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. 2024 Jul 25;230(1):e80-e92.
doi: 10.1093/infdis/jiad539.

Effectiveness of Influenza Vaccination During Pregnancy Against Laboratory-Confirmed Seasonal Influenza Among Infants Under 6 Months of Age in Ontario, Canada

Deshayne B Fell  1   2   3 , Margaret Russell  4 , Stephen G Fung  2 , Sarah Swayze  3 , Hannah Chung  3 , Sarah A Buchan  3   5   6   7 , Weston Roda  8 , Christa Smolarchuk  9 , Kumanan Wilson  10   11   12 , Natasha S Crowcroft  13 , Kevin L Schwartz  3   5   6   14 , Jonathan B Gubbay  5   15   16   17 , Allison J McGeer  6   15   18 , Marek Smieja  19 , David C Richardson  20   21 , Kevin Katz  15   22   23 , George Zahariadis  24 , Aaron Campigotto  15   25 , Samira Mubareka  15   26 , J Dayre McNally  27   28 , Timothy Karnauchow  27   29 , Nathan Zelyas  30   31 , Lawrence W Svenson  9   32   33   34 , Jeffrey C Kwong  3   5   6   35   36
Affiliations

Effectiveness of Influenza Vaccination During Pregnancy Against Laboratory-Confirmed Seasonal Influenza Among Infants Under 6 Months of Age in Ontario, Canada

Deshayne B Fell et al. J Infect Dis. .

Abstract

Background: Randomized trials conducted in low- and middle-income settings demonstrated efficacy of influenza vaccination during pregnancy against influenza infection among infants <6 months of age. However, vaccine effectiveness (VE) estimates from settings with different population characteristics and influenza seasonality remain limited.

Methods: We conducted a test-negative study in Ontario, Canada. All influenza virus tests among infants <6 months from 2010 to 2019 were identified and linked with health databases to ascertain information on maternal-infant dyads. VE was estimated from the odds ratio for influenza vaccination during pregnancy among cases versus controls, computed using logistic regression with adjustment for potential confounders.

Results: Among 23 806 infants tested for influenza, 1783 (7.5%) were positive and 1708 (7.2%) were born to mothers vaccinated against influenza during pregnancy. VE against laboratory-confirmed infant influenza infection was 64% (95% confidence interval [CI], 50%-74%). VE was similar by trimester of vaccination (first/second, 66% [95% CI, 40%-80%]; third, 63% [95% CI, 46%-74%]), infant age at testing (0 to <2 months, 63% [95% CI, 46%-75%]; 2 to <6 months, 64% [95% CI, 36%-79%]), and gestational age at birth (≥37 weeks, 64% [95% CI, 50%-75%]; < 37 weeks, 61% [95% CI, 4%-86%]). VE against influenza hospitalization was 67% (95% CI, 50%-78%).

Conclusions: Influenza vaccination during pregnancy offers effective protection to infants <6 months, for whom vaccines are not currently available.

Keywords: effectiveness; influenza; pregnancy; vaccination.

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Conflict of interest statement

Potential conflicts of interest . During the conduct of this work, D. B. F. worked for the University of Ottawa and had academic appointments at the Children's Hospital of Eastern Ontario Research Institute and ICES; she is currently employed by Pfizer. K. W. is a cofounder and Chief Scientific Officer of CANImmunize, Inc; he served on the Independent Data Monitoring Committee for Medicago; and is a member of the Moderna Global Advisory Core Consultancy Group. All other authors report no potential conflicts. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed.

Figures

Figure 1.
Figure 1.
Study flow diagram. aUncertain probability of match between the delivery records of the mother and infant. Abbreviation: LMP, last menstrual period.
Figure 2.
Figure 2.
Bar graphs displaying the estimated date of conception (A), specimen collection date (B), and date of birth (C) of influenza positive cases and influenza negative controls, by month.
Figure 3.
Figure 3.
Estimated effectiveness of maternal influenza vaccination during pregnancy against laboratory-confirmed influenza among infants <6 months of age (additional data provided in Supplementary Table 5). aVaccine effectiveness was estimated as 1 minus the adjusted odd ratio, comparing the odds of maternal influenza vaccination during pregnancy among test-positive infant cases relative to test-negative infant controls. Odds ratios were adjusted for infant age at test, season of birth, prenatal care adequacy, neighborhood income, and influenza season (with the exception of the subgroup analysis by infant age at test, for which odds ratios were adjusted for season of birth, prenatal care adequacy, neighborhood income, and influenza season). bResults for first and second trimester vaccinations were combined due to small cell counts. cResults for 60 to <120 days and 120 to <180 days were combined due to small cell counts. dInfluenza vaccines in 2014–2015 and 2017–2018 were not considered well matched against circulating influenza strains (see Supplementary Table 4). eCase specimens were limited to those collected during an admission to a hospital ward or intensive care unit. Controls were infants who tested negative for influenza in any clinical setting. Abbreviation: CI, confidence interval.
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References

    1. National Advisory Committee on Immunization . Statement on seasonal influenza vaccine for 2011–2012: An Advisory Committee Statement (ACS) National Advisory Committee on Immunization (NACI). Can Commun Dis Rep 2011; 37:1–55. - PMC - PubMed
    1. Ortiz JR, Perut M, Dumolard L, et al. . A global review of national influenza immunization policies: analysis of the 2014 WHO/UNICEF joint reporting form on immunization. Vaccine 2016; 34:5400–5. - PMC - PubMed
    1. Kay AW, Blish CA. Immunogenicity and clinical efficacy of influenza vaccination in pregnancy. Front Immunol 2015; 6:289. - PMC - PubMed
    1. Abu-Raya B, Madhi SA, Omer SB, et al. . Global perspectives on immunization against SARS-CoV-2 during pregnancy and priorities for future research: an international consensus paper from the World Association of Infectious Diseases and Immunological Disorders. Front Immunol 2021; 12:808064. - PMC - PubMed
    1. Nair H, Brooks WA, Katz M, et al. . Global burden of respiratory infections due to seasonal influenza in young children: a systematic review and meta-analysis. Lancet 2011; 378:1917–30. - PubMed

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