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J Infect Dis
. 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
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.
. 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
- PMID: 39052720
- DOI: 10.1093/infdis/jiad539
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.