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1Department of Big Data Strategy, National Health Insurance Services, Wonju, Korea
2Sungkyunkwan University School of Pharmacy, Suwon, Korea
3Department of Obstetrics & Gynecology, CHA Ilsan Medical Center, Goyang, Korea
4Division of Immunization, Bureau of Healthcare Safety and Immunization, Korea Disease Control and Prevention Agency, Cheongju, Korea
5Division of Immunization Planning, Bureau of Healthcare Safety and Immunization, Korea Disease Control and Prevention Agency, Cheongju, Korea
6Health Insurance Research Institute, National Health Insurance Services, Wonju, Korea
© 2024, Korean Society of Epidemiology
This is an open-access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Conflict of interest
The authors have no conflicts of interest to declare for this study.
Funding
None.
Author contributions
Conceptualization: Kim JY, Cho J, Kim EM, Kim JH, Shin JY, Kim EH. Data curation: Cho J, Kim EM. Formal analysis: Cho J, Kim EM. Funding acquisition: None. Methodology: Cho J, Kim EM, Kim JH, Shin JY. Project administration: Cho J. Visualization: Cho J. Writing – original draft: Cho J, Kim EM, Kim JH, Shin JY, Kim EH, Park JH, Kwon SL, Kwon GY, Shin SA, Kim JY. Writing – review & editing: Cho J, Kim EM, Kim JH, Kim JY.
Subgroup | Follow-up period; Baseline to cut-off year (conditional status) | Vaccination status | n | Person-years | No. of event cases | HR (95% CI)1 |
---|---|---|---|---|---|---|
All | Baseline to Year 1 (entire population) | Y | 166,031 | 166,021 | 13 | 1.29 (0.57, 2.94) |
N | 166,031 | 166,014 | 10 | 1.00 (reference) | ||
Baseline to Year 2 (first-year survivors)2 | Y | 165,976 | 165,971 | 13 | 0.62 (0.31, 1.13) | |
N | 165,976 | 165,963 | 21 | 1.00 (reference) | ||
Baseline to Year 3 (second-year survivors)2 | Y | 165,895 | 165,889 | 23 | 0.58 (0.35, 0.96) | |
N | 165,895 | 165,884 | 40 | 1.00 (reference) | ||
Baseline to Year 4 and beyond (third-year survivors)2 | Y | 165,788 | 138,063 | 57 | 0.39 (0.28, 0.52) | |
N | 165,788 | 138,047 | 148 | 1.00 (reference) | ||
Birth year 2003 | Baseline to Year 1 (entire population) | Y | 84,187 | 84,180 | 9 | 1.29 (0.48, 3.46) |
N | 84,187 | 84,179 | 7 | 1.00 (reference) | ||
Baseline to Year 2 (first-year survivors)2 | Y | 84,157 | 84,153 | 8 | 0.44 (0.19, 1.01) | |
N | 84,157 | 84,149 | 18 | 1.00 (reference) | ||
Baseline to Year 3 (second-year survivors)2 | Y | 84,101 | 84,098 | 12 | 0.48 (0.24, 0.96) | |
N | 84,101 | 84,095 | 25 | 1.00 (reference) | ||
Baseline to Year 4 and beyond (third-year survivors)2 | Y | 84,039 | 71,052 | 36 | 0.38 (0.26, 0.55) | |
N | 84,039 | 71,043 | 96 | 1.00 (reference) | ||
Birth year 2004 | Baseline to Year 1 (entire population) | Y | 60,795 | 60,794 | 2 | N/A3 |
N | 60,795 | 60,790 | 2 | |||
Baseline to Year 2 (first-year survivors)2 | Y | 60,779 | 60,778 | 4 | N/A3 | |
N | 60,779 | 60,776 | 2 | |||
Baseline to Year 3 (second-year survivors)2 | Y | 60,763 | 60,761 | 7 | 0.63 (0.25, 1.63) | |
N | 60,763 | 60,760 | 11 | 1.00 (reference) | ||
Baseline to Year 4 and beyond (third-year survivors)2 | Y | 60,734 | 51,061 | 20 | 0.44 (0.26, 0.75) | |
N | 60,734 | 51,056 | 45 | 1.00 (reference) |
CI, confidence interval; Y, yes (vaccinated); N, no (unvaccinated).
1 HR adjusted for birth year, socioeconomic status, and regional urbanization level.
2 Prior to each stratified period, the following were excluded: persons diagnosed with genital warts, persons who had been censored, and their matched counterparts.
3 Results were not estimated due to an insufficient number of events.
Characteristics | Before matching |
After matching |
||||
---|---|---|---|---|---|---|
HPV-vaccinated group | HPV-unvaccinated group | p-value | HPV-vaccinated group | HPV-unvaccinated group | p-value | |
Total no. of individuals | 184,359 (50.6) | 180,032 (49.4) | - | 166,031 (50.0) | 166,031 (50.0) | - |
Follow-up duration (yr) | 4.58±0.30 | 4.66±0.37 | - | 4.58±0.30 | 4.58±0.30 | - |
Birth year | <0.05 | N.S. | ||||
2003 | 86,830 (47.1) | 91,881 (51.0) | 84,187 (50.7) | 84,187 (50.7) | ||
2004 | 75,369 (40.9) | 62,065 (34.5) | 60,795 (36.6) | 60,795 (36.6) | ||
2005 | 22,160 (12.0) | 26,086 (14.5) | 21,049 (12.7) | 21,049 (12.7) | ||
Age (at date of first follow-up) | 13.30±0.68 | 13.24±0.78 | <0.05 | 13.32±0.70 | 13.31±0.70 | N.S. |
Birth year 2003 | 13.87±0.38 | 13.85±0.44 | 13.86±0.38 | 13.86±0.38 | ||
Birth year 2004 | 12.90±0.40 | 12.84±0.42 | 12.89±0.40 | 12.89±0.40 | ||
Birth year 2005 | 12.38±0.33 | 12.14±0.60 | 12.37±0.33 | 12.33±0.32 | ||
Age (at date of last follow-up) | 17.88±0.74 | 17.83±0.78 | <0.05 | 17.85±0.75 | 17.86±0.76 | N.S. |
Birth year 2003 | 18.52±0.30 | 18.46±0.31 | 18.47±0.30 | 18.47±0.31 | ||
Birth year 2004 | 17.53±0.30 | 17.47±0.30 | 17.48±0.30 | 17.47±0.30 | ||
Birth year 2005 | 16.56±0.30 | 16.46±0.31 | 16.51±0.30 | 16.46±0.30 | ||
Type of vaccine | - | - | ||||
4-valent | 184,093 (99.9) | N/A | 165,831 (99.9) | N/A | ||
9-valent | 266 (0.1) | N/A | 200 (0.1) | N/A | ||
Socioeconomic status | <0.05 | N.S. | ||||
Medical Aid | 5,714 (3.1) | 6,240 (3.5) | 5,266 (3.2) | 5,266 (3.2) | ||
Lowest | 41,928 (22.7) | 40,012 (22.2) | 36,827 (22.2) | 36,827 (22.2) | ||
Low | 28,803 (15.6) | 28,143 (15.6) | 25,754 (15.5) | 25,754 (15.5) | ||
Middle | 33,850 (18.4) | 32,082 (17.8) | 29,966 (18.1) | 29,966 (18.1) | ||
High | 40,795 (22.1) | 38,344 (21.3) | 36,519 (22.0) | 36,519 (22.0) | ||
Highest | 33,269 (18.1) | 35,211 (19.6) | 31,699 (19.1) | 31,699 (19.1) | ||
Regional urbanization level | <0.05 | <0.05 | ||||
Metropolis | 113,038 (61.3) | 112,221 (62.3) | 104,691 (63.1) | 107,670 (64.8) | ||
Urban | 58,215 (31.6) | 56,777 (31.5) | 50,867 (30.6) | 49,370 (29.7) | ||
Rural | 13,106 (7.1) | 11,034 (6.1) | 10,473 (6.3) | 8,991 (5.4) |
Subgroup | Follow-up period; Baseline to cut-off year (conditional status) | Vaccination status | n | Person-years | No. of event cases | HR (95% CI) |
---|---|---|---|---|---|---|
All | Baseline to Year 1 (entire population) | Y | 166,031 | 166,021 | 13 | 1.29 (0.57, 2.94) |
N | 166,031 | 166,014 | 10 | 1.00 (reference) | ||
Baseline to Year 2 (first-year survivors) |
Y | 165,976 | 165,971 | 13 | 0.62 (0.31, 1.13) | |
N | 165,976 | 165,963 | 21 | 1.00 (reference) | ||
Baseline to Year 3 (second-year survivors) |
Y | 165,895 | 165,889 | 23 | 0.58 (0.35, 0.96) | |
N | 165,895 | 165,884 | 40 | 1.00 (reference) | ||
Baseline to Year 4 and beyond (third-year survivors) |
Y | 165,788 | 138,063 | 57 | 0.39 (0.28, 0.52) | |
N | 165,788 | 138,047 | 148 | 1.00 (reference) | ||
Birth year 2003 | Baseline to Year 1 (entire population) | Y | 84,187 | 84,180 | 9 | 1.29 (0.48, 3.46) |
N | 84,187 | 84,179 | 7 | 1.00 (reference) | ||
Baseline to Year 2 (first-year survivors) |
Y | 84,157 | 84,153 | 8 | 0.44 (0.19, 1.01) | |
N | 84,157 | 84,149 | 18 | 1.00 (reference) | ||
Baseline to Year 3 (second-year survivors) |
Y | 84,101 | 84,098 | 12 | 0.48 (0.24, 0.96) | |
N | 84,101 | 84,095 | 25 | 1.00 (reference) | ||
Baseline to Year 4 and beyond (third-year survivors) |
Y | 84,039 | 71,052 | 36 | 0.38 (0.26, 0.55) | |
N | 84,039 | 71,043 | 96 | 1.00 (reference) | ||
Birth year 2004 | Baseline to Year 1 (entire population) | Y | 60,795 | 60,794 | 2 | N/A |
N | 60,795 | 60,790 | 2 | |||
Baseline to Year 2 (first-year survivors) |
Y | 60,779 | 60,778 | 4 | N/A |
|
N | 60,779 | 60,776 | 2 | |||
Baseline to Year 3 (second-year survivors) |
Y | 60,763 | 60,761 | 7 | 0.63 (0.25, 1.63) | |
N | 60,763 | 60,760 | 11 | 1.00 (reference) | ||
Baseline to Year 4 and beyond (third-year survivors) |
Y | 60,734 | 51,061 | 20 | 0.44 (0.26, 0.75) | |
N | 60,734 | 51,056 | 45 | 1.00 (reference) |
Values are presented as number (%) or mean±standard deviation. HPV, human papillomavirus; N/A, not applicable; N.S., not significant.
CI, confidence interval; Y, yes (vaccinated); N, no (unvaccinated). HR adjusted for birth year, socioeconomic status, and regional urbanization level. Prior to each stratified period, the following were excluded: persons diagnosed with genital warts, persons who had been censored, and their matched counterparts. Results were not estimated due to an insufficient number of events.