(274) Risk of Stroke Following Influenza Vaccination in Elderly: A National-Based Self-Controlled Case Series Study in Korea

Sunday, August 28, 2022

8:00 AM – 1:45 PM CEST

Location: Hall C

Publication Number: 1319

Presenting Author(s)

Heejin Kim
– Ewha Womans University, Seodaemungu, South Korea

Co-Author(s)

Joongyub Lee
– Department of Preventive Medicine, Seoul National University, Seoul, Republic of Korea
EUNSUN LIM
– Seodaemun-gu, South Korea
Haerin Cho
– Ewha university, Seodaemun-gu, South Korea
HeeHyun Won
– Ewha Womans University, Seodaemun-Gu, South Korea
Nam-Kyong Choi
– Department of Health Convergence, College of Science & Industry Convergence, Ewha Womans University, Seoul, Republic of Korea, Republic of Korea

Background: National influenza vaccination program is operated for the elderly over 65 years in Korea. Despite the several studies related association of influenza vaccine and stroke, few studies were performed for Asian elderly. A large study based on a national population is needed to provide clear evidence of an association between influenza vaccine and stroke risk in Asians.

Objectives: We aimed to confirm whether influenza vaccination is associated with stroke for the elderly population in Korea using a large-scale national database.

Methods: We identified patients who had one or more stroke hospitalization episodes from September 1, 2017 to October 30, 2018 using a large-linked database of vaccination registration data from the Korea Disease Control and Prevention Agency and the National Health Insurance Service claims data. The cases were restricted to those who received only one influenza vaccine between September 1, 2017 and April 30, 2018 (17/18 season), and patients who experienced a stroke on same or before their vaccination date was excluded. We defined stroke patients as only those who had both the ICD-10 code (I60, I61, I63) and the related operation code. Using the self-controlled case series (SCCS) study design, we followed up patients for 6 month (180 days) from the days of vaccination. The risk period and control period was defined as 1 to 14 days and 15 to 180 days following vaccination, respectively. The incidence rate ratio (IRR) between the risk period and the control period was calculated.

Results: A total of 4,316 elderly aged 65 years or older were identified who were firstly diagnosed with a stroke following vaccination during the observation period. Most of them were vaccinated between September and December (98.3%). There were 324 (7.5%) patients who had a stroke within 14 days after vaccination and the follow-up period was 164.8 and 1579 person-years for the patients of risk-period and control-period, respectively. The risk of stroke was significantly reduced by 22% in the risk-period compared to the control-period (IRR 0.78, 95% Confidence interval 0.70-0.87; p-value < 0.001).

Conclusions: In our study, influenza vaccination had advantage in reduction the risk of stroke among elderly, which is consistent with the results of previous studies. These results support national efforts to encourage influenza vaccination for the elderly in Korea.