An Outbreak of Measles in a University in Korea, 2014.

Measles has been declared eliminated from the Korea since 2006. In April 2014, a measles outbreak occurred at a University in Seoul. A total of 85 measles cases were identified. In order to estimate vaccine effectiveness of measles vaccine, we reviewed the vaccination records of the university students. The vaccine effectiveness of two doses of measles containing vaccine was 60.0% (95% CI, 38.2-74.1; P < 0.05). Transmission was interrupted after the introduction of outbreak-response immunization. The outbreak shows that pockets of under-immunity among college students may have facilitated the disease transmission despite the high 2-dose vaccination coverage in the community.

An increasing, potentially measles-susceptible population over time after vaccination in Korea.

BACKGROUND: In Korea, measles occurs mainly in infants <12months of age, who are unvaccinated. In addition, vaccine populations, including adolescents and young adults, can become infected though importation. Thus, the question arises whether the current level of herd immunity in Korea is now insufficient for protecting against measles infection. METHODS: Age-specific measles seroprevalence was evaluated by performing enzyme immunoassays and plaque reduction-neutralization tests on 3050 subjects aged 0-50years (birth cohort 1964-2014) and 480 subjects aged 2-30years (birth cohort 1984-2012). RESULTS: The overall seropositivity and measles antibody concentrations were 71.5% and 1366mIU/mL, respectively. Progressive decline in antibody levels and seropositivity were observed over time after vaccination in infants, adolescents, and young adults. The accumulation of potentially susceptible individuals in the population was confirmed by comparing data from 2010 and 2014 seroprevalence surveys. The statistical correlation between measles incidence and measles seronegativity was determined. CONCLUSIONS: Waning levels of measles antibodies with increasing time post-vaccination suggests that measles susceptibility is potentially increasing in Korea. This trend may be related to limitations of vaccine-induced immunity in the absence of natural boosting by the wild virus, compared to naturally acquired immunity triggered by measles infection. This study provides an important view into the current measles herd immunity in Korea.

Trend of measles, mumps, and rubella incidence following the measles-rubella catch up vaccination in the Republic of Korea, 2001.

Following the introduction of measles-rubella (MR) catch-up vaccination in 2001 and two dose measles-mumps-rubella (MMR2) keep-up program in 2002, the incidence of measles, mumps, and rubella was not evaluated systematically. To describe the recent changes in epidemiology, a population-based incidence study from 2001 to 2015 using national notifiable disease surveillance data was conducted. Between 2001 and 2015, there was decrease in the incidence of measles and rubella, whereas a steady increase in mump incidence was noted. The age distribution of mumps cases has shifted to the older age group, whereas rubella became more frequent in younger age group. The incidence of mumps showed an increase in every birth cohorts, except for the decrease in incidence for catch-up vaccination cohort from 131 cases in 2007-2011 to 64 cases per 100 000 in 2012-2015. Continuing in monitoring of mumps and strengthening of the high two-dose MMR vaccination coverage should be taken place in Korea.

How Can We Identify the Elimination of Infectious Diseases? Experience From an Active Measles Laboratory Surveillance System in the Republic of Korea.

Global efforts have markedly decreased the disease burden of vaccine-preventable diseases. Many countries have made considerable progress toward the elimination of measles. As elimination is approached, the very low incidence achieved by high vaccination coverage has underscored the need for a sensitive and timely surveillance system. In the Republic of Korea, an active laboratory surveillance system (ALSS) was implemented to supplement the existing passive surveillance system in 2006. The ALSS connects 5 major commercial laboratories and the national measles reference laboratory, where referred samples with positive or equivocal results are retested. Annually, from 2009 to 2013, 3714 suspected cases were detected through the ALSS, an expansion of 8- to 57-fold, compared with only the passive surveillance system. The ALSS, with its sensitivity and timeliness, is a reasonable strategy to supplement the existing measles surveillance system and to help identify the elimination of measles.

Resurgence of measles in a country of elimination: interim assessment and current control measures in the Republic of Korea in early 2014.

Since the beginning of 2014, the Republic of Korea has experienced a resurgence of measles cases. Among the 220 cases confirmed as measles during epidemiological weeks 1-20 (December 29, 2013 to May 17, 2014), 10 imported cases were identified. The predominant genotype was B3, which reflects the circulating measles virus in adjacent countries. Even with the verification of measles elimination in March 2014 by the World Health Organization, recent importation has been related to international travel. Targeted control measures have been implemented in addition to proper isolation and patient care. A vigilant surveillance system and high levels of vaccine coverage should be maintained to sustain the measles elimination status.