Tim Karnauchow (Canada)
Children's Hospital of Eastern Ontario Department of PediatricsAuthor Of 1 Presentation
EFFECTIVENESS OF INFLUENZA VACCINATION DURING PREGNANCY ON LABORATORY-CONFIRMED SEASONAL INFLUENZA AMONG INFANTS UNDER 6 MONTHS OF AGE IN ONTARIO
Abstract
Backgrounds:
Despite high-quality evidence from randomized clinical trials conducted in low-middle income countries showing efficacy of influenza vaccination during pregnancy against influenza infection among infants <6 months of age, assessments of effectiveness in settings with different influenza seasonality and across multiple seasons are limited.
Methods
We conducted a test-negative study using population-based Ontario laboratory data to identify all influenza virus tests (in any clinical setting) among infants <6 months of age during 9 influenza seasons (2010-11 to 2018-19). These data were linked with health administrative data to ascertain information on maternal-infant dyads, including whether women had been vaccinated against influenza during pregnancy. Vaccine effectiveness (VE) was estimated from the adjusted odds ratio for vaccination, computed using logistic regression with adjustment for maternal age, infant age at test, season of conception, prenatal care adequacy, neighbourhood income, and influenza season. Women who received influenza vaccination less than 14 days prior to obstetric delivery or received the previous season’s vaccine were treated as unvaccinated.
Results:
Among 23,806 infants <6 months of age who were tested for influenza virus, 1,783 (7.5%) tested positive. Overall, 2,168 (9.1%) of infants were born to women vaccinated against influenza during pregnancy; 1,708 (7.2%) remained when those vaccinated less than 14 days before delivery or with the previous season’s influenza vaccine were reclassified as unvaccinated. Across seasons, the adjusted effectiveness of influenza vaccination during pregnancy against laboratory-confirmed infant influenza infection prior to 6 months of age was 64% (95% confidence interval: 51% to 74%).
Conclusions/Learning Points:
Since infants <6 months are at high risk for serious influenza-related illness, but not eligible for influenza vaccination, immunization during pregnancy is an effective strategy for protecting young infants during their first influenza season.