Table 3. Estimated β-coefficients of odds ratios with 95% CIs by KNHANES from 2007 to 2020

	Trends in influenza vaccination			Odds ratios for influenza vaccination (95% CI)
	Pre-pandemic trend, β (95% CI) 2007 to 2019	Pandemic trend, β (95% CI) 2018 to 2020	Trend difference, βdiff (95% CI)	Crude	Adjusted*
Overall	0.310 (0.267–0.352)	0.036 (0.010–0.062)	-0.274 (-0.323 to -0.224)	1.155 (1.039–1.284)	1.175 (1.051–1.312)
Age, years
14–18	0.337 (0.186–0.488)	0.175 (0.079–0.271)	-0.162 (-0.341 to 0.017)	2.026 (1.363–3.010)	2.084 (1.400–3.102)
19–64	0.263 (0.215–0.310)	0.051 (0.022–0.081)	-0.211 (-0.267 to -0.156)	1.228 (1.090–1.383)	1.217 (1.077–1.375)
≥65	0.457 (0.368–0.547)	-0.074 (-0.128 to -0.020)	-0.532 (-0.636 to -0.427)	0.743 (0.598–0.923)	0.753 (0.603–0.942)
Sex
Male	0.279 (0.224–0.334)	0.044 (0.010–0.078)	-0.235 (-0.300 to -0.171)	1.192 (1.040–1.366)	1.209 (1.050–1.392)
Female	0.339 (0.291–0.387)	0.031 (-0.001 to 0.063)	-0.308 (-0.366 to -0.251)	1.132 (0.998–1.285)	1.144 (1.001–1.308)
Income
Lowest quartile	0.360 (0.284–0.436)	0.008 (-0.036 to 0.053)	-0.352 (-0.440 to -0.264)	1.035 (0.864 to 1.239)	1.017 (0.838–1.235)
Second quartile	0.258 (0.184–0.331)	0.054 (0.008–0.100)	-0.204 (-0.291 to -0.117)	1.241 (1.032–1.492)	1.289 (1.062–1.565)
Third quartile	0.313 (0.240–0.387)	0.065 (0.021–0.110)	-0.248 (-0.333 to -0.162)	1.300 (1.089–1.552)	1.331 (1.097–1.615)
Highest quartile	0.308 (0.231–0.384)	0.013 (-0.033 to 0.058)	-0.295 (-0.384 to -0.206)	1.052 (0.876–1.262)	1.067 (0.874–1.302)
Medical condition
With medical condition	0.315 (0.254–0.376)	-0.005 (-0.041 to 0.031)	-0.320 (-0.391 to -0.250)	0.980 (0.848–1.132)	1.044 (0.906–1.202)
Without medical condition	0.253 (0.201–0.304)	0.056 (0.024–0.088)	-0.197 (-0.257 to -0.136)	1.250 (1.100–1.420)	1.258 (1.103–1.435)

Abbreviations: CI, confidence interval; KNHANES, Korea National Health and Nutrition Examination Survey
Medical conditions include one or more of the following conditions: diabetes, tuberculosis, asthma, angina, myocardial infarction, cancer, chronic kidney disease, hypertension, and hyperlipidemia.
The model was adjusted for age (14–18, 19–64, and ≥65 years), sex, obesity (<18.5, 18.5–23.0, 23.0–25.0, and ≥25.0 kg/m²), income (lower, lower-middle, higher-middle, and highest quartile), education level, alcohol consumption, smoking status, nationwide health screening within 2 years, and medical condition.
Numbers in bold indicate a significant difference (P < 0.05).