Patterns of High vs. Standard Dose Flu Vaccinations in Canadian Primary Care: A Baseline Cohort Pilot Study

Context: The high dose flu vaccination is newly available to Canadians and recommended for adults aged 65 years and older. Describing patterns of flu vaccination in Canadian primary care using electronic medical records (EMR) is challenging. However, we have established that by using a combination of the ATC code and the lot number of the product administered, we can differentiate between high and standard dose flu vaccination using routinely collected structured EMR data.

Objectives: 1) Construct a baseline cohort of patients who received a flu vaccine during the 2018-2019 and 2019-2020 flu seasons. 2) Describe age, SES and comorbidity related patterns of standard vs. high dose flu vaccination.

Design: Baseline cohort pilot study

Dataset: Data from the Eastern Ontario Network (EON), a repository of EMR data drawn from primary care practices in south-eastern Ontario.

Population Studied: Patients aged 65 and older who received a flu vaccination in a primary care setting during the 2018-2019 and/or 2019-2020 flu seasons (June 1 2018-May 31 2020).

Outcome Measures: Flu vaccinations were determined by ATC code (J07BB). All patients who were vaccinated with a high dose lot number product were classified as “high dose”, all others were classified as “standard dose”. Logistic regression was used to describe odds of high vs standard dose flu vaccinations related to age, sex, location, socioeconomic status, and comorbidity.

Results: Baseline cohorts of patients aged 65 and older who received flu vaccinations during the 2018-2019 (n=19,037) and 2019-2020 (n=18,908) flu seasons were constructed. Over one-third of patients 65 and older received a high dose flu vaccination in the 2018-2019 (36.6%) and 2019-2020 (35.4%) flu seasons. Both cohorts (2019-2019 vs 2019-2020) were also similar in age (75.8±7.6 vs. 75.9±7.6 years old), sex (54.6% vs. 54.2% female), and location (65.2% vs 64.2% live in an urban setting). Age was the strongest predictor of having received a high dose flu vaccine for both cohorts. Patients aged 85 years and older were 1.44x (95% CI 1.29-162; 2018-2019) and 1.86x (95% CI 1.65-2.08; 2019-2020) more likely to have received a high dose flu vaccine compared to patients aged 65 to 69.

Conclusion: Overall, Canadian primary care EMR data was effectively used to compare patterns of high and standard dose flu vaccinations in patients aged 65+. Future work will describe patterns of subsequent respiratory infections stratified by flu vaccine dose.