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Introduction: The Canadian National Vaccine Safety (CANVAS) network collects seasonal influenza vaccine safety data from adults and children across Canada each year. Health events are evaluated between a vaccinated group and an unvaccinated group using data from online surveys. This thesis aims to describe the rate of severe health events and the most severe symptoms following seasonal influenza vaccination compared to an unvaccinated group of children and pregnant people. In addition, it aims to determine the agreement between symptoms reported in the online survey and a follow-up telephone report. Methods: Uncorrelated data from the CANVAS network were analyzed from 2013/2014 to 2019/2020. The outcome of interest was a severe health event that prevented/stopped daily activities, missed school, or required medical consultation. Incidence rate ratios and logistic regressions were conducted for both groups of interest to determine the association between vaccination status and severe health events. The sensitivity, specificity, and kappa estimate were calculated to determine the agreement for the most severe symptom, diagnosis, and treatment. Results: The unadjusted rate ratio for severe health events in children who received the inactivated influenza vaccine (IIV) compared to unvaccinated children was 1.22 (1.10, 1.34). However, no differences were observed in children who received the live attenuated influenza vaccine (LAIV) compared to an unvaccinated child group. The adjusted odds ratio (OR) for severe health events in children who received IIV compared to unvaccinated children was 1.11 (1.00, 1.25), and 1.11 (0.95, 1.29) in children who received LAIV compared to unvaccinated children. The agreement between child responses in the self-report online survey and the telephone report was moderate-to-high in both vaccinated and unvaccinated participants combined. The unadjusted rate ratio for severe health events in vaccinated pregnant people compared to unvaccinated pregnant people was 1.00 (0.64, 1.58). The adjusted OR for severe health events in vaccinated compared to unvaccinated pregnant people was 0.95 (0.59, 1.53). Conclusion: The findings show no association between the seasonal influenza vaccine and severe health events in children and pregnant people in Canada. There was moderate to high agreement of child responses between the online survey and the telephone report.

Introduction/background: Concern about adverse events following immunization (AEFI) is frequently cited by both those who receive vaccines and those who decline to receive vaccines. Neurological adverse events are especially concerning. Our aim is to detect associations for occurrence of anesthesia/paresthesia (numbness, tingling, pins and needles, decreased sensation, or burning sensations anywhere in the body), severe headaches, and generalized convulsive seizures (GCS) in the presence and absence of seasonal influenza vaccination.Methods: Data were analyzed from the Canadian National Vaccine Safety Network that annually collects safety data during the seasonal influenza vaccination campaign. Events were self-reported and prevented daily activity, led to absenteeism, or required medical attention. Controls were previous year vaccinees; events in controls were collected prior to the start of influenza vaccination each year. Total sample size for investigating anesthesia/paresthesia was 107,565 from 2012-2016, and 97,420 for investigating severe headaches and GCS from 2013-2016. Multivariable logistic regression was used to determine the association between seasonal influenza vaccination and occurrence of anesthesia/paresthesia or severe headaches adjusted for gender, age group, reporting center, and year. Fisher’s exact test was used to measure risk of occurrence of GCS.Results: 104 (0.10%) participants reported anesthesia/paresthesia; 63 (0.09%) versus 41 (0.11%) in vaccinees and controls, respectively. Severe headaches were reported by 1,361 (1.40%) participants; 907 (1.48%) versus 454 (1.26%) in vaccinees and controls, respectively. Adjusted OR of anesthesia/paresthesia among those with seasonal influenza vaccination was 0.89 (95% CI = 0.60, 1.32), and of severe headaches was 1.21 (95% CI = 1.08, 1.36). No specific vaccine product was associated with this increased risk. Three participants were identified with GCS; difference in proportions between groups was not statistically significant (p = 0.301).Conclusions: Results are reassuring on the safety of seasonal influenza vaccines. Anesthesia/paresthesia was rare (≥ 0.01 and