The importance of adult pertussis vaccination was emphasized in countries with high primary childhood vaccination rates after pertussis outbreaks in adults since the 1990s. The source of infections in infants less than 1 year of age with insufficient vaccine-induced immunity was determined to be adults. The US Advisory Committee on Immunization Practices emphasized the need for adult Tdap vaccinations for pregnant women in particular and recommended Tdap vaccination at 27-36 weeks of pregnancy regardless of the previous Td/Tdap vaccination history [5]. Whereas approximately 20 cases of pertussis have been reported in Korea each year since 2001, this number increased to 66 in 2009 and 97 in 2011 [6], followed by a 2012 outbreak of 230 cases reported especially in middle and high schools in the Jeollanam-do region [7]. Nevertheless, the Tdap vaccination rate in Korea is extremely low in both adults and women of fertile age, and awareness of the Tdap vaccine is also low [8]. Vaccination history should be used to determine whether citizens of countries with active childhood and adult vaccination programs such as the US and developed countries in Europe should be vaccinated. However, proactive Tdap vaccination could be considered for adults with uncertain primary vaccination history in countries without active childhood vaccination programs. In particular, in countries with large numbers of citizens residing in Korea, including China, Indonesia, Uzbekistan, and Mongolia, the DTP booster administered at 4-6 years of age does not contain pertussis [9]. The KSID recently revised its recommendations that pregnant women can be vaccinated with the Tdap vaccine [10]. However, the current incidence in Korea does not meet the level of evidence necessary for required vaccination with every pregnancy, as recommended by the Advisory Committee on Immunization Practices. Based on the benefits and safety of vaccination during pregnancy, a single vaccination is recommended before pregnancy for women planning a pregnancy; meanwhile, for those not vaccinated prior to pregnancy, the recommendation is to vaccinate at 27-36 weeks of pregnancy, identical to recommendations for the immigrant population.

Approximately 1,400,000 individuals are infected with the hepatitis A virus annually, and the incidence is closely related to socioeconomic, health, and sanitation levels [11]. The disease mostly occurs in children in less developed countries, but the overall prevalence is low in countries with good sanitation. Because the rate of naturally acquired immunity in adults is low, sporadic outbreaks occur mostly in adults. The sanitary level in Korea improved considerably after the 1970s; after introduction of the vaccine in 1997, Korea has progressed toward becoming an epidemiologically low-risk region. Although there were 105 cases in 2001, the number increased significantly in 2006 to 1937. Most of the infected patients were in their 20s and 30s [11]. With active vaccination campaigns, the number of new patients reported each year is gradually decreasing, with 5,521, 1,197, and 867 in cases reported in 2011, 2012, and 2013, respectively [12]. However, vaccination is recommended in adults without immunity to reduce the risk of sporadic transmission in these individuals. The seroprevalence of hepatitis A antibody in adult foreigners differs according to country or origin and age group (Table 1). Generally, the seroprevalence of citizens of developed countries such as the US, Australia, and Western European countries is low, whereas that of citizens of less developed countries is high because of natural infection [13]. Therefore, the history of hepatitis A infection should be considered before vaccination. In some countries, the hepatitis A vaccine is included in the childhood vaccination schedule. For example, in China, which accounts for half of all foreigners residing in Korea, all children are vaccinated once at 18 months of age. However, countries such as the US, Japan, and Vietnam do not include the hepatitis A vaccine in their childhood vaccination schedules [14]. Because the situation is different for each country, it is recommended that IgG seropositivity against hepatitis A be assessed prior to vaccination, when possible.

Since 2001, children entering school in Korea have been required to submit a vaccination certificate confirming administration of the second dose of the MMR vaccine. Since 2006, measles has been managed at an eradication level [15], and in 2014, the World Health Organization recognized that Korea had eradicated measles. However, a measles outbreak in East Asian countries such as the Philippines and Vietnam in 2014 resulted in an increased number of imported measles cases in Korea as a result of secondary spread in schools. Several countries are currently conducting vaccination projects to eradicate measles, aiming for a completion rate exceeding 95% for the two-dose MMR vaccination. However, actual vaccination rates vary significantly among different regions. In daveloped countries in Europe, Asia, and the Americas, two doses of the MMR vaccine are recommended, and the vaccination rate is relatively high [16]. However, although MMR vaccination is performed in less developed and developing countries in the Middle East and Asia, administration of two doses of the MMR vaccine is uncommon. The majority of countries in Africa use a measles vaccine instead of the MMR to vaccinate children once at 9 months of age, and the vaccination rate is considered low [1718]. Accordingly, the number of doses of the MMR vaccine should be checked; when it is not clear whether individuals have received two doses of the vaccine, an additional dose of the MMR vaccine is believed to be effective, with reference to the circumstances in each country and region. It is important to test for rubella antibody before pregnancy in women of reproductive age; if the woman is seronegative, a single dose of the MMR vaccine should be given to prevent rubella.

Compared to other vaccines, few countries worldwide regularly administer the varicella vaccine, likely because varicella infections at a young age are not generally accompanied by major complications. Nevertheless, in countries in which vaccination is not performed, varicella can become an additional burden on society and families because outbreaks at day-care facilities can require home treatment of infected children and temporary closure of facilities to control outbreaks. For this reason, approximately 15 countries worldwide, including Korea, recommend varicella vaccination as part of their national vaccination programs (Table 2). Currently, in countries in North America and Germany, administration of the second dose at 4-6 years of age is mandatory because of varicella outbreaks in school-aged children because of breakthrough infections. In Australia, the decision to administer a second dose to children is left up to parents, and there is an ongoing debate regarding whether the second dose should become mandatory in the future [19]. In Japan, vaccines included in the national vaccination programs are divided into required and optional. Because the varicella vaccine is classified as optional, the cost of vaccination is not supported by the government. The varicella vaccination rate in Japan is an estimated to be 20-40% based on vaccine shipment data [20].

It is recommended that foreigners residing in Korea should also be vaccinated based on their age and immunity at the time of immigration. It is appropriate for foreigners in Korea to follow the same schedule as Korean children and receive vaccinations at 12-15 months of age, whereas older individuals should receive catch-up vaccinations. Because childhood varicella vaccination rates and seroprevalence differ by country, it is recommended that foreigners residing domestically be tested for varicella antibodies prior to vaccination.

The risk of Japanese encephalitis is generally low when people residing in non-endemic regions travel to endemic areas; the risk of infection for travelers to Asia is less than 1 in 1,000,000. Between 1973 and 2008, a total of 55 patients reportedly contracted Japanese encephalitis while travelling [2122]. The main countries in which infection occurred were Thailand, Indonesia, China, and the Philippines, and there are no cases of infection in foreigners in Korea after travel. However, between 2000 and 2012, 82 cases of Japanese encephalitis were reported in Korea [23]. As foreigners travelling to endemic regions have a similar risk as Korean residents, vaccination is recommended. Among patients who contract Japanese encephalitis after visiting an endemic area, 65% stayed for more than 1 month; when the duration of travel was short, 80% were infected outside of urban regions [24]. Based on this finding, the recommendations state that individuals staying in Korea longer than 1 month, as well as those staying for less than 1 month but who are planning a trip outside of urban areas, should undergo vaccination. The majority of cases of Japanese encephalitis occur between August and November in Korea, and it is recommended to undergo vaccination during this period [24].

Japanese encephalitis vaccination is mandatory among the following countries with Japanese encephalitis: South Korea, Japan, China, Taiwan, Hong Kong, and Thailand [924]. Vaccination is recommended for foreigners entering Korea from countries without Japanese encephalitis and for citizens of countries with mandatory vaccination policies without vaccine immunity who satisfy the criteria of the recommendations.

Only inactivated vaccines may be administered to adults, and there are three types of inactivated vaccines used globally (mouse brain-derived, hamster kidney-derived, and Vero cell-derived). Two inactivated vaccines are currently used in Korea: the mouse brain-derived Nakayama strain and the Vero cell-derived Beijing strain. However, in Western countries, including the US, only the inactivated Vero cell-derived SA 14-14-2 strain vaccine is used. Therefore, for foreigners with vaccine-based immunity to Japanese encephalitis who want a booster vaccination, the type of vaccine previously administered must be confirmed. An experimental study illustrated that a single booster dose with the inactivated Vero cell-derived SA 14-14-2 strain can increase immunity to Japanese encephalitis in adults who have completed primary vaccination with the inactivated mouse brain-derived Nakayama strain [25]. However, because there is no data on immunological reactions or adverse effects between other Japanese encephalitis vaccines, further studies are necessary.