PHWR Public Health Weekly Report

1. Background of the Revision of “Immunization Standard and Method”

Immunization is one of the most effective and cost-beneficial public health measures for the prevention of infectious diseases. Immunization promotes human health by preventing the occurrence of infectious diseases as well as downgrading their severity. The Korea Disease Control and Prevention Agency (KDCA) first published the “Epidemiology and Management of Vaccine-Preventable Diseases” in 2005 [1]. This publication comprehensively summarizes various aspects of immunization to elucidate the epidemiology of vaccine-preventable infectious diseases in the Republic of Korea and promote effective use of vaccines. These guidelines have been revised periodically to reflect changes in immunization strategies. Table 1 highlights the publication history. It has been 6 years since the publication of the fifth edition of “Epidemiology and Management of Vaccine-Preventable Diseases” in 2017 [2]. Since then, there has been a need to include changes in epidemiological information, development of novel vaccines, and modifications of the matters approved for existing vaccines. Based on this, we introduce the major revisions in the sixth edition of “Immunization Standard and Method,” revised in 2023, in this article [3].

Table 1 Publication history

Year (month)	Title
2005 (January)	Epidemiology and management of vaccine preventable disease (1st ed)
2005 (July)	Epidemiology and management of vaccine preventable disease (2nd ed)
2006 (July)	Epidemiology and management of vaccine preventable disease (3rd ed)
2011 (December)	Epidemiology and management of vaccine preventable disease (4th ed)
2013 (May)	Epidemiology and management of vaccine preventable disease (4th revised ed)
2017 (April)	Epidemiology and management of vaccine preventable disease (5th ed)
2023 (June)	Immunization Standard and Method (6th ed)

1. Major Revisions of “Immunization Standard and Method”

Since the publication of “Epidemiology and Management of Vaccine-Preventable Diseases” in 2005 by the KDCA, guidelines have been periodically revised to incorporate the latest information to provide a reference document for public health centers and medical institutions that are involved in immunization strategies.

The KDCA began working on the sixth edition in 2021, and the editorial team consisted of members of subcommittees by sector under the Korea Advisory Committee on Immunization Practices (KACIP) and experts in the field for each infectious disease. The editorial team reviewed research literature in the Republic of Korea and abroad, including disease epidemiology and the latest research on the efficacy and safety of each vaccine. In addition, the editorial team incorporated immunization recommendations in the Republic of Korea and abroad, modifications of the matters approved for each vaccine, and novel vaccines. The KDCA supervised the actualization of standards for the diagnosis and reporting of infectious diseases and the needed revisions.

In this edition, certain immunization standards were revised to include recent changes and related academic societies and expert advisory committees in each field were consulted for the same. Finally, after deliberation by the KACIP, immunization standards in the Republic of Korea were changed. Local governments and the medical community were notified to ensure that healthcare professionals conducting immunization comply with the immunization standards.

The major revisions are stated in the subsequent paragraphs.

First, chapters for coronavirus disease 2019 (COVID-19), herpes zoster, and special cases, such as patients with chronic diseases and immunocompromised patients, were newly added, in order to address new infectious diseases, newly developed vaccines, and immunization guidelines for special cases. In the “Immunization Standard and Method”, a new chapter on COVID-19, a novel infectious disease, was added to describe the overall management of the disease, including epidemiology, diagnostic criteria, treatment strategies, and prevention measures. The fifth edition addressed chickenpox and herpes zoster in the same chapter, whereas the revised guidelines have separated the two diseases into individual chapters as their clinical aspects and vaccines for immunization are different. In addition, the revision includes novel vaccines for herpes zoster that were developed after publication of the fifth edition. Furthermore, chapters on special cases, such as patients with chronic diseases and immunocompromised patients, were newly added to address the specific immunization standards, including the timing and the method of immunization for such cases.

Second, we included the latest epidemiological information for various infectious diseases. Epidemiological information provides scientific evidence that aids in the protection of populations from diseases. The circumstances in which diseases occur differ in each country, or even in different places within a country, can change over time. In particular, the circumstances of disease occurrence for vaccine-preventable diseases change depending on the effectiveness of the vaccine and the vaccination rate. Hence, “Immunization Standard and Method” have been revised to include the latest epidemiological information on such vaccine-preventable infectious diseases.

Third, to reflect the revised diagnosis and reporting standards for national notifiable infectious diseases, the contents of the guideline of “2023 Case Definitions for National Notifiable Infectious Diseases” were uniformly incorporated into the diagnosis and reporting standards for each infectious disease [4]. The existing “Epidemiology and Management of Vaccine-Preventable Disease” was published in 2017; however, the classification of national notifiable infectious diseases was reorganized in 2020, and the notification of diagnostic criteria for reporting infectious diseases (KDCA Notification No. 2023-3) was partially revised. The revised “Immunization Standard and Method” uniformly applied the “2023 Case Definitions for National Notifiable Infectious Diseases” guidelines to actualize the diagnosis and reporting standards for infectious diseases.

Fourth, immunization standards have been partially revised to include epidemiological information, the latest research on vaccine effectiveness and safety, and the matters approved for existing vaccines. The immunization standards for Japanese encephalitis (inactivated vaccine), human papilloma virus infection, and herpes zoster (for patients undergoing hematopoietic stem cell transplantation), which are supported by the national immunization program, have been revised, and local governments and consigned medical institutions were notified to ensure that national immunization is implemented to reflect these changes. The immunization standards were partially revised to reflect the latest research for other immunization approaches not supported by the national immunization program. Table 2 highlights the major changes in the immunization standards.

Table 2 Summary table of major changes of Immunization Standard

	Before	After
IJEVa)	• (Interval between dose 1 to dose 2) 7–30 days, minimum interval 7 days	• (Interval between dose 1 to dose 2)1 month, minimum interval 4 weeksb)
	• (Age for dose 2) 12–23 months	• (Age for dose 2) 13–23 months
	• (Interval between dose 2 to dose 3) 12 months	• (Interval between dose 2 to dose 3) 11 months
	• (Definition of dose 3) Dose of Primary series	• (Definition of dose 3) Booster dose
HPVc)	• (2-dose series) ①. Age for dose 1HPV2, HPV9: Age 9–14 yearsHPV4: Age 9–13 years. ②. Interval between dose 1 to dose 2HPV2, HPV4: 6 monthsHPV9: 6–12 months. ③. Minimum interval between dose 1 to dose 2HPV2, HPV9: 5 monthsHPV4: 6 months.	• (2-dose series) Unify the age and interval of initial vaccination regardless of vaccine type ①. Age for dose 1: Age 9–14 years. ②. Interval between dose 1 to dose 2: 6–12 months. ③. Minimum interval between dose 1 to dose 2: 5 months.
	• (3-dose series) Age for dose 1 of HPV4: Age 14–26 years	• (3-dose series) Age for dose 1 of HPV4: Age 15–26 years
VAR for HSCTd)	• (Change the number of vaccination) Primary vaccinations (<13 year): 1 dose	• (Change the number of vaccination) Primary vaccinations (<13 year): 2–dose ※. Minimum interval between dose 1 to dose (<13 years): 3 months.

IJEV=inactivated Japanese encephalitis vaccine; HPV=human papilomavirus; VAR=varicella; HSCT=hematopoietic stem cell transplantation. ^a)IJEV: The second dose is conducted 1 month after the first dose, and booster dose is recommended 11 months after the second dose. ^b)If accelerated vaccination is required, such as staying in a country where Japanese encephalitis is prevalent for more than 30 days, the dose 2 can be vaccinated at least 7 days apart after the dose 1. ^c)HPV vaccine: If the first dose is started at the age of 9–14 years, it can be completed with 2-dose series. ^d)VAR vaccine for HSCT: Those under the age of 13 can be completed with 2-dose series..

Fifth, detailed guidelines on special circumstances that occur frequently during immunization in the field were added. With the development of science and technology, there are many different types of vaccines. Hence, many special circumstances occur in the field; for example, the standard immunization schedule cannot be applied at times due to specific existing health conditions. Thus, a specific schedule was added to reflect commonly occurring immunization situations, such as delayed vaccination, mis-vaccination, and heterologous vaccination. In addition, frequently asked questions (FAQs) were prepared for many situations related to each infectious disease to ensure safe immunization in the medical field.

This revision focused on revising the “Immunization Standard and Method” to reflect novel vaccines that were developed, changes in the matters approved for existing vaccines, and recent research. In addition, to clearly indicate the purpose of publication of these revisions, the existing “Epidemiology and Management of Vaccine-Preventable Disease” was renamed as “Immunization Standard and Method”. To summarize, “Immunization Standard and Method” is a standard for immunization, and we expect that “Immunization Standard and Method” will be used by healthcare professionals who administer immunization and related public officials to implement effective and safe immunization in the field. The KDCA will continue to revise “Immunization Standard and Method” in the future to reflect the situations in which infectious diseases occur, development of novel vaccines, and latest research in the Republic of Korea and abroad to contribute to public health through the prevention of infectious diseases.

Ethics Statement: Not applicable.

Funding Source: None.

Acknowledgments: We would like to extend our profound gratitude to the team members (Jiyeon-Shin, Minje-Kim, Seonghee-Kwon) now in charge of managing immunization standards at KDCA. They worked on the final proofreading before the publication of “Immunization Standard and Method” and tried to ensure that they were distributed smoothly. Their dedication deserve the highest commendation.

Conflict of Interest: The authors have no conflicts of interest to declare.

Author Contributions: Conceptualization: IJK. Data curation: IJK. Methodology: IJK, HJJ, HLL. Supervision: HLL, GYK. Writing – original draft: IJK. Writing – review & editing: HJJ, HLL, GYK.