The Korean Society of Infectious Diseases has regularly updated its adult immunization guidelines, including the coronavirus disease 2019 (COVID-19) vaccination recommendations in 2023 and the 2024–2025 seasonal update. This article provides a comprehensive update as of September 2025, reflecting the latest evidence and international guidance. Focusing on the 2025–2026 season, it reviews vaccines currently authorized in Korea and their effectiveness against predominant JN.1 sublineage variants, including LP.8.1, NB.1.8.1, and XFG. The updated recommendations prioritize vaccination with LP.8.1-adapted vaccines for high-risk groups—adults aged 65 years and older, individuals aged 6 months and older at increased risk for severe disease, and residents of facilities vulnerable to infection—while vaccination remains available for all individuals aged 6 months and older. A single-dose strategy is generally recommended, although older adults and immunocompromised individuals may consider an additional dose at 6-month intervals in consultation with healthcare professionals. These updates aim to refine Korea’s COVID-19 vaccination strategy and sustain protection in high-risk populations, with recommendations remaining subject to revision as new evidence and epidemiological conditions evolve.

The 20-valent pneumococcal conjugate vaccine (PCV20) was approved by the Korean Ministry of Food and Drug Safety in October 2024. Despite the ongoing national immunization programs that include pneumococcal conjugate vaccines for children and 23-valent pneumococcal polysaccharide vaccine (PPSV23) for adults, the burden of invasive pneumococcal disease and pneumococcal community-acquired pneumonia remains high among the elderly and high-risk adults. Serotypes 3 and 19A, both included in 13-valent pneumococcal conjugate vaccine (PCV13), continue to be the most prevalent serotypes, and infections caused by non-PCV13 serotypes have increased. Given the need to broaden serotype coverage and simplify vaccination strategies, the Korean Society of Infectious Diseases recommends either a single dose of PCV20 or sequential vaccination with 15-valent pneumococcal conjugate vaccine followed by PPSV23 for adults aged 65 years and older, and for high-risk adults aged 19–64 years. These recommendations are based on immunogenicity, safety, and cost-effectiveness data from recent clinical trials. Vaccine selection, dosing intervals, and schedules should be determined according to individual underlying medical conditions and previous vaccination history to optimize protection against pneumococcal disease in the adult population.

Annual influenza vaccination is strongly recommended for immunocompromised individuals, who are at a higher risk of severe infection. The Korean Society of Infectious Diseases has revised its influenza vaccination recommendations for solid organ transplant recipients, advocating for the use of highly immunogenic vaccines, such as high-dose inactivated influenza vaccines or MF59-adjuvanted inactivated influenza vaccines, to enhance vaccine efficacy. While further research is needed to extend these recommendations to other immunocompromised populations, these vaccines have demonstrated improved immunogenicity without compromising safety. Expanding vaccination guidelines to additional immunocompromised groups should be considered as more evidence emerges.

Background: This study presents a framework for determining the allocation and distribution of the limited amount of vaccines against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Methods: After analyzing the pandemic strategies of the major organizations and countries and with a literature review conducted by a core panel, a modified Delphi survey was administered to 13 experts in the fields of vaccination, infectious disease, and public health in the Republic of Korea. The following topics were discussed: 1) identifying the objectives of the vaccination strategy, 2) identifying allocation criteria, and 3) establishing a step-by-step vaccination framework and prioritization strategy based on the allocation criteria. Two rounds of surveys were conducted for each topic, with a structured questionnaire provided via e-mail in the first round. After analyzing the responses, a meeting with the experts was held to obtain consensus on how to prioritize the population groups. Results: The first objective of the vaccination strategy was maintenance of the integrity of the healthcare system and critical infrastructure, followed by reduction of morbidity and mortality and reduction of community transmission. In the initial phase, older adult residents in care homes, high-risk health and social care workers, and personal support workers who work in direct contact with coronavirus disease 2019 (COVID-19) patients would be prioritized. Expansion of vaccine supply would allow immunization of older adults not included in phase 1, followed by healthcare workers not previously included and individuals with comorbidities. Further widespread vaccine supply would ensure availability to the extended adult age groups (50–64 years old), critical workers outside the health sector, residents who cannot socially distance, and, eventually, the remaining populations. Conclusion: This survey provides the much needed insight into the decision-making process for vaccine allocation at the national level. However, flexibility in adapting to strategies will be essential, as new information is constantly emerging.

Background/Aims: Unlike Western countries, the 2009 pandemic influenza infection among pregnant women was reported as mild in a previous interim study in South Korea. However, several mortalities were reported thereafter, suggesting that nationwide data were lacking. Methods: This case-control study covers the entire 2009 pandemic inf luenza period, from May 2009 to February 2010. The clinical and economic data of pregnant (case) and age-matched non-pregnant (control) women with influenza A (H1N1) pdm09 virus (H1N1pdm09) infection were retrospectively collected from nine hospitals in South Korea. Results: A total of 130 pregnant women with H1N1pdm09 infection were identified. The mean age of the pregnant women was 31.1 years (range, 19 to 41) and mean gestational age was 18.4 weeks (range, 3 to 40). Both case and control groups were similar in terms of age (p = 0.43) and comorbidities (p = 0.18). The overall rate of complications was comparable between the two groups (p = 0.648). However, mortality was reported only among the cases, so mean economic per capita burden is estimated to be higher for pregnant women compared to the control (4,821,992 Korean won [KRW] vs. 351,233 KRW, p = 0.31). Obstetric complications were observed in 12 cases, including preterm labor (n = 7), low birth-weight (n = 3), miscarriage (n = 1), stillbirth (n = 1), and cleft lip (n = 1). Conclusions: Although statistically insignificant, the detrimental impact of influenza A H1N1pdm09 on pregnancy can be serious in some complicated cases in South Korea. Thus, the strong recommendation of influenza vaccination should be maintained for pregnant women as a high priority.

Campylobacter infection causes gastrointestinal symptoms such as abdominal pain or diarrhea. Occasionally, Campylobacter bacteremia affects immunocompromised patients; however, serious outcomes are known to be rare. Here, we present a case of a patient with Campylobacter bacteremia who had underlying liver cirrhosis. The patient had fever and diarrhea. These symptoms subsided after treatment with cefotaxime. Campylobacter jejuni was isolated in the blood culture after 10 days. In addition, previously reported cases of Campylobacter bacteremia in Asian countries were reviewed with respect to antimicrobial sensitivities.

Background: The World Health Organization recommends the surveillance of influenza-like illness (ILI) and severe acute respiratory infection (SARI) to respond effectively to both seasonal influenza epidemics and pandemics. In Korea, the “Hospital-based Influenza Morbidity and Mortality (HIMM)” surveillance system has been operated to monitor ILI and SARI occurrences. Materials and Methods: A multi-center prospective observational study was conducted. Adult patients with acute respiratory infection (ARI) were enrolled during the 2011-12, 2012-2013, and 2013-2014 influenza seasons at the 10 university hospitals using the HIMM surveillance system. With respect to SARI and pneumonia development, risk profiles were analyzed in patients with ARI in Korea. Results: A total of 5,459 cases were eligible for this analysis. Among 5,459 cases with ARI, 2,887 cases (52.9%) were identified that they had influenza infection. Among enrolled cases, 750 cases belonged to the SARI group, while 4,709 cases belonged to the non-SARI group. With respect to pneumonia development, 317 cases were accompanied by pneumonia, and 5,142 cases were not. Multivariate analyses revealed that the following factors were associated with an increased risk of SARI: Old age (≥65 Hospiyears) (odds ratio [OR] 2.69, 95% confidence interval [CI] 2.2-3.32), chronic heart disease (CHD) (OR 2.24, 95% CI 1.68-2.98), cerebrovascular disease (CVD) (OR 1.49, 95% CI 1.05-2.10), chronic obstructive pulmonary disease (COPD) (OR 2.34, 95% CI 1.48-3.69), asthma (OR 2.33, 95% CI 1.62-3.36), chronic kidney disease (CKD) (OR 2.62, 95% CI 1.73-3.99), chronic liver disease (OR 1.71, 95% CI 1.04-2.81), and autoimmune diseases (OR 2.53, 1.57-4.08). Multivariate analyses revealed that the following factors were independent risk factors for pneumonia development: Old age (≥65 years) (OR 5.71, 95% CI 4.10-7.94), CHD (OR 1.54, 95% CI 1.07-2.22), COPD (OR 2.34, 95% CI 1.48-3.69), asthma (OR 2.33, 95% CI 1.62-3.36), CKD (OR 2.62, 95% CI 1.73-3.99), immunocompromised conditions (OR 3.12, 95% CI 1.47-6.62), and autoimmune diseases (OR 3.35, 95% CI 1.79-6.27). The risk of SARI and pneumonia was increased by the number of concurrent chronic medical conditions. Conclusion: The risk of SARI and pneumonia development among adult patient with ARI was significantly increased by the presence or number of concurrent chronic medical conditions in Korea.

Pregnant women are prioritized to receive influenza vaccination. However, the maternal influenza vaccination rate has been low in Korea. To identify potential barriers for the vaccination of pregnant women against influenza, a survey using a questionnaire on the perceptions and attitudes about maternal influenza vaccination was applied to Korean obstetricians between May and August of 2014. A total of 473 respondents participated in the survey. Most respondents (94.8%, 442/466) recognized that influenza vaccination was required for pregnant women. In addition, 92.8% (410/442) respondents knew that the incidence of adverse events following influenza vaccination is not different between pregnant and non-pregnant women. However, 26.5% (124/468) obstetricians strongly recommended influenza vaccination to pregnant women. The concern about adverse events following influenza vaccination was considered as a major barrier for the promotion of maternal influenza vaccination by healthcare providers. Providing professional information and education about maternal influenza vaccination will enhance the perception of obstetricians about influenza vaccination to pregnant women and will be helpful to improve maternal influenza vaccination coverage in Korea.