Adult Immunization Policy in Korea

Abstract

Although adult immunization is different from children’s, vaccine preventable diseases (VPDs) for adults are significant in that they are more severe and cause more deaths than VPDs for children. Additionally, the emergence of new vaccines and an increase in the elderly population are increasing demands for policy support for adult vaccination. Accordingly, in this paper, I will look at the characteristics of adult immunization, policies that have been implemented in Korea, and considerations.

Introduction

Immunization is the most effective and cost-beneficial means of preventing infectious diseases [1]. Immunization not only reduces the incidence of disease, but also reduces the severity of disease, reduces disease costs, and improves quality of life. Accordingly, many countries recognize the vaccine as a very important part of public health policy and are implementing a certain level of immunization through the national immunization program (NIP) [2]. Most NIPs are for children, and NIPs for adults are for only a few vaccines, such as influenza vaccines [3]. However, due to the increase in the adult population, changes in the epidemiology of infectious diseases, and the emergence of new vaccines, the demand and importance of a national immunization policy targeting adults are growing day by day. Accordingly, in this paper, I will look at the characteristics of adult immunization and the NIP for adults in Korea, and describe the gap between the recommendations of professional societies and the NIP, and the considerations for an adult immunization policy in Korea.

Characteristics of adult immunization

In the case of vaccinations for children, the main purpose is to prevent the occurrence and spread of diseases by improving the immunity level of the population, whereas the main purpose of the vaccinations for adults is to improve an individual's health by reducing the individual's risk of infection, complications or death [4]. Therefore, vaccines for adults are not limited to diseases that can spread between people, and the shingles vaccine is a representative example [5].

However, while the incidence of vaccine preventable diseases (VPDs) in children has decreased significantly in recent years, VPDs in adults still occur frequently and cause more deaths, resulting in a greater disease burden [6,7]. According to a report by the World Health Organization, 90% of pneumonia or influenza-related deaths in high-income countries occurred in adults aged 65 years or older [8]. In the case of coronavirus disease 2019 (COVID-19), the risk of severe disease or death increases with age, so adults, especially the elderly, are considered the highest priority for vaccination [9,10,11,12].

In the case of childhood immunization, comprehensive standards are applied based on age in most cases, so the immunization standards and programs are relatively simple. In comparison, the adult immunization is more complicated because vaccination standards are established based on various factors such as age, underlying disease, and residence in a long-term care facility [13]. Older adults have lower effectiveness of common vaccines than typical children or young adults due to immunosenescence [14]. In the case of zoster vaccine live, clinical trial results have reported that vaccine efficacy decreases significantly as age increases [15,16]. Even in the case of influenza vaccines, elderly people have lower vaccine efficacy than adolescents or young adults [17]. However, when the enhanced influenza vaccine is administered to the elderly, vaccine efficacy improves [18,19,20]. Therefore, adult immunization requires various vaccine selection and strategies depending on the characteristics of the target.

National immunization program for adults in Korea

Vaccination in Korea began in 1882 when a cowpox station was established and cowpox vaccination was conducted [21]. When the Infectious Disease Prevention Act was first enacted in 1954, vaccination against seven types of infectious diseases was designated as routine immunization and until 2004, national immunization project was divided into routine immunization program (RIP) and temporary immunization program (TIP). RIP of infants and young children was carried out as a maternal and child health project, and TIP was managed at the quarantine level. However, with the establishment of the Korea Disease Control and Prevention Agency in December 2003, the national immunization project began to be carried out in a unified manner. Accordingly, the RIP and TIP was changed to the national immunization program (NIP) starting in 2004. The NIP has developed to expand support mainly for children. In 2009, a children's vaccination support program was launched in which the government partially subsidizes the costs of children under the age of 12 receiving eight types of essential vaccinations at private medical institutions. In 2014, the program was expanded to include full government support for vaccination costs for 11 types of vaccines. As of 2023, the children's national vaccination support program has been further expanded to 18 types of vaccines [22]. However, the NIP for adults has been carried out only in the form of temporary vaccination for some risk groups, with vaccination supported at public health centers. Since the mid-2000s, influenza vaccination has been provided free of charge at public health centers for all seniors aged 65 years or older. And this has become the most representative NIP for adults [23]. In 2013, a pneumococcal vaccination support program began to support vaccination with the 23-valent pneumococcal polysaccharide vaccine (PPSV23) for seniors aged 65 years or older, and in 2019, support for influenza vaccination for pregnant women began (Table 1). As of 2023, people eligible for NIP can receive both influenza and pneumococcal vaccines for free, even if they are administered at a private medical institution. Although it is not the area of NIP, a vaccination program for seven types of vaccines (tetanus-diphtheria-pertussis, hepatitis A, meningococcus, influenza, measles-mumps-rubella, typhoid fever, and hemorrhagic fever with nephrotic syndrome) is being implemented for military personnel [24].

Table 1. National immunization program for adults in Korea.

Program	Vaccine provided	Target population	Immunization rate (as of 2022)
Influenza vaccination program for elderly	Quadrivalent inactivated influenza vaccine	Elderly aged 65 years or older	81.9%a
Pneumococcal vaccination program for elderly	23-valent pneumococcal polysaccharide vaccine	Elderly aged 65 years or older	54.5%b
Influenza vaccination program for pregnant women	Quadrivalent inactivated influenza vaccine	Pregnant women	50.4%c

^aOf the 9,310,653 people eligible for vaccination, a total of 7,629,522 people were vaccinated, including 7,512,691 people who were vaccinated with government support and 116,831 people who were vaccinated at their own expense. If only government support is included, the vaccination rate is 80.7%.

^bVaccination rate among people born in 1957. Calculated as of November 30, 2022.

^cOf the 265,263 people eligible for vaccination, a total of 133,735 people were vaccinated, including 133,735 people who were vaccinated with government support and 265 people who were vaccinated at their own expense. If only government support is included, the vaccination rate is 50.3%.

Gap between NIP by government and recommendations by professional society

The Korean Society of Infectious Diseases (KSID) first developed a textbook for adult immunization in 2007, and has regularly updated the recommendations in line with newly developed vaccines or the expansion of those eligible for vaccination. While the society's guidelines mainly determine vaccination recommendations based on effectiveness, safety, and domestic epidemiology, in the case of NIP, budget, cost-effectiveness, administrative implementation feasibility, priorities, etc. must be considered, so there is a gap between the vaccine recommended by the society and NIP. In case of children, it takes a considerable amount of time to go through several procedures for the vaccine recommended by the society to be included in the NIP. For adults, however, the gap between the society's recommendations and the NIP is much larger, and the difference is gradually increasing. Currently, KSID recommends receiving more than 10 vaccines depending on age or situation [25]. In comparison, the NIP for adults implemented by the government only includes support for influenza and pneumococcal vaccinations for the elderly and influenza vaccination for pregnant women.

The most important thing to note between the society's recommendations and NIP is that NIP is not being applied to patients with chronic diseases and underlying diseases. In the case of the influenza vaccine, vaccination is recommended not only for the elderly but also for all children and adults over 6 months of age, and among them, those with underlying diseases are included in the priority group, where the need for vaccination is more emphasized. In the case of pneumococcal vaccine, vaccination is also recommended for people under 65 years of age and with underlying diseases. Currently, NIP tends to be implemented only in areas where criteria are clearly defined, such as age, and screening and vaccination support for patients with other conditions such as underlying diseases has rarely been applied other than the COVID-19 vaccine.

There is also a difference between the society's recommendations and the NIP in the type of vaccine recommended. In the case of pneumococcal vaccine, the society recommends the use of both pneumococcal conjugate vaccine and PPSV23 in adults, whereas NIP targets only PPSV23. In the case of influenza vaccines, the United States recently recommends the use of enhanced vaccines such as high dose, adjuvanted, and recombinant vaccines for seniors aged 65 years or older, and the recently revised guidelines from the KSID also contain the same recommendation. However, this enhanced influenza vaccine is not yet included in the NIP. Considering that the development of new vaccines for adults continues, the gap between the recommendations of professional societies and the contents of the NIP project is likely to widen further.

Considerations for adult immunization policy in Korea

In order to include adult vaccination in the NIP, there must be a social consensus on what the goals of the NIP are. In the case of NIP, there is an opinion that it should target diseases that can be transmitted between people, considering the public health impact. In the case of vaccines targeting adults, there are aspects that contribute to the formation of herd immunity, but reducing the risk of each vaccinated individual and lowering the disease burden becomes a more important goal. Therefore, it is argued that adult vaccination does not meet the purpose of NIP. However, it is important to remember that the vaccines currently included in the NIP do not only target diseases that can be transmitted from person to person. Tetanus and Japanese encephalitis are not diseases that can be transmitted between people, so even if the vaccination rate is high, herd immunity that can block transmission cannot be expected. Therefore, limiting the target of NIP to diseases that can be transmitted between people with the sole goal of forming herd immunity also raises problems with the legitimacy of the current NIP. It is appropriate to broadly understand the goal of NIP as reducing the incidence of VPDs and lowering the disease burden, and it is necessary to address adult vaccination from this perspective. From this perspective, cost-effectiveness evaluation is very important. In particular, considering that the social and economic burden of disease outbreaks is considerable, the cost-effectiveness analysis of vaccines from a social perspective is helpful in understanding the actual value of adult vaccination. In fact, cost-effectiveness analysis of adult vaccinations showed that most vaccines were cost-effective [26].

It should also be taken into account that new vaccines for adults continue to emerge and social demand for them is gradually growing. Over 80% of vaccines in the pipeline are being developed for adults, according to a report by Vaccines Europe [27]. The shingles vaccine, pneumococcal vaccine, and RSV vaccine, which have recently been approved and used domestically and internationally, are all targeted at adults. Accordingly, social demand for the vaccine is increasing.

However, in the case of adult immunization, the vaccine price is relatively expensive. Additionally, considering Korea's population aging trend, the introduction of NIP for adult vaccination is likely to cause a significant financial burden. Therefore, in evaluating the introduction of NIP, it is important to evaluate the operational feasibility of financial impact, sustainability, etc.

Due to its nature, adult vaccination is susceptible to political influence. Therefore, it is also important to operate an independent system that determines whether to introduce NIP based on objective evaluation results based on as much evidence as possible.

It is also necessary to consider how to expand coverage of high-risk groups with underlying diseases in Korea's current NIP operating system. In the current rigid NIP system, it is not easy to immediately select and apply NIP recipients based on the evidence and patient condition evaluation results. In this respect, it is necessary to consider covering adult immunization within the health insurance system. However, consideration is needed regarding the objectives of the health insurance system and a plan to maintain health insurance financial soundness.

Conclusion

The demand for support for adult immunization will gradually increase due to the development of new vaccines, the increase in the elderly population, and changes in infectious disease epidemiology. The adult immunization policy currently applied in Korea is relatively narrow and needs to be expanded in various directions. While understanding the importance of adult vaccination, an adult immunization policy should be developed taking its characteristics into consideration.