Daily Respiratory Research Analysis

BACKGROUND: In March, 2024, Argentina became the first country to implement a national maternal immunisation programme with bivalent respiratory syncytial virus (RSV) prefusion F vaccine (RSVpreF) as the primary strategy to prevent RSV disease among infants. We aimed to evaluate vaccine effectiveness against RSV-associated lower respiratory tract disease (LRTD) and severe LRTD leading to hospitalisation among infants during the first season after implementation. METHODS: A multicentre, retrospective, test-negative, case-control study was done during the 2024 RSV season in 12 hospitals across Argentina (BERNI study). We included infants aged 6 months or younger who were hospitalised with LRTD between April 1 and Sept 30, 2024, and tested for RSV using PCR or indirect immunofluorescence; cases were infants with any positive RSV test and controls were PCR-confirmed negative for RSV. Infants were considered born to an RSVpreF-vaccinated pregnant woman if RSVpreF was received between 32 FINDINGS: Of 633 infants hospitalised for LRTD between April 1 and Sept 30, 2024, 505 (286 cases and 219 controls) met full eligibility criteria for inclusion in the primary vaccine effectiveness analysis; 51 (18%) cases and 109 (50%) controls were born to individuals who received RSVpreF during pregnancy. Vaccine effectiveness against RSV-associated LRTD leading to infant hospitalisation was 78·6% (95% CI 62·1-87·9) from birth to age 3 months and 71·3% (53·3-82·3) from birth to age 6 months. Effectiveness against RSV-associated severe LRTD leading to hospitalisation was 76·9% (45·0-90·3) from birth to age 6 months. Three RSV-associated in-hospital deaths occurred, all among infants whose mothers did not receive RSVpreF during pregnancy. INTERPRETATION: These real-world estimates for the 2024 RSV season in Argentina show high RSVpreF effectiveness against RSV-associated LRTD and severe LRTD leading to hospitalisation from birth to age 3 months and sustained to age 6 months. FUNDING: Pfizer. TRANSLATION: For the Spanish translation of the abstract see Supplementary Materials section.

IMPORTANCE: Respiratory syncytial virus (RSV) is associated with hospitalization and death among older adults. Characterizing the safety and effectiveness of recently introduced vaccines against RSV is critical. OBJECTIVE: To assess the safety and effectiveness of vaccines against RSV and the major adverse events among patients aged 60 years or older during the 2023-2024 RSV season. DESIGN, SETTING, AND PARTICIPANTS: In this study using a data platform containing electronic health records for more than 270 million patients across the US, a test-negative case-control design was used to estimate vaccine effectiveness (VE), and a self-controlled case series of vaccine recipients was included to estimate vaccine-associated adverse events. Records from participants aged 60 years or older with acute respiratory infection (ARI) and testing for RSV between October 1, 2023, and April 30, 2024, were included in the VE study. For vaccine safety analysis, all participants aged 60 years or older who received the RSV vaccine from July 1, 2023, to June 30, 2024 were included. Data were analyzed from August 2024 to March 2025. MAIN OUTCOMES AND MEASURES: Cases were those patients who tested positive for RSV, and controls were those who tested negative for RSV. Patients were classified as vaccinated if the vaccine was received at least 14 days before testing. VE against RSV-associated ARI diagnosis, emergency department or urgent care visits, or hospitalizations was estimated using (1 - odds ratio) × 100%. Excess risks of immune thrombocytopenic purpura and Guillain-Barré syndrome diagnosis for 6 weeks after vaccine administration were calculated. RESULTS: Of 787 822 patients tested for RSV, 53 963 were positive (733 859 were controls); 1318 cases (2.4%) and 66 928 controls (9.1%) were vaccinated. Overall, VE was 75.1% (95% CI, 73.6%-76.4%) against ARI and was similar for age groups of 60 to 74 years and 75 years or older and against urgent care visits or hospitalizations. Immunocompromised patients had a VE from 67.0% (95% CI, 62.6%-70.9%) for patients aged 60 to 74 years to 73.1% (95% CI, 69.9%-76.0%) for those aged 75 years or older, and the lowest VE (ie, from 29.4% [95% CI, 3.5%-48.4%] for patients aged 60-74 years to 44.4% [95% CI, 1.0%-68.8%] for those aged ≥75 years) was for a subgroup of patients who received stem cell transplants. Among 4 746 518 vaccine recipients, no excess risk of immune thrombocytopenic purpura diagnosis was detected. An excess of 5.2 cases (RSVPreF3+AS01) or 18.2 cases (RSVPreF) of Guillain-Barré syndrome were diagnosed per 1 000 000 doses of RSV vaccine administered. CONCLUSIONS AND RELEVANCE: VE for the RSV protein subunit vaccine in this case-control study was similar to the VE in clinical trials. The VE for immunocompromised patients was mildly (overall) to moderately (for stem cell transplant recipients) diminished. Risk of immune thrombocytopenic purpura after vaccination was not elevated, but the risk of Guilain-Barré syndrome was statistically significantly elevated in patients who received the RSVPreF vaccine but not in those who received RSVPreF+AS01 vaccine, although the risk was small. These observations should inform clinicians' choices and patient instructions.

Maternal respiratory syncytial virus (RSV) vaccine and nirsevimab, a long-acting monoclonal antibody for infants aged 0-7 months and children aged 8-19 months who are at increased risk for severe RSV disease, became widely available for prevention of severe RSV disease among infants and young children during the 2024-25 RSV season. To evaluate the association between availability of these products and infant and child RSV-associated hospitalization rates, the rates among children aged <5 years were compared for the 2024-25 and 2018-20 RSV seasons using data from the RSV-Associated Hospitalization Surveillance Network (RSV-NET) and New Vaccine Surveillance Network (NVSN). Among infants aged 0-7 months (eligible for protection with maternal vaccination or nirsevimab), 2024-25 RSV-associated hospitalization rates were lower compared with 2018-20 pooled rates (estimated relative rate reductions of 43% [RSV-NET: 95% CI = 40%-46%] and 28% [NVSN: 95% CI = 18%-36%]). The largest estimated rate reduction was observed among infants aged 0-2 months (RSV-NET: 52%, 95% CI = 49%-56%; NVSN: 45%, 95% CI = 32%-57%) and during peak hospitalization periods (December-February). These findings support Advisory Committee on Immunization Practices' recommendations for maternal vaccination or nirsevimab to protect against severe RSV disease in infants and highlight the importance of implementing the recommendations to protect infants as early in the RSV season as possible, before peak transmission, and for infants born during the RSV season, within the first week of life, ideally during the birth hospitalization.