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The topic of This Month Vol.38 No.3(No.445)

Measles in Japan, 2016

(IASR Vol. 38 p45-47: March, 2017)

Measles is a highly transmissible acute systemic infectious disease caused by measles virus.  Its transmission mode is airborne, droplet or contact.  Main clinical manifestations are fever, rash and catarrh.  Approximately 40% of the patients require hospitalized treatment.  Complications such as pneumonia or encephalitis may lead to death.  In 2015, an estimated 134,200 people, mainly children in developing countries, died of measles [World Health Organization (WHO) fact sheet, November 2016, http://who.int/mediacentre/factsheets/fs286/en/].

As Measles vaccine is safe and effective, WHO and others have been working to achieve measles elimination globally. Measles elimination is defined as “the absence of endemic measles transmission in a defined geographical area (e.g. region or country) for ≥12 months in the presence of a well-performing surveillance system”. The Global Vaccine Action Plan adopted at the 65th World Health Assembly in 2012 aims for the elimination of measles and rubella in five of the six WHO regions by 2020. In 2007, Japan produced the “Guidelines for the prevention of specific infectious diseases: measles and other designated infections” (notice on December 28, 2007, modified on February 3, 2016). The WHO Western Pacific Regional Verification Commission for Measles Elimination verified Japan as having achieved “measles elimination” status in March 2015, and this status has been maintained to date.

National Epidemiological Surveillance of Infectious Diseases (NESID): Measles is a category V infectious disease that requires notification of all diagnosed cases (see http://www.niid.go.jp/niid/images/iasr/35/410/de4101.pdf for notification criteria and definitions used for the types of diagnosis). The reported number of measles cases in 2015 was 35, the lowest since 2008 when 11,013 cases were reported (as of February 1, 2017) (Fig. 1). In 2016, however, due to outbreaks such as those that occurred in Matsudo-City (IASR 37: 234-235, 2016), Kansai International Airport (see pp. 48 and 49 of this issue), and Amagasaki-City (see p. 51 of this issue), the number of cases increased starting in week 33 (mid-August), and a total of 165 cases were eventually reported. At the prefecture level, Osaka (51 cases), Chiba (25 cases), Tokyo (22 cases), Hyogo (20 cases), Saitama (8 cases), and Kanagawa (8 cases) reported the largest number of cases.

Among the notified cases, the proportion of laboratory-confirmed was only 38% in 2008, but increased to 94-95% since 2014 (Fig. 2). The proportion of modified measles* cases among the notified cases has been increasing (16% in 2014, 23% in 2015 and 32% in 2016).

As shown in Fig. 3 in p. 47, since 2009, the proportion of cases aged 10-19 years decreased first, which was followed by a decrease in cases aged 1-4 years, leading to an increase in the proportion of adult cases (≥20 years of age), with ≥70% of the cases being adults since 2015 (percentage of adults was 33% in 2008, 36% in 2009, 37% in 2010, 48% in 2011, 58% in 2012, 69% in 2013, 48% in 2014, 71% in 2015 and 72% in 2016). In 2016, among 165 cases, 60 cases were in their 20’s, 35 cases in their 30’s and 32 cases younger than 10 years.

In 2008-2016, 27-52% of the cases had unknown vaccination history (Table 1). In 2016, among a total of 165 cases notified (including 8 infants under the vaccine eligible age of <1 year), 47 cases (including 7 infants <1 year of age) were unvaccinated (28%), 40 cases vaccinated once (24%), 25 cases vaccinated twice (15%) and 53 cases had unknown vaccination history (including an infant <1 year of age) (32%). Among the 157 cases confirmed by laboratory diagnosis, 105 cases exhibited fever, characteristic rash, and catarrhal symptoms; among them, 43 (including 6 infants <1 year of age) were unvaccinated (41%), 21 were vaccinated once (20%), 7 were vaccinated twice (7%) and 34 including one infant <1 year of age had unknown vaccination history (32%). Among the 52 modified measles cases (no cases <1 year of age), characterized by atypical manifestations such as low grade fever and/or localized rash, three were unvaccinated (6%), 19 were vaccinated once (37%), 15 were vaccinated twice (29%), and 15 had unknown vaccination history (29%). These clinically milder modified measles cases included fewer unvaccinated cases. Those in their 20’s made up the largest proportion of the cases, but this age group had the largest number of modified measles cases and those vaccinated twice (Fig. 4).

Emergency school closure due to measles has not been reported since the temporary closure of a primary school in February 2014 (http://www.niid.go.jp/niid/ja/hassei/5339-measles-school-rireki.html).

Isolation and detection of measles virus: In 2016, prefectural and municipal public health institutes (PHIs) detected/isolated measles from 139 cases (Table 2). Among them, 35 cases (25%) had travelled abroad. Genotype D8 was detected from 66 patients (16 had travelled to Indonesia) during August-October, H1 from 57 patients (travelled to China and Mongolia for 2 each) mostly in August, and B3 from one patient in March (Table 2 & http://www.niid.go.jp/niid/images/iasr/rapid/meas/150811/masin1e_170125.gif). Fifteen cases could not be genotyped. The aforementioned genotypes include those not infected overseas but linked to international airports in Japan (IASR 37: 236-237, 2016) (see pp. 48 and 52 of this issue).

Current laboratory diagnosis practice (see p. 55 of this issue): To ensure that the measles transmission does not exceed 12 months (a criterion for maintaining measles elimination status), specimens from ≥80% of outbreaks need to be genotyped. In 2016, among 165 measles cases, 157 cases were laboratory-confirmed and 139 cases genotyped. In 2016, 85% of all laboratory-confirmed cases were diagnosed by real-time RT-PCR. In the revised version of the “Pathogen Detection Manual” for measles, in order to minimize potential cross contamination from PCR products, the real-time PCR methodology was incorporated (http://www.niid.go.jp/niid/images/lab-manual/Measles.V3.3.20150814.pdf). However, for specimens testing positive by real-time RT-PCR, they must be analyzed by nested RT-PCR for genotyping.

Vaccination coverage: Since FY2006, the routine immunization program in Japan has adopted the measles-rubella (MR) combined vaccine. The vaccination schedule consists of the first vaccination at 1 year of age and the second vaccination within one year before primary school entry. In FY2015, the vaccination coverage for the 1st dose was 96.2% and 92.9% for the 2nd dose. The coverage has been ≥95% for the past 6 years for the 1st dose. While coverage for the 2nd dose has been ≥90% for the past 8 years, it has not reached the targeted 95% (http://www.mhlw.go.jp/bunya/kenkou/kekkaku-kansenshou21/hashika.html).

National Epidemiological Surveillance of Vaccine-Preventable Diseases: In FY2016, 23 prefectures conducted the seroprevalence survey for measles (n=6,462) using the gelatine particle agglutination (PA) assay. Blood specimens were collected from mostly healthy subjects who donated blood or had a routine health exam (see p. 54 of this issue). The antibody positivity (PA antibody titre ≥1:16) among this population ≥2 years old has been ≥95% since FY2011 (Fig. 5).

Further measures to be taken: While Japan’s current status satisfies the condition of “measles elimination”, measles is endemic in many countries overseas (see pp.53, 58 and 59 of this issue). In 2016 alone, 24,000,000 foreigners visited Japan and 16,000,000 Japanese went abroad. Under such conditions, importation of measles from abroad is inevitable. The delayed diagnosis of the earlier cases led to several large measles outbreaks in Japan in 2016 (see p. 48 of this issue). To maintain “measles elimination status”, Japan should be equipped with systems that can prevent further spread following importation of measles. In order to do so, the following are deemed to be important: 1) to maintain coverage of the 1st and 2nd doses of MR vaccine at 95% or higher to maintain a high antibody positive level; 2) to strengthen surveillance for rapid detection and response to prevent further spread; and 3) to increase uptake of vaccination among people who come in contact with a large number of persons, such as healthcare workers, those who work at schools and childcare, staff at airports and other ports of entry, and for those going abroad (see pp. 48 and 56 of this issue).

Copyright 1998 National Institute of Infectious Diseases, Japan

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