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UBC Theses and Dissertations

Investigating the association of receipt of seasonal influenza vaccine with occurrence of anesthesia/paresthesia, headaches and generalized convulsive seizures for all ages, Canada 2012/13-2016/17 Ahmed, May


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 < 0.1%), while severe headaches were common (≥ 1% and < 10%), and GCS was a very rare (< 0.01%) AEFI. No associations were found for anesthesia/paresthesia and GCS. There was a higher risk of severe headaches that merits counseling at the time of vaccination. Ongoing monitoring is crucial to maintaining confidence in seasonal influenza vaccination safety.

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