CAN-AIM responded to two queries raised by the Public Health Agency of Canada (PHAC) forthe National Advisory Committee on Immunization (NACI) in 2019 concerning the safety and effectiveness of the influenza vaccine in two vulnerable populations. Our results were helpful to PHAC and NACI, especially in light of the COVID-19 pandemic, when influenza vaccinationhas become even more important than in the past. 

Safety and effectiveness of influenza vaccine during pregnancy

Low influenza vaccination rates during pregnancy continue despite efficacy in preventing influenza infection in infants. Healthcare providers may be hesitant to suggest the vaccine to pregnant women due to safety concerns. Though it is generally believed that the benefits of protecting pregnant women and their newborns from influenza complications outweigh the small risks of vaccination, updated evidence is needed to support these recommendations. This project aimed to determine if influenza vaccination during pregnancy is safe and effective for women and their newborn babies. We studied women from the 3D Cohort Study (Design,Develop, Discover), comprising 2,366 women recruited during the first trimester of pregnancy(8–14 weeks) in Quebec. Influenza vaccine during pregnancy was not clearly associated with all-cause hospitalizations in newborns, small birth weight, or being small for gestational age. Our estimates for spontaneous abortions were not conclusive due to relatively low precision. In sensitivity analyses related to the timing of vaccine exposure, we were unable to determine if risk differed according to trimester.Our study confirms low influenza vaccine uptake in pregnancy, suggesting the need to promote influenza vaccine uptake in this group. Our results can inform an updated recommendation for using the influenza vaccine during pregnancy and could improve vaccine uptake in this high-risk group. 

Comparativeness effectiveness of influenza vaccines in elderly persons

This project aimed to provide real-world evidence on the comparative effectiveness of influenza vaccines in seniors using MarketScan® databases. This retrospective cohort study compared the effectiveness of standard-dose (SD) trivalent, high-dose (HD) trivalent, SD quadrivalent, and adjuvanted trivalent influenza vaccines in cohorts of Medicare beneficiaries 65 years of age and older over six influenza seasons (2012/2013-2017/2018 seasons). We analyzed the data pooled from all six seasons and each season separately. In the pooled analysis across all seasons, HD trivalent was associated with a lower risk of influenza-related hospitalization versus SD trivalent or SD quadrivalent. HD trivalent was also associated with alower risk for pneumonia-related hospitalization than SD trivalent. Adjuvanted trivalent was associated with a higher risk for influenza-related outpatient visits than HD trivalent, SD trivalent, or SD quadrivalent. Risk estimates varied across seasons. Compared to the SD trivalent, subjects who received the HD trivalent had a lower risk of influenza- or pneumonia-related hospitalization in the 2015/2016, 2013/2014, and 2012/2013 seasons and a lower risk of influenza-related outpatient visits in the 2017/2018 and 2012/2013 seasons. Compared to SD quadrivalent, HD trivalent was associated with a decreased risk of hospitalized influenza or pneumonia in 2013/2014 and a lower risk of influenza-related outpatient visits in 2014/2015. Compared to adjuvanted trivalent, HD trivalent was associated with a lower risk of influenza-related outpatient visits in 2017/2018.Results were presented in July 2020 for the CORE Summer Student Seminar Series at the Research Institute of the McGill University Health Centre and to the PHAC/NACI working group in November 2020. The final results were presented to the PHAC/NACI working group in February 2021.

Machado, M.A.d.A., Moura, C.S., Abrahamowicz, M. et al. Relative effectiveness of influenzavaccines in elderly persons in the United States, 2012/2013-2017/2018 seasons. npjVaccines 6, 108 (2021). https://doi.org/10.1038/s41541-021-00373-w