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. 2025 Aug 30:62:127483.
doi: 10.1016/j.vaccine.2025.127483. Epub 2025 Jul 13.

Effectiveness of 2023-2024 seasonal influenza vaccine against influenza-associated emergency department and urgent care encounters among pregnant and non-pregnant women of reproductive age

Emily L Reeves  1 , Kristin Dascomb  2 , Stephanie A Irving  3 , Nicola P Klein  4 , Sara Y Tartof  5 , Shaun J Grannis  6 , Toan C Ong  7 , Sarah W Ball  8 , Gabriela Vazquez-Benitez  9 , Tamara Sheffield  2 , Daniel Bride  2 , Julie Arndorfer  2 , Joshua Van Otterloo  2 , Allison L Naleway  3 , Padma Koppolu  3 , Ousseny Zerbo  4 , Karen B Jacobson  4 , Bruce H Fireman  4 , John R Hansen  4 , Lawrence Block  4 , S Bianca Salas  5 , Cassandra Bezi  5 , Lina S Sy  5 , Iris Anne C Reyes  5 , Brian E Dixon  10 , William F Fadel  10 , Colin Rogerson  6 , Tom Duszynski  11 , David Mayer  7 , Catia Chavez  7 , Michelle A Barron  7 , Zachary A Weber  8 , Duck-Hye Yang  8 , Angela Cheung  8 , Amanda B Payne  12 , Ruth Link-Gelles  13 , Katherine Adams  12 , Varsha Neelam  12 , Malini B DeSilva  9 , Karthik Natarajan  14 , Mark W Tenforde  12 , Jennifer DeCuir  13 , Sascha Ellington  12 , Samantha M Olson  12
Affiliations

Effectiveness of 2023-2024 seasonal influenza vaccine against influenza-associated emergency department and urgent care encounters among pregnant and non-pregnant women of reproductive age

Emily L Reeves et al. Vaccine. .

Abstract

Influenza vaccination is particularly important for pregnant women. Using a test-negative, case-control design, we estimated the effectiveness of 2023-2024 seasonal influenza vaccination against influenza-associated emergency department and urgent care (ED/UC) encounters among pregnant and non-pregnant women of reproductive age using data from seven healthcare systems. Eligible encounters were among individuals aged 18-49 years with documented female sex. Vaccine effectiveness (VE) was estimated by comparing the odds of vaccination among influenza-positive cases versus influenza-negative controls, adjusting for site, age, race/ethnicity, calendar time, and gestational age at encounter (in pregnant women). Among pregnant women (N = 3539), VE against influenza-associated ED/UC encounters was 46 % (95 % CI: 36-55) and did not differ by gestational age at vaccination. Among non-pregnant women (N = 57,709), VE against influenza-associated ED/UC encounters was 54 % (95 % CI: 51-56). Influenza vaccination during the 2023-2024 season was similarly effective in both pregnant and non-pregnant women and by timing of vaccine receipt during pregnancy.

Keywords: Influenza; Pregnancy; Vaccine effectiveness.

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Conflict of interest statement

Declaration of competing interest All authors have completed and submitted the International Committee of Medical Journal Editors form for disclosure of potential conflicts of interest. During the conduct of the study, all Kaiser Permanente Southern California Department of Research and Evaluation and Kaiser Permanente Northern California Division of Research-affiliated authors reported receiving contractual support from the Centers for Disease Control and Prevention (CDC) via payments made to their respective institutions. Additionally, all authors affiliated with HealthPartners Institute, Intermountain Health, Kaiser Permanente Center for Health Research, Regenstrief Institute, and University of Colorado Anschutz Medical Campus reported receiving contractual support from the CDC during the conduct of the study, via subcontracts from Westat, Inc. with payments made to their respective institutions. The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: NPK reports support from Sanofi Pasteur, Merck, Pfizer, Seqirus, GlaxoSmithKline, Moderna, and Aztrazeneca. SYT reports contracts from Pfizer. SJG reports contracts with National Institutes of Health (NIH) National Center for Advancing Translational Sciences and NIH National Institute of Mental Health. TCO received consulting fees from Regenstrief Institute and support for travel from Patient-Centered Outcomes Research Institute (PCORI) and Regenstrief Institute and has a current patent, PCT/US2018/047961. GVB reports support from Sanofi Pasteur and Abbvie. TS is a member of CDC Advisory Committee on Immunization Practices Influenza Vaccine Work Group, chair of Utah Adult Immunization Coalition – volunteer vaccine quality improvement and advocacy group and a member of Utah Department of Health and Human Services Scientific Advisory Committee on Vaccines. OZ reports a contract with the National Institute of Allergy and Infectious Diseases. KBJ reports contracts with the National Institutes for Health and Pfizer. SBS reports a contract with Pfizer. LSS reports contracts with GlaxoSmithKline, Moderna, and Dynavax. BED, WFF, and MBD report contracts with Vaccine Safety Datalink Project. CR reports a grant from Indiana University Health. MAB was a speaker bureau participant – Innoviva Specialty Therapeutics -Oct 2023. SMO reports travel support from the Gates Foundation. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Figures

Figure 1.
Figure 1.
Total influenza vaccinations and counts of influenza-positive ED/UC encounters during the 2023-2024 influenza season by week among A) pregnant women and B) non-pregnant women.
Figure 2.
Figure 2.
Influenza vaccine effectiveness for pregnant and non-pregnant women by influenza type, encounter setting, time since vaccination (in days), and gestational age at vaccination in pregnant women. 1VE (%) calculated as (1-adjusted odds ratio)*100 with 95% confidence intervals. Estimates were adjusted for age in years, calendar time in days, site, race/ethnicity, and gestational age at encounter (in pregnant women). 2Includes pre-pregnancy vaccination during the 2023-2024 influenza season. Abbreviation: IQR, interquartile range
See this image and copyright information in PMC

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