Validity of measles immunization certificates submitted upon enrollment in an elementary school in Korea

Measles Elimination Activities in the Western Pacific Region: Experience from the Republic of Korea

We describe the global status of measles control and elimination, including surveillance and vaccination coverage data provided by the World Health Organization (WHO). Since 2000, two doses of measles vaccine (MCV2) became recommended globally and the achievement of high vaccination coverage has led to dramatic decrease in the measles incidence. Our finding indicates that, in the Western Pacific Region (WPR), substantial progress has been made to control measles transmission in some countries; however, the measles virus continues to circulate, causing outbreaks. The Republic of Korea (ROK) experienced a series of resurgence of measles due to the importation and healthcare-associated transmission in infants, however overall incidence and surveillance indicators met the WHO criteria for measles elimination. The ROK was verified to be measles-free along with Australia, Mongolia, and Macau, China in 2014. One of the effective elimination activities was the establishment of solid keep-up vaccination system in school settings. The lessons learnt from the measles elimination activities in Korea may contribute to enhancing the surveillance schemes and strengthening of vaccination programs in member countries and areas of WPR.

Reemergence of measles in South Korea: implications for immunization and surveillance programs

Following the implementation of the national measles elimination program, the Republic of Korea declared in 2006 that measles had been eliminated. However in 2011, a measles outbreak was reported in Gyeongnam Province in the southeastern part of the country. We conducted active case-based surveillance and analyzed the data of cases reported in 2011 to identify the factors contributing to the reemergence of measles in this province. Of 41 confirmed measles cases reported in Korea, 32 were from within the Gyeongnam Province. Among cases identified in the outbreak, 97% had inadequate history of immunization, 28% were not immunized at the recommended ages, and 22% were infants aged 6-11 months. The outbreak involved transmission in 3 hospitals, 1 kindergarten, 1 day-care center, and 3 households. Molecular analysis of measles virus isolates from 11 cases revealed the same D9 genotype, which was the first to be discovered in Korea. In conclusion, inadequate immunization coverage, non-timely immunization, infants under 12 months of age, nosocomial transmission, and international importation may play important roles in the reemergence of measles in Korea during the attempted sustained elimination of the disease.

Seroprevalence of measles among children affected by national measles elimination program in Korea, 2010

BACKGROUND

Following the implementation of national measles elimination plan in Korea, the elimination was declared in 2006. In order to sustain the elimination, high population immunity should be continuously monitored. To evaluate the current age-related susceptibility within the Korean population, we conducted the seroprevalence in children and adolescents who were affected by the national measles elimination plan.

METHODS

We used residual serum specimens to measure measles specific IgG and geometric mean titer (GMT) in birth cohorts 2007-2008 and 1997-2003. Among birth cohorts, 2007-2008 cohorts were grouped to evaluate the timeliness of first dose of MMR, 1994-2003 cohorts were grouped to evaluate the effect of keep-up MMR2 campaign, and 1992-1993 cohorts were grouped to evaluate the effect of catch-up campaign in 2001.

RESULTS

Overall, measles seropositivity rate was 86%. The highest seroprevalence of measles IgG was in birth cohorts 2007-2008. Measles seropositivity declined continuously in age groups. The birth cohorts 1994-1996 showed significantly lower levels of seropositivity and GMT than did the other birth cohorts.

CONCLUSION

Despite efforts to eliminate measles for the past 10 years in Korea, our study revealed specific birth cohorts remaining at risk for transmission. The adolescents born during 1994-1996 had the lowest measles seropositivity levels, and might represent a 'pocket' that has potential at increased risk for measles transmission. Further discussion for follow-up immunization should be placed for consideration in the near future.

Effectiveness assessment of vaccination policy against measles epidemic in Japan using an age-time two-dimensional mathematical model

OBJECTIVES

In 2007, measles prevailed among the youth and young adult population in Japan, creating in a serious social problem. Among the developed countries, Japan has a relatively high incidence of measles. The objective of this study was to assess the effect of improvements in the vaccination policy against measles through simulations.

METHODS

We developed an age-time two-dimensional model for the transmission of measles to reflect an age structure, enabling contact rate to be selected by age. Introduction of the maternal immunity class into the model allowed natural infection and vaccination to be discriminated along the course of an infant's mother acquiring the immunity, thereby resulting in an improved accuracy of the simulations in infants. Several vaccination scenarios were attempted in order to assess the influence of various vaccination policies on the prevention of a measles epidemic.

RESULTS

The results of this quantitative study indicated that suppression of a measles outbreak requires the maintenance of high vaccine coverage and that a decline in vaccine coverage may result in a measles epidemic.

CONCLUSIONS

The present standard immunization program for measles will maintain an acceptable level of immunity and is therefore associated with a low risk of an epidemic after discontinuation of the third and fourth stages as scheduled--as long as at least 90% vaccine coverage of the first and second is maintained. The simulation results show that discontinuation of the third and fourth stages of vaccination as scheduled should be accompanied by endeavors to maintain appropriate high vaccine coverage of the first and second stages.