Japan formerly used the one dose measles vaccine for routine immunization to children 12-90 months after birth. In 2006, the vaccination schedule was revised and measles-rubella combined vaccine was introduced. Now the target age of the first vaccination is one year, and that of the second vaccination is one year preceding primary school entrance (5-6 years of age). Namely, two doses of measles-containing vaccine (MCV) are required before entrance to the primary school (IASR 27: 85-86, 2006). In addition, in 2007, in response to the outbreak of measles among young populations in their 10s and 20s (IASR 28: 239-240, 2007), vaccination to the first grade students of the junior high school (12-13 years of age) and those aged 17-18 years (including the third grade students of the high school) were added as five-year temporal measures under the Preventive Vaccination Law so as to increase the immunity level among this population.
The measles case reporting in compliance with the Infectious Diseases Control Law was also changed to notification of all cases in January 2008 (IASR 29: 179-181 & 189-190, 2008). In the former sentinel surveillance of measles, the sentinel clinics and hospitals reported clinically diagnosed cases since the National Epidemiological Surveillance of Infectious Diseases (NESID) started in July 1981. But, the doctors are now under an obligation of reporting measles cases together with clinical diagnosis and, where possible, laboratory data to the nearby health center. On account of their recent increase among the people received one dose of MCV, the “modified measles” cases that failed to exhibit the typical symptoms are requested to be reported if they are confirmed by the laboratory diagnosis (information of measles is found in http://idsc.nih.go.jp/disease/measles/index.html).
Measles incidence under the NESID: During weeks 1-52 of 2008, total 11,007 cases, 4,200 cases based on laboratory diagnosis (including 1,024 “modified” measles cases) and 6,807 cases based on clinical diagnosis, were reported (as of January 21, 2009). In 2008, measles increased suddenly in week 5 and maintained its high incidence level for more than 20 weeks. There were two peaks, one in week 7 (567 cases) and the other in week 17 (543 cases). It subsided gradually and became less than 50 cases after week 32, but more than 10 cases continued to be reported every week up to the week 52 (Fig. 1).
The male cases dominated the female cases in number (6,426 for male vs. 4,581 for female). In the age distribution, there were two peaks, 0-1 year and 15-16 years. More than 200 cases were reported for each age of 0-1 year and 8-27 years (Fig. 2). 4,910 cases had no vaccination history, 2,933 had received one dose, and 131 two doses. The vaccine history of the remaining 3,033 was unknown. Most 0-year-old cases had no vaccination at all (see p. 31 of this issue).
When prefectures were compared for the incidence of measles, Kanagawa (3,558), Hokkaido (1,460), Tokyo (1,174) and Chiba (1,071) were the top four. The measles cases reported in the metropolitan area, Kanagawa, Tokyo, Chiba and Saitama (388) combined, accounted for 56% of the total. The other prefectures where more than 100 cases were reported were Fukuoka, Osaka, Shizuoka, Aichi, Kyoto, Akita, Hyogo, Hiroshima, and Okayama (Fig. 3).
As for complications, nine measles encephalitis cases (all were ≥10 years) were reported in 2008 (the same number as in 2007).
School outbreaks: From April 6 to July 19 in 2008, there were 64 temporary closures of a school, 45 temporary closures of the same year classes, and 14 temporary closures of a class or classes, amounting to 123 partial or total closures of schools reported to the Ministry of Health Labour and Welfare (MHLW). The number was about one third of that in the same period of 2007 (363). The highest number of the closures was in high schools (59), followed by junior high schools (27), primary schools (14) and universities/colleges (11) (http://idsc.nih.go.jp/idwr/kanja/measreport/meas08/meas08-15.pdf).
Situations of epidemics in different prefectures in 2008: In the prefectures which experienced larger number of measles cases in 2008, measles epidemics had already started in 2007 (IASR 29: 128-129, 2008). Akita Prefecture experienced a sudden surge of measles in week 51, and the local government temporarily suspended unimmunized children from school to prevent further spread of the infection (IASR 29: 102-103, 2008). Chiba Prefecture experienced two outbreaks, the first one in primary and junior high schools in weeks 5-12 and the second one in high schools and in the local communities in weeks 21-29; the latter was triggered by studentsf participation in the High School Judo Championship (see p. 32 of this issue). Okinawa Prefecture experienced two outbreaks caused by measles brought into the island from outside in occasions of a live concert in March and an outdoor barbecue in August (see p. 34 of this issue).
Isolation and detection of measles virus: Measles virus has 8 clades from A to H, and 23 genotypes. In Japan, the epidemic of 2001 was caused by D5. In 2002-2003, H1 became predominant (IASR 25: 60-61, 2004). Since 2006, D5 has been circulating (http://idsc.nih.go.jp/iasr/measles-e.html). From January to December of 2008, 27 prefectural and municipal public health institutes (PHIs) in the metropolis and 21 prefectures isolated or detected 264 measles viruses (as of January 22, 2009). Among 188 strains genotyped, 175 were D5. The remaining 13 consisted of 5 strains of H1 obtained from 3 and 2 domestic cases in Osaka in March (IASR 29: 160-161, 2008) and Chiba in May, respectively, one strain of D4 from a case in Osaka in May who came back from Israel and developed symptoms 3 days later (see p. 39 of this issue), and 7 strains of A (vaccine type) from vaccinees within 3 weeks after vaccination.
The National Epidemiological Surveillance of Vaccine-Preventable Diseases: Antibody positives are defined as those having measles antibody titer higher than 1:16 in the gelatin particle agglutination assay (PA). However, it is considered that antibody titer ≥1:128 is necessary for protection from measles (see p. 40 of this issue). In 2008, only 51% of one-year-old children were antibody positive (≥1:128) (Fig. 4). Among 5-7-years children, antibody positive rate exceeded 95%, which was high reflecting the second vaccination that started in 2006. The antibody positive rate increased in 12-year-old and 17-year-old age groups, reflecting the second vaccination temporarily introduced in 2008. Generally, however, among 10s, especially at 10 and 15 years the antibody positive rate was low, and, even among age groups above twenty, there were many people possessing antibody titer below 1:128.
Vaccination rate: The second vaccination rate (% of the target age population) in the first half of 2008 fiscal year in Japan was 51% for 5-6 years, 56% for 12-13 years and 48% for 17-18 years (as of the end of September) (see p. 43 of this issue). Among prefectures, Fukui was the highest in the vaccination rate, 67%, 84% and 73% for the three respective target ages. The prefectures with the lowest coverage for three target cohorts were Miyazaki (40%), Osaka (44%) and Tokyo (32%), respectively (http://www.mhlw.go.jp/bunya/kenkou/kekkaku-kansenshou21/index.html). Fukui Prefecture has established a system to identify unvaccinated persons, and has advised the unvaccinated persons individually to receive vaccination (IASR, 29: 191-193, 2008). In Hamamatsu City, the high second vaccination rates for 12-13 years (75%) and 17-18 years (72%) were attained by promoting vaccination in cooperation with the school nurses in junior high and high schools (see p. 44 of this issue).
Further measures needed in future: For attaining measles elimination, further increase of the vaccine coverage is necessary. For eliminating measles in 0-year infants, there is no other means than total elimination of measles from Japan (see p. 31 of this issue). For the people of the three target cohorts, the second vaccination is to be covered by public expense till the end of March in this year, but thereafter from April 1 it has to be covered by private expense. Therefore, unvaccinated persons are advised to receive vaccination before the end of this fiscal year. During the Childrenfs Immunization Week from February 28 (Saturday) to March 8 (Sunday), in some areas, doctors will open the consultation room in holidays or in evenings for vaccination.
The Special Infectious Disease Prevention Guidelines on Measles (MHLW, December 28, 2007) requests laboratory diagnosis for all the measles cases once the measles case number is reduced to a certain level. In June 2008, PHIs and National Institute of Infectious Diseases agreed to establish the Measles-Rubella Reference Centers as a collaborative mechanism and revised the Measles Laboratory Diagnosis Manual (http://www.nih.go.jp/niid/reference/measle-manual-2.pdf) to enforce the laboratory diagnosis practice (see p. 45 of this issue). On January 15, 2009, MHLW sent a correspondence “Strengthening the Framework of Measles Laboratory Diagnosis” to the local governments (see p. 47 of this issue). Definitive diagnosis assisted by the laboratory diagnosis is indispensable for preventing the spread of measles in the community, particularly when we encounter the possible first case whose contact source is unclear.