protection beyond infancy was limited, especially for RSV,” despite these children being at higher risk. “So we believe that there is still room to improve protection against RSV and influenza in children born preterm.” Session co-chair Jasna Petrić Duvnjak, MD, a pediatric pulmonologist at Poliklinika Pediatri in Split, Croatia, asked what Nilsen thought were the “main barriers to achieving equal protection across the European countries,” suggesting that they could be political, financial, or cultural.

Nilsen replied that “it’s a complex question with complex answers and you brought some candidates” to the discussion. She pointed out that their mapping showed that the strategies used in each country “are quite different and we don’t really know which one is the best, so maybe that’s also part of the picture.” Expanding on her thoughts, Petrić Duvnjak told Medscape Medical News that she was “surprised” by the range of immunization strategies pursued by the countries included in the study, as “we learn from the same knowledge, and we share our knowledge, we share our experience.” She added: “Why are we so different?

Why do we have so different schedules?” Petrić Duvnjak pointed out that immunization guidelines are available, which in theory should guarantee unified practice. She highlighted that “some cultures are reluctant over vaccination or they hesitate, and maybe don’t believe enough in vaccination,” but she said she believes the root cause of the differences is “mostly politics, because the decision-makers are not physicians, they are not clinicians, they are not the ones that are involved in caring for sick children.” The REACH study was funded by Sanofi and AstraZeneca.

IMPROVE PRETERM was funded by the European Union’s Horizon Europe Research and Innovation program. Geurtsen is an employee of Sanofi B.V. and holds Sanofi stock options. Other authors of the REACH study are employees of Sanofi and LOGEX.

Nilsen reported no relevant financial relationships. Disclosures for Petrić Duvnjak were not available at the time of publication.