Impact of local vaccine subsidization programs on the prevention of mumps in Japan

ABSTRACT

In Japan, although a mumps vaccination is outside the national universal vaccination program, some local governments have implemented their own program. However, little is known regarding the implementation status and the impact of these programs. In this study, we investigated the impact on the prevention of mumps, after identification of the status of the local government subsidization programs. We identified the implementation status of the subsidization programs using the websites of local governments. We retrieved the number of reported mumps cases from designated sentinel sites through the Surveillance of Infectious Diseases System implemented according to the Infectious Disease Control Law. Using this data, the impact of the subsidization program on prevention of mumps was assessed by comparing the number of mumps cases per site during the 2015–2016 outbreak among the areas categorized by the subsidization status, using a Poisson regression model. As of 2019, 26.2% (456/1,739) of the local governments were considered as having subsidization programs. We retrieved 52,719 mumps cases from 2010 to 2019. The number of mumps cases per sentinel site tended to be low in areas implementing a subsidization program, compared with the no-implementation areas throughout the data collection period. The adjusted model confirmed that the subsidization program implemented between 2010 and 2015 impacted on the number of mumps cases during the 2015–2016 outbreak, with a decrease in the numbers. Further studies with detailed data including vaccination coverage should be conducted.

KEYWORDS:

• Local subsidization
• mumps vaccination
• prevention
• impact of mumps vaccination
• Japan

1. Introduction

Mumps, one of the most common childhood viral diseases affecting children mainly between the ages of 5 and 9 years, is characterized by swelling of the parotid gland.¹ Its complications are likely to be severe, especially for infected adults, including meningitis, encephalitis, orchitis and deafness.^1,2 A vaccine can prevent the disease; therefore, many countries included the mumps vaccine in national universal vaccination programs. This has seen the incidence drop dramatically.² In Japan, a voluntary vaccination of monovalent mumps was introduced in 1981, and subsequently measles-mumps-rubella (MMR) vaccines were introduced and included into a national universal vaccination program in 1989.^3,4 However, MMR vaccines were discontinued in 1993 due to aseptic meningitis following vaccination. As monovalent mumps vaccines were again used thereafter as a voluntary vaccination, vaccination coverage declined, and a large mumps outbreak has occurred every 4–5 years.^4,5 Previous surveillance and studies have indicated that the last two outbreaks were from 2010 to 2011 and from 2015 to 2016.^6,7 During the last outbreak period in 2015 and 2016, the National Surveillance indicated that there were 240,042 mumps cases from approximately 3,000 sentinel sites.⁵ Another study also found that 359 children developed mumps-related hearing loss from 3,906 medical institutions in Japan.⁷

Although mumps vaccination remains outside the national universal vaccination program, some local governments have implemented their own subsidization program for mumps vaccinations. Previous studies have shown that one of the key reasons for non-vaccination in voluntary vaccinations was the cost.^8,9 Thus, it would be expected that a subsidization program would increase vaccination coverage. According to the National Survey in 2010 and 2012,^10,11 mumps vaccinations were locally subsidized in 61 (3.5%) and 191 administrative districts (11.0%), respectively. However, there was no formal updated survey to assess the success of its implementation. Furthermore, the impact of the subsidization programs for mumps has not been well assessed, especially on a large scale. There is only one previous study that showed the reduction in the occurrence of mumps between pre-/post-subsidization in one city.¹² Overall, there have been little or no formal studies, to date, regarding the updated implementation status of local subsidization programs in Japan and their impact on the prevention of mumps. Therefore, in this study, we aimed to identify the status of subsidization programs by local governments and investigate their impact on the prevention of mumps.

2. Materials and methods

2.1. Identification of the status of subsidization programs by local governments

The information on subsidization programs by local governments was obtained from their websites. After a preliminary evaluation of a sample of 10 websites, the following information was obtained: First, the local governments were identified from a list that was provided by the Ministry of Internal Affairs and Communications, a national department.¹³ Second, the websites were identified by searching for the name of the local governments using the Google search engine. Third, webpages regarding immunizations were identified by searching within their websites, using Japanese keywords for “immunization,” “vaccination,” or “vaccine.” Finally, specific information regarding subsidization programs were obtained from the searched pages. The information was obtained by one person and then confirmed by another person independently.

2.2. Categorization of the subsidization program status

To understand the impact of the subsidization programs, we considered three subsidization statuses: 1) a well-implemented area where the subsidization program was implemented before 2010, with the assumption that the population had been well immunized throughout the study period (2010–2019); 2) an implemented area where the subsidization program was implemented after 2010, but before 2015, with the assumption that while the population had not been immunized at the 2010–2011 outbreak, they were immunized at the 2015–2016 outbreak through the program; and 3) an no-implementation area where there was no subsidization program implemented before 2015. Accordingly, to gain sufficient data for each of the three categories, we considered Tokyo and Ibaraki as a prefectures of interest, as they were the only prefectures where the subsidization program had been implemented in more than three large administrative districts (population > 50,000), according to a previous survey in 2010.¹⁰ Tokyo includes the capital of Japan and Ibaraki is known one of the suburbs on Tokyo. For the categorization, we considered a public healthcare center-based area, as the number of mumps cases under Surveillance of Infectious Diseases System is made public on the orders of the healthcare center-based area, and not the administrative districts-based area. When the subsidization status was different between administrative districts in the same healthcare center-based area, the status in the most populated area was selected (e.g., when a healthcare center-based area covered two administrative districts which subsidization status was different each other, the status of subsidization in the more populated district was selected).

2.3. Identification of mumps cases and their trends

The number of mumps cases during the latest 10 years (from 2010 to 2019) were retrieved from the website of public healthcare centers or governments in a prefecture of interest.^14,15 The information was collected from the Surveillance of Infectious Diseases System, which is the system implemented according to the Infectious Disease Control Law. In Japan, each local government has designated medical institutions as sentinel sites in a random manner, taking into consideration the population and distribution of the healthcare institutions in the area. There are approximately 3,000 pediatric sentinel sites in Japan for pediatric infections including mumps.¹⁶ The designated sentinel sites are required to report the number of infection cases, including mumps, to public health centers located in the same area. The reporting criteria for mumps is when a patient was diagnosed as having mumps with a sudden swelling of one or both parotid glands which continued more than 2 days and there is no other reasonable cause of the swelling.¹⁷ Finally, each public healthcare center or government accumulates reports from the sites and is required to disclose the number of infection cases including mumps to the public, e.g. through their websites.^14,15

To understand the trends in the number of mumps cases in the prefectures of interest, the annual number of mumps cases divided by the annual number of sentinel sites in each public health center-based area was calculated. Although the sentinel sites had been designated annually, some sentinel sites had been designated for a period shorter than a year. In such cases, the period was converted to an annual-based period, e.g. when a site was designated for 10 weeks within a year (52 or 53 weeks), a contribution of the site was not considered as one, but as 10 divided by 52 or 53 when calculating the annual number of sentinel sites.

2.4. Impact of the subsidization program on the prevention of mumps

The number of mumps cases per site during the 2010–2011 and 2015–2016 outbreaks between the prefectures and among the categories of subsidization status were summarized. Thereafter, to investigate impact of the subsidization program on prevention of mumps, the number of mumps cases per site during the 2015–2016 outbreak was compared among the areas categorized by the subsidization status, using a Poisson regression model. For the adjusted model, the number of mumps cases per site during the 2010–2011 outbreak, population density, pediatric population, and a change of the pediatric population from 2010 to 2015 were controlled. Well-implemented areas were excluded from the analysis using the adjusted model, because it was considered that the subsidization had already impacted several mumps cases during the 2010–2011 outbreak. In addition, an analysis for each prefecture was performed to understand the differences of the impact among the prefectures. All the statistical analyses were performed with SAS version 9.4 (SAS Institute, Inc., Cary, NC, USA).

3. Results

3.1. Identification of the status of subsidization program by local governments

We identified 1,739 local governments (administrative districts) from 47 prefectures in Japan. When searching through Google, from December 2019 to March 2020, all the local governments were found to have their own websites. For the subsidization of mumps, 26.2% of the local governments (456/1,739) were considered as having a subsidization program from the information on the website. According to the latest National Survey conducted in 2015,¹⁸ these covered 26.5% of the Japanese population. The subsidization coverage and eligibility varied among the local governments; many subsidization programs only covered the partial cost of the mumps vaccination; the amount varied, and two doses were not necessarily covered. No prefecture, except Tokyo and Ibaraki, met the criteria for the prefecture of interest.

3.2. Categorization of the subsidization program status

Characteristics of the prefectures were shown in Table 1. There were 12 and 31 healthcare center-based areas in Ibaraki and Tokyo, respectively, which covered 44 and 62 administrative districts and constituted 75.3 and 239.3 sentinel sites as yearly average. A proportion of implementation of subsidization (the number of well-implemented or implemented area vs. the number of no-implementation area) was 33.3% (4/12) in Ibaraki and 41.9% (13/31) in Tokyo, respectively, at the start of the 2015–2016 outbreak (at the beginning of 2015). With population data from the National Survey,¹⁸ the population density was relatively high compared to in Ibaraki and the pediatric population (under 15) increased from 2010 to 2015 in Tokyo. For the status of the subsidization program in Tokyo, areas where the population density was high tended to be subsidized and where the pediatric population was not necessarily high, in contrast to Ibaraki where areas where the pediatric population was high tended to be subsidized.

Table 1. Characteristics of prefectures of interest

Prefecture	Category of subsidization status	Areas (N)	Administrative districts (N)	Sentinel Sites ^1 (N on yearly average)	Population ^2 (×10^3)	Population density ^2 (×10^3/km^2)	Population per site ^2 (×10^3/site)	Pediatric population per site ^2 (×10^3/site)	Change of pediatric population ^3
Ibaraki	Well-implemented area	2	9	19.0	727	0.8	38.3	4.7	0.90
	Implemented area	2	13	14.0	633	0.7	45.2	5.4	0.91
	No-implementation area	8	22	42.4	1,557	0.7	37.1	4.7	0.92
	Total	12	44	75.3	2,917	0.7	38.9	4.8	0.91
Tokyo	Well-implemented area	1	1	7.6	387	16.9	48.4	5.3	1.12
	Implemented area	12	12	70.1	3,879	16.0	55.4	5.6	1.10
	No-implementation area	18	49	161.6	9,250	8.3	57.1	6.7	1.00
	Total	31	62	239.3	13,515	9.8	56.5	6.3	1.03
Overall	Well-implemented area	3	10	26.5	1,114	1.1	41.3	4.9	0.96
	Implemented area	14	25	84.1	4,511	3.8	53.7	5.6	1.06
	No-implementation area	26	71	204.0	10,807	3.4	53.0	6.3	0.99
	Total	43	106	314.7	16,432	3.1	52.2	6.0	1.00

¹Number of sentinel sites did not become an integral number as the period for a sentinel site designated for shorter than a year was converted to yearly-based period. ² Data of populations and population density were referred from the latest National Survey conducted in 2015. For pediatric population, population under 15 was referred. ³ Change of pediatric population was calculated as pediatric population in 2015 divided by that in 2010, with a reference of the National Survey in 2010 and 2015.

N: number

3.3. Identification of mumps cases and their trends

From 2010 to 2019, a total of 52,719 mumps cases were retrieved (36,835 cases in Tokyo and 15,884 in Ibaraki) from the website of each public healthcare center in the prefectures of interest. Of these, 2,760 cases were reported from the well-implemented areas, 10,474 cases from the implemented areas and the other 39,485 cases were from the no-implementation areas.

Trends in the number of mumps cases per sentinel site from 2010 to 2019 is summarized in Table 2 and Figure 1. Overall, peaks were observed during 2010–2011 and 2015–2016 among the well-implemented, implemented and no-implementation areas. The number of mumps cases per sentinel site tended to be lower in the implemented and well-implemented areas than in the no-implementation areas throughout the data period. The number of cases per site were lower in the well-implemented areas compared to the implemented areas; however, they were the same, especially during the outbreak periods such as in 2010 and 2016. Similar patterns were observed in each prefecture; however, the overall trend tended to be higher in Ibaraki compared to Tokyo (Figure 2). The number of mumps cases per sentinel site during the 2010–2011 period was at the same level in the implemented areas and no-implementation areas in Ibaraki; however, this was not the case in Tokyo.

Table 2. Annual number of mumps cases per sentinel site between the prefectures and among categories of subsidization status from 2010 to 2019

Prefecture	Category of subsidization status	Number of mumps cases per sentinel site (number of mumps cases/number of sentinel sites ^1)
		2010	2011	2012	2013	2014	2015	2016	2017	2018	2019
Ibaraki	Well-implemented area	35.1	23.6	6.3	3.4	3.2	12.4	20.7	4.7	3.0	3.6
		(667/19)	(448/19)	(120/19)	(64/19)	(61/19)	(236/19)	(394/19)	(89/18.9)	(57/19)	(68/18.8)
	Implemented area	63.8	66.3	11.6	7.9	5.1	16.1	28.4	6.4	3.7	6.0
		(893/14)	(928/14)	(162/14)	(110/13.9)	(72/14)	(224/13.9)	(396/14)	(90/14)	(51/13.6)	(80/13.4)
	No-implementation area	64.5	45.0	18.3	5.2	6.2	47.5	47.2	12.6	4.0	3.5
		(2,710/42)	(1,890/42)	(767/42)	(217/42)	(262/42)	(1,997/42)	(1,984/42)	(529/42)	(170/42)	(148/42.8)
	Total	56.9	43.5	14.0	5.2	5.3	32.8	37.0	9.5	3.7	3.9
		(4,270/75)	(3,266/75)	(1,049/75)	(391/74.9)	(395/75)	(2,457/74.9)	(2,774/75)	(708/74.9)	(278/74.6)	(296/75)
Tokyo	Well-implemented area	21.5	6.3	1.8	3.6	2.6	6.6	19.8	8.0	2.4	2.6
		(128/6)	(50/8)	(14/7.9)	(29/8)	(21/8)	(53/8)	(158/8)	(64/8)	(19/7.9)	(20/7.8)
	Implemented area	21.1	14.6	9.3	7.4	10.4	13.3	16.2	8.8	3.7	2.3
		(1,074/50.9)	(1,091/74.7)	(699/74.8)	(551/74.8)	(774/74.2)	(980/73.9)	(1,199/74.1)	(652/74.4)	(276/74.1)	(172/73.8)
	No-implementation area	43.5	18.8	13.4	11.2	12.5	21.8	40.5	12.3	5.4	4.6
		(3,952/90.9)	(3,347/177.6)	(2,376/177.2)	(1,969/175.5)	(2,208/176.5)	(3,850/176.8)	(7,169/177.2)	(2,187/177.3)	(951/177.4)	(802/174.7)
	Total	34.9	17.2	11.9	9.9	11.6	18.9	32.9	11.2	4.8	3.9
		(5,154/147.8)	(4,488/260.3)	(3,089/259.9)	(2,549/258.3)	(3,003/258.7)	(4,883/258.6)	(8,526/259.3)	(2,903/259.6)	(1,246/259.4)	(9,94/256.3)
Overall	Well-implemented area	31.8	18.4	5.0	3.4	3.0	10.7	20.4	5.7	2.8	3.3
		(795/25)	(498/27)	(134/26.9)	(93/27)	(82/27)	(289/27)	(552/27)	(153/26.8)	(76/26.9)	(88/26.7)
	Implemented area	30.3	22.8	9.7	7.5	9.6	13.7	18.1	8.4	3.7	2.9
		(1,967/64.9)	(2,019/88.7)	(861/88.8)	(661/88.7)	(846/88.2)	(1,204/87.8)	(1,595/88)	(742/88.4)	(327/87.7)	(252/87.2)
	No-implementation area	50.1	23.8	14.3	10.1	11.3	26.7	41.8	12.4	5.1	4.4
		(6,662/132.9)	(5,237/219.6)	(3,143/219.2)	(2,186/217.5)	(2,470/218.5)	(5,847/218.8)	(9,153/219.2)	(2,716/219.3)	(1,121/219.4)	(950/217.4)
	Total	42.3	23.1	12.4	8.8	10.2	22.0	33.8	10.8	4.6	3.9
		(9,424/222.8)	(7,754/335.3)	(4,138/334.9)	(2,940/333.2)	(3,398/333.7)	(7,340/333.5)	(11,300/334.3)	(3,611/334.5)	(1,524/334.1)	(1,290/331.3)

¹Number of sentinel sites did not become an integral number as the period for a sentinel site designated for shorter than a year was converted to yearly-based period.

Figure 1. Trend in the number of mumps cases per sentinel site, grouped by areas of different subsidization status. Well-implemented area: where the subsidization program was started before 2010; Implemented area: where the subsidization program was started after 2010, but before 2015; and No-implementation area: where no subsidization program was implemented before 2015.

Figure 2. Trend in the number of mumps cases per sentinel site, grouped by areas of different subsidization status in each prefecture. Well-implemented area: where the subsidization program was started before 2010; Implemented area: where the subsidization program was started after 2010, but before 2015; and No-implementation area: where no subsidization program was implemented before 2015.

3.4. Impact of the subsidization program on prevention of mumps

The yearly mean number of mumps cases per site and the crude reporting ratio during the 2015–2016 outbreak were summarized in Table 3. The mean number in the well-implemented and implemented areas tended to be smaller than the mean during the 2010–2011 outbreak, while there was no remarkable change in the no-implementation areas (24.1 ± 10.2 in well-implemented areas, 22.2 ± 19.2 in the implemented areas, and 37.9 ± 27.6 in the no-implementation areas during the 2010–2011 outbreak). While a similar finding was observed for Ibaraki (the 2015–2016 vs. the 2010–2011 outbreak in the well-implemented areas: 17.1 ± 4.6 vs. 29.8 ± 3.9, in the implemented areas: 19.3 ± 14.4 vs. 59.9 ± 25.4, and in the no-implemented areas: 46.8 ± 29.2 vs. 52.7 ± 27.6, respectively), there were no remarkable changes in Tokyo (the 2015–2016 vs. the 2010–2011 outbreak in the well-implemented areas: 13.2 vs. 12.7, in the implemented areas: 14.1 ± 10.7 vs. 16.0 ± 8.8, and in the no-implementation areas: 29.7 ± 13.6 vs. 31.4 ± 25.7, respectively). Finally, the adjusted model confirmed that the subsidization program implemented between 2010 and 2015 impacted on the number of mumps cases during the 2015–2016 outbreak with a decrease in the numbers (0.62, 95%CI = 0.52–0.73). The difference remained significant when the data was stratified by the prefectures, while level of the decrease was different between the prefectures (0.29, 95%CI = 0.21–0.42 for Ibaraki vs. 0.70, 95%CI = 0.57–0.86 for Tokyo). When excluding data from areas where the subsidization program has been implemented during the 2010–2011 outbreak, the result remained significant; we were unable to calculate the reporting ratio in Ibaraki as there were no areas in a category of the implemented area (data not shown).

Table 3. Impact of the subsidization program on prevention of mumps during the 2015–2016 outbreak

	Mumps cases per sentinel site during the 2015–2016 outbreak			Reporting ratio during the 2015–2016 outbreak ^1 (95%CI)
Subsidization category (N of area)	(yearly mean ± SD)			Crude	Adjusted
Overall
Well-implemented area (3)	15.8	±	3.9	0.45 (0.34–0.61)	−^2
Implemented area (14)	14.9	±	10.8	0.43 (0.37–0.49)	0.62 (0.52–0.73) *
No-implementation area (26)	35.0	±	20.7	(reference)	(reference)
Ibaraki
Well-implemented area (2)	17.1	±	4.6	0.36 (0.26–0.52)	−^2
Implemented area (2)	19.3	±	14.4	0.41 (0.30–0.57)	0.29 (0.21–0.42) *
No-implementation area (8)	46.8	±	29.2	(reference)	(re ference)
Tokyo
Well-implemented area (1)	13.2			0.44 (0.26–0.77)	−^2
Implemented area (12)	14.1	±	10.7	0.48 (0.40–0.57)	0.70 (0.57–0.86) **
No-implementation area (18)	29.7	±	13.6	(reference)	(reference)

¹Reporting ratio was calculated, using a Poisson regression model. For the adjusted model, the number of mumps cases per site during the 2010–2011 outbreak, population density, pediatric population, and a change of the pediatric population from 2010 to 2015 were controlled. ² Well-implemented areas were excluded for the analysis using the adjusted model, because it was assumed that most population had been already immunized at the 2010–2011 outbreak.

* P < 0.0001, ** P = 0.0006, N: number, SD: standard deviation, CI: confidential interval.

4. Discussion

For implementation of the local subsidization program for mumps, 26.2% of the local governments (456/1,739) were found to have subsidization programs in 2019. Compared to the previous surveys in 2010 (3.5%)¹⁹ and 2012 (11.0%),²⁰ the subsidization programs for mumps vaccines had expanded. The awareness of the importance of vaccines to prevent the diseases has increased in Japan in the last 10 years with the introduction of new vaccines around 2010, some of which have been implemented into the national universal vaccination program in 2013.²¹ Therefore, the changes might lead to an increase in the implementation of local subsidization programs for mumps. In this study, the extent of local subsidization program implementation was underestimated, because the survey was conducted through the website only. Some local governments may have implemented the subsidization program without posting it on their websites. In addition, some local governments did not implement a specific subsidization program for mumps; however, they distributed vouchers in exchange of which citizens could choose from several public services being offered, including the mumps vaccination.

The coverage of mumps vaccination may improve in the recent 10 years, when considering previous studies: a recent study in Tokyo revealed an increasing trend in the mumps vaccination coverage rate from 27.6% in 2012 to 61.8% in 2016;²² and another study estimated that the coverage rate of the 1st dose of mumps vaccination as 75.5% until the end of 2019.²³ However, as previous studies showed that more than 75–90% of the population should be immunized against mumps to prevent outbreaks,^24,25 the expansion of the local subsidization program may not be sufficient for mumps prevention; as revealed by the peak in the 2015–2016 outbreak (Figure 1). In addition, a previous study indicated that a necessity of mumps vaccination even when considering natural infection including asymptomatic infection.²⁶ Therefore, greater expansion of the subsidization program will be necessary for the prevention of mumps in the whole of Japan; this could be implemented as a national universal immunization program for mumps. Moreover, when considering the result that the peak was also observed during the 2015–2016 outbreak in both the well-implemented and implemented areas (Figure 1 and 2), the coverage of the current local subsidization program in the areas might not be sufficient enough for the prevention of mumps as there were several type of subsidization coverages and eligibilities (such as subsidization of full or partial expenses, or for both two doses or only one dose).

As the timing of outbreaks in the prefectures was same as the previous studies, infection status in the prefectures could be representative to the whole of Japan. The number of mumps cases per sentinel site in areas of subsidization, tended to be low compared to that in the no-implementation areas throughout the data period (Figure 1). Although the analysis was descriptive, we could consider that the subsidization program supported the prevention. However, considering that the implemented areas were where the subsidization program was implemented between 2010 and 2015, the number of mumps cases per sentinel site during the 2010–2011 outbreak should be similar to that in the no-implementation areas, thereafter decrease to the similar level of that in the well-implemented areas. As the difference in the trend was apparent between Tokyo and Ibaraki (Figure 2), more area-specific factors and background should be considered to conclude the impact of the program. For example, when a major reason to implement the subsidization program is to prevent the disease, it is reasonable that the program is implemented in areas where the number of pediatrics is high. However, as considering that areas where the population density was high and where the pediatric population was not necessarily high tended to be subsidized in Tokyo, the reason might be different such as to reduce in healthcare cost or to enhance the appeal of fulfilling welfare program. In addition, a started year of the subsidization program differed among Tokyo and Ibaraki. In Tokyo, the started year in major areas categorized in the implemented area was 2010, while in Ibaraki the year was no earlier than 2011. Especially considering the mumps outbreak occurred during 2010 and 2011, people might have more incentive to receive the vaccine through the program, leading to a rapid increase in mumps vaccination. A difference in the started year in the well-implemented area (2007 in Tokyo vs. earlier than 2000 in majority in Ibaraki) might also represent the difference observed during the 2010–2011 outbreak. As there was only one area (administrative district) categorized in the well-implemented area in Tokyo, specific factors to the given area might impact on the trend. Therefore, as we could not consider the factors sufficiently in the study, the result should be implied with the limitations above. There was also a design-based limitation: a misclassification of the subsidization status could occur when the status was different between administrative districts in the same healthcare-based area.

The adjusted Poisson regression model showed that the subsidization implemented between 2010 and 2015 decreased number of mumps cases during the 2015–2016 outbreak (Table 3). As the significant difference remained when data was stratified by the prefectures, it could be considered that the impact of the subsidization was positive in both urban and suburban areas. However, we should consider that there are several another factors, been associated with the outbreak including such as socioeconomics, geographical aspect, exposure settings, intensity and duration of close contact, age and compromised immunity,²⁷ which we did not include in the model.

The biggest limitation of the study was missing information on data regarding vaccination coverage. There was no available data that indicated how many people in subsidization areas were vaccinated, or whether people in the non-subsidization areas were vaccinated. We were also unable to assess a direct association between the subsidization programs and distribution of mumps vaccinations because the distribution data was not disclosed by the prefectures nor was its area based. However, the data supported a possibility of increase of mumps vaccination coverage as number of distributed mumps vaccines expanded from 738 thousand doses in 2010 or 757 thousand doses in 2012 to 1,168 thousand doses in 2018.²⁸ For a more comprehensive view, a system that captures vaccine recipients with a record of vaccinations such as a vaccine registry will be necessary.

Conclusion

The local subsidization programs have expanded, especially during the last 10 years, and they have supported a decrease in the mump incidence during the 2015–2016 outbreak in Japan. To effectively control mumps, a further expansion of the subsidization program will be necessary. It is also recommended that further studies with detailed data including vaccination coverage should be conducted.

Disclosure of potential conflicts of interest

MM is also an employee of a pharmaceutical company, MSDKK. However, he has no conflicts of interest directly relevant to the content of this study as MSDKK is not a marketing authorization holder of mumps vaccine. TO and NM have no conflicts of interest directly relevant to the content of this study.

Ethical consideration

This study was conducted in accordance with the Ethical Guidelines for Medical and Health Research Involving Human Subjects, issued on 28 Feb 2017 by the regulatory agency in Japan.²⁹ According to the guideline, no ethical approval was required for the protocol as we only used publicly available information which had already been unlinked and anonymized.

Acknowledgments

We would like to thank Elsevier Author services for English editing.

Additional information

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.