pmc.ncbi.nlm.nih.gov

Corrected human papillomavirus vaccination rates for each birth fiscal year in Japan

Abstract

In Japan, the serious adverse events after human papillomavirus (HPV) vaccination were widely reported in the media. The Ministry of Health, Labour and Welfare of Japan (MHLW) announced the suspension of the governmental recommendation of HPV vaccine in 2013, and the inoculation rate has since sharply declined. The estimated inoculation rate for each birth fiscal year (FY) announced by the MHLW and the actual numbers for each birth FY surveyed by local governments were very different. In particular, the cumulative vaccination rate of girls born in FY2000 was regarded to be as high as 42.9% by the Council of the MHLW. However, this estimation included a confusion. When the suspension of the governmental recommendation was announced in FY2013, the girls born in FY2000 turned 13 years old, the targeted starting age of the HPV vaccination. The vaccination rate of this generation is considered to be quite low. The numbers were recalculated in this study. This study revealed that the real vaccination rate is only 14.3%. Female individuals born in or after FY2000 have been confirmed to be exposed to the same cervical cancer risk as before the HPV vaccine was introduced in Japan.

Keywords: fiscal year, governmental suspension of recommendation, Japan, vaccination rate, vaccine

Corrected human papillomavirus vaccination rate for each birth fiscal year in Japan.

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1. INTRODUCTION

In Japan, the rate of age‐adjusted incidence of cervical cancer had been decreasing significantly in the 1980s and 1990s. However, the rate started to increase clearly after 2000. 1 Many cervical cancers are known to be caused by persistent infection with human papillomavirus (HPV), including HPV 16 and 18. Although cervical cancers caused by HPV 16 and 18 infection are vaccine‐preventable, the inoculation rate varies depending on the country. 2

In Japan, the emergency promotion project of HPV started in 2010. It targeted students in 7th to 10th grade (6th grade students were included in some local government areas.) The national HPV vaccination program started in April 2013, which targeted 7th grade (including 6th grade to 10th grade) students standardly. However, the serious adverse events after HPV vaccination were widely reported in the media. The Ministry of Health, Labour and Welfare of Japan (MHLW) announced the suspension of the governmental recommendation for HPV vaccination in 2013, and the inoculation rate has since sharply declined. 3 , 4 , 5 , 6 It is very important to recommend cervical cancer screening to the unvaccinated generation, and to resume the active recommendation of HPV vaccination. 7

To determine the inoculation rate of the HPV vaccine, each local government investigated the number of inoculations and the MHLW announced the estimated inoculation rate. However, the estimated inoculation rate and the actual numbers surveyed by the local governments were very different. For example, the inoculation rate of girls born in fiscal year (FY) 2000 was estimated to be 42.9% by the Council of the MHLW, 8 which was significantly higher than the inoculation rate of those in Sakai city in our previous report. 3 The aim of this study is to estimate the HPV vaccination rate of each birth FY more accurately for the prevention of cervical cancer. Girls born in or after FY2000, who have been supposed to have a lower vaccination rate, would now be expected to be sexually active. We need to understand the risk of developing cervical cancer of those females.

2. MATERIALS AND METHODS

The number of vaccinated girls, according to the Council of the MHLW, 8 is shown in Table 1. Their method of calculation is as follows. The HPV vaccination program in Japan involves three inoculations. The number of girls who had been vaccinated at least once are shown in Table 1 and “Age” represents the age at first inoculation.

TABLE 1.

Numbers of Japanese girls inoculated with human papillomavirus vaccine, according to the Council of the Ministry of Health, Labour and Welfare, Japan

Birth FY FY 2010 FY 2011 FY 2012 FY 2013 FY 2014 FY 2015 Number of female individuals Vaccinated rate
Age, y (vaccinated) Inoculation Age, Inoculation Age, y Inoculation Age, y Inoculation Age, y Inoculation Age, y Inoculation Cumulative inoculation Reference population (%)
1993 17 0 18 – 19 – 20 – 21 – 22 – 0 566 800 0.0
1994 16 178 852 17 71 307 18 – 19 – 20 – 21 – 250 159 592 400 42.2
1995 15 64 387 16 252 362 17 2928 18 – 19 – 20 – 319 677 589 300 54.2
1996 14 70 362 15 356 690 16 22 539 17 – 18 – 19 – 449 590 554 500 81.1
1997 13 60 149 14 348 607 15 45 916 16 2861 17 – 18 – 457 532 563 400 81.2
1998 12 4364 13 363 190 14 61 855 15 4780 16 136 17 – 434 325 576 700 75.3
1999 11 0 12 193 635 13 222 814 14 8518 15 443 16 67 425 476 573 800 74.2
2000 10 – 11 3418 12 190 636 13 50 552 14 979 15 220 245 805 572 400 42.9
2001 9 – 10 – 11 3373 12 29 440 13 1324 14 482 34 619 563 800 6.1
2002 8 – 9 – 10 – 11 2505 12 879 13 642 4026 551 700 0.7
2003 7 – 8 – 9 – 10 – 11 118 12 422 540 539 100 0.1
2004 6 – 7 – 8 – 9 – 10 – 11 55 55 539 100 0.0

They based their calculations on the implementation report of the emergency promotion project of HPV vaccination from FY2010 to FY2012. In FY2010, the age at the end of the FY was used. For example, all 6th grade girls were regarded as 12 years old (Figure 1A). In FY2011 and FY2012, the inoculation number in each grade was evenly divided into ages. For example, 6th grade girls were evenly divided into 11 years old and 12 years old (Figure 1B). In FY2013 and FY2014, the recording method was changed, and inoculation numbers were calculated from the data of the regional health promotion program report. The real age was used in the data, not the age of FY. For example, the girls vaccinated at 12 years old were recorded in the 12 y/o cell (Figure 1C). For FY2015, the MHLW obtained an estimate from the inoculation rate in FY2014 and halved the result. Data were published as estimated inoculation numbers on 1st October 2017. However, this estimation included data based on 2 different standards: one based on FY and the other on actual age.

FIGURE 1.

FIGURE 1

Method used by the Ministry of Health, Labour and Welfare of Japan (MHLW) to calculate the human papillomavirus vaccine uptake rates for the target girls according to birth fiscal year (FY). Age (y) in 2010 (A), 2011 (B), and 2013 (C). y/o, years old

In our calculation model, the standard was unified to FY in which girls were born. The numbers of inoculation in our model are based on the number of vaccinated girls announced by the Council of the MHLW 8 and the “Report on Regional Public Health Services and Health Promotion Services” published by MHLW. 9 , 10 , 11 , 12 , 13 The female reference population was calculated from the national population census. 14

3. RESULTS

The data of FY2010 shown by the Council of MHLW were acceptable. In the MHLW data, 6th grade girls in FY2011 were evenly divided into 11 and 12 years old. As 5th grade girls were not targeted for HPV vaccination, it is estimated that the inoculation number of 6th grade girls in FY2011 was approximately 6836, which is double 3418 allocated to 11 years old. The number of 7th grade girls vaccinated in FY2011 became 380 434, which is double 190 217, calculated by subtracting 3418 from 193 635 distributed to 12 years old. The inoculation number of 8th grade girls became 345 946, which is double 172 973, calculated by subtracting 190 217 from 363 190 distributed to 13 years old (Figure 2). All cells could be calculated in the same way as in FY2011 and FY2012.

FIGURE 2.

FIGURE 2

Method for correcting original data used by the Ministry of Health, Labour and Welfare of Japan (MHLW) to calculate human papillomavirus (HPV) vaccine uptake rates. FY, fiscal year

In FY2013, HPV vaccine became a routine immunization and the target was set to be from 6th to 10th grade with the standard target of 7th grade (13 years old). It is more accurate to estimate the inoculation number of 7th grade girls after fixing the numbers of 6th grade and 10th grade, while the numbers of 5th and 11th grade were considered to be almost zero. The inoculation number of 6th grade girls in FY2013 was 5010, which is double 2505, and that of 10th grade was 5722, which is double 2861 allocated to 16 years old. The number in 9th grade was 3838, which is double 1919, calculated by subtracting 2861 from 4780 who were inoculated at 15 years old. The inoculation number in 8th grade was 13 198, which is double 6599, calculated by subtracting 1919 from 8518 who were inoculated at 14 years old (Figure 2). The same calculation was done for FY2014, FY2015, and FY2016 and corrected data are shown in Table 2.

TABLE 2.

Corrected numbers of Japanese girls inoculated with human papillomavirus vaccine

Birth FY FY 2010 FY 2011 FY 2012 FY 2013 FY 2014 FY 2015 FY2016 FY2017 No. of female persons Vaccination rate
Age, y (vaccinated) Inoculation Age, y Inoculation Age, y Inoculation Age, y Inoculation Age, y Inoculation Age, y Inoculation Age, y Inoculation Age, y Inoculation Cumulative inoculation Reference population (%)
1993 17 – 18 – 19 – 20 – 21 – 22 – 23 – 24 – – – 0.0
1994 16 178 852 17 142 613 18 – 19 – 20 – 21 – 22 – 23 – 321 465 579 098 55.5
1995 15 64 387 16 362 112 17 5855 18 – 19 – 20 – 21 – 22 – 432 354 588 260 73.5
1996 14 70 362 15 351 268 16 39 224 17 – 18 – 19 – 20 – 21 – 460 854 589 312 78.2
1997 13 60 149 14 345 946 15 52 608 16 5722 17 – 18 – 19 – 20 – 464 425 589 055 78.8
1998 12 4364 13 380 434 14 71 102 15 3838 16 272 17 – 18 – 19 – 460 010 584 594 78.7
1999 11 – 12 6836 13 374 526 14 13 198 15 614 16 256 17 – 18 – 395 430 573 656 68.9
2000 10 – 11 – 12 6746 13 70 888 14 1344 15 1112 16 560 17 – 80 650 565 541 14.3
2001 9 – 10 – 11 – 12 5010 13 1413 14 294 15 534 16 1366 8617 553 103 1.6
2002 8 – 9 – 10 – 11 – 12 236 13 857 14 154 15 800 2047 543 086 0.4
2003 7 – 8 – 9 – 10 – 11 – 12 178 13 490 14 384 1052 529 073 0.2
2004 6 – 7 – 8 – 9 – 10 – 11 – 12 96 13 663 759 511 899 0.1
2005 5 – 6 – 7 – 8 – 9 – 10 – 11 – 12 134 134 522 030 0.0
2006 4 – 5 – 6 – 7 – 8 – 9 – 10 – 11 – – – 0.0

The cumulative vaccination rates for girls born in FY1999 and FY2000 were reported to be 74.2% and 42.9%, respectively, but they were revised to 68.9% and 14.3%, respectively, after the calculation (Figure 3).

FIGURE 3.

FIGURE 3

Year‐on‐year comparisons of the rates of human papillomavirus vaccination in Japan, estimated by the Ministry of Health, Labour and Welfare of Japan (MHLW) (filled columns) and our corrected rates (dotted fill). The corrected vaccination rate for female individuals born in fiscal year (FY) 2000 was found to be significantly lower than that estimated by the MHLW. Vaccination rates among generations born after FY2000 are considered to be quite low

4. DISCUSSION

In this study, HPV vaccination rates were recalculated based on data from the Council of the MHLW. Until now, the cumulative vaccination rate of girls born in FY2000 was regarded to be as high as 42.9%. When the suspension of the governmental recommendation was announced in FY2013, the girls born in FY2000 turned 13 years old, the starting age of the target of HPV vaccination. The vaccination rate of this generation is considered to be quite low. This study has revealed that the real vaccination rate is only 14.3%.

The most significant reason of this discrepancy is that there was a mix of FY‐based annual statistics and yearly surveys. Moreover, as the survey timing varied in each local government, it was difficult to determine the exact numbers of HPV vaccine recipients. In the estimates made by the Council of the MHLW, there is a problem in the statistical methods, such as dividing the inoculation number into 2 grades, one of which is not the target age for vaccination. By correcting this point, our estimate is closer to the real numbers in the local government surveys. Our estimate is considered to be useful for predicting the future incidence rate of cervical cancer.

Female individuals born in or after FY2000 have been confirmed to be exposed to the same cervical cancer risk as before the HPV vaccine was introduced in Japan. The vaccination rate for those born in FY2000 was found to be significantly lower than the MHLW data, so that their risk of future cervical cancer will return to the same level as the prevaccine generation. They will become the targets of cervical cancer screening at the age of 20 years after FY2020. Recommendation for cervical cancer screening should be strengthened for these women.

CONFLICT OF INTEREST

AY received a lecture fee from Merck Sharp & Dohme. YU received lecture fees, a research fund (grant number J550703673), and a consultation fee from Merck Sharp & Dohme. TK received a research fund (VT#55166) from Merck Sharp & Dohme. This study was partially funded by the Japan Agency for Medical Research and Development (grant number 15ck0106103h0102).

ACKNOWLEDGMENTS

We thank Ms Chihiro Tamura for her constructive critique and editing of our manuscript.

Nakagawa S, Ueda Y, Yagi A, Ikeda S, Hiramatsu K, Kimura T. Corrected human papillomavirus vaccination rates for each birth fiscal year in Japan. Cancer Sci. 2020;111:2156–2162. 10.1111/cas.14406

REFERENCES