Performance of the Galactomannan Test for the Diagnosis of Invasive Pulmonary Aspergillosis using Non-invasive Proximal Airway Samples.

OBJECTIVE: To diagnose invasive pulmonary aspergillosis (IPA), galactomannan (GM) detection in serum or bronchoalveolar lavage fluid (BALF) is widely used. However, the utility of proximal airway GM test (from induced sputum or tracheal aspirate) has not been well elucidated. METHODS: In this retrospective cohort study, we evaluated the diagnostic performance of proximal airway GM in diagnosis of IPA including COVID-19 associated pulmonary aspergillosis (CAPA). Between January 2022 and January 2023, patients who had been tested for GM with clinical suspicion or for surveillance from any specimen (serum, induced sputum, tracheal aspirate, and BALF) were screened. IPA was diagnosed using EORTC/MSGERC criteria, and CAPA was diagnosed following the 2020 ECMM/ISHAM consensus criteria. RESULTS: Of 624 patients with GM results, 70 met the criteria for proven/probable IPA and 427 had no IPA. The others included possible IPA and chronic form of aspergillosis. The sensitivities and specificities of serum, proximal airway, and BALF GM for proven/probable IPA versus no IPA were 78.9% and 70.6%, 93.1% and 78.7%, and 78.6% and 91.0%, respectively. Areas under the receiver operating characteristic curve (AUCs) were 0.742 for serum GM, 0.935 for proximal airway GM, and 0.849 for BALF GM (serum GM vs proximal airway GM, p = 0.014; proximal airway GM vs BALF GM, p = 0.334; serum GM vs BALF GM, p = 0.286). CONCLUSION: This study demonstrates that the performance of GM test from non-invasive proximal airway samples is comparable or even better than those from serum and distal airway sample (BALF).

Infection-related Hospitalizations During Immune Checkpoint Inhibitor Treatment Without Immunosuppressants.

Immunosuppressants are increasingly being used in the clinic to manage immune-related adverse effects. Consequently, the incidence of secondary infections associated with immunosuppression is increasing. However, little is known about primary infections during immune checkpoint inhibitor (ICI) treatment without immunosuppressants. We aimed to evaluate primary infectious diseases during antiprogrammed death ligand-1 immunotherapy without immunosuppressants. We retrospectively screened medical records of 233 patients who underwent ICI treatment for advanced non-small cell lung cancer between January 2014 and May 2018 at National Cancer Center, Republic of Korea. Subsequently, we evaluated the clinical characteristics and treatment outcomes of selected patients hospitalized for potential infectious disease without immunosuppressive treatment (n=80). Eight cases (3.4%) were identified as bacterial pneumonia (n=5) and cellulitis, inflamed epidermoid cyst, and wound infection (n=1 each). The bacterial pathogens Streptococcus pneumoniae and Haemophilus influenzae were identified in 4 patients with pneumonia. The period between the start of ICI treatment and infection varied between 3 and 189 days (median, 24.5 days). Five (62.5%) patients were infected within a month after ICI treatment initiation. All patients were treated with empirical antibiotics and discharged without complications. The median progression-free and overall survival for ICI treatment was 11.5 and 25.5 months, respectively. Six patients experienced ICI-associated adverse effects postinfection: Herpes zoster infection (n=4) and pneumonitis (n=2). Infectious disease independent of immunosuppression is a rare, but possible event in patients with lung cancer receiving ICI treatment. Clinical awareness would enable prompt diagnosis of primary infection during immunotherapy.

Delirium in patients with COVID-19 treated in the intensive care unit.

Coronavirus disease 2019 (COVID-19) can lead to acute organ dysfunction, and delirium is associated with long-term cognitive impairment and a prolonged hospital stay. This retrospective single-center study aimed to investigate the risk factors for delirium in patients with COVID-19 infection receiving treatment in an intensive care unit (ICU). A total of 111 patients aged >18 years with COVID-19 pneumonia who required oxygen therapy from February 2021 to April 2022 were included. Data on patient demographics, past medical history, disease severity, delirium, and treatment strategies during hospitalization were obtained from electronic health records. Patient characteristics and risk factors for delirium were analyzed. Old age (P < 0.001), hypertension (P < 0.001), disease severity (Sequential Organ Failure Assessment score) (P < 0.001), mechanical ventilator support (P < 0.001), neuromuscular blocker use (P < 0.001), and length of stay in the ICU (P < 0.001) showed statistically significant differences on the univariable analysis. Multivariable analysis with backward selection revealed that old age (odds ratio, 1.149; 95% confidence interval, 1.037-1.273; P = 0.008), hypertension (odds ratio, 8.651; 95% confidence interval, 1.322-56.163; P = 0.024), mechanical ventilator support (odds ratio, 226.215; 95% confidence interval, 15.780-3243.330; P < 0.001), and length of stay in the ICU (odds ratio, 30.295; 95% confidence interval, 2.539-361.406; P = 0.007) were significant risk factors for delirium. In conclusion, old age, ICU stay, hypertension, mechanical ventilator support, and neuromuscular blocker use were predictive factors for delirium in COVID-19 patients in the ICU. The study findings suggest the need for predicting the occurrence of delirium in advance and preventing and treating delirium.

Predicting factors associated with prolonged intensive care unit stay of patients with COVID-19.

BACKGROUND: Predicting the length of stay (LOS) for coronavirus disease 2019 (COVID-19) patients in the intensive care unit (ICU) is essential for efficient use of ICU resources. We analyzed the clinical characteristics of patients with severe COVID-19 based on their clinical care and determined the predictive factors associated with prolonged LOS. METHODS: We included 96 COVID-19 patients who received oxygen therapy at a high-flow nasal cannula level or above after ICU admission during March 2021 to February 2022. The demographic characteristics at the time of ICU admission and results of severity analysis (Sequential Organ Failure Assessment [SOFA], Acute Physiology and Chronic Health Evaluation [APACHE] II), blood tests, and ICU treatments were analyzed using a logistic regression model. Additionally, blood tests (C-reactive protein, D-dimer, and the PaO2 to FiO2 ratio [P/F ratio]) were performed on days 3 and 5 of ICU admission to identify factors associated with prolonged LOS. RESULTS: Univariable analyses showed statistically significant results for SOFA score at the time of ICU admission, C-reactive protein level, high-dose steroids, mechanical ventilation (MV) care, continuous renal replacement therapy, extracorporeal membrane oxygenation, and prone position. Multivariable analysis showed that MV care and P/F ratio on hospital day 5 were independent factors for prolonged ICU LOS. For D-dimer, no significant variation was observed at admission; however, after days 3 and 5 days of admission, significant between-group variation was detected. CONCLUSIONS: MV care and P/F ratio on hospital day 5 are independent factors that can predict prolonged LOS for COVID-19 patients.

Identifying susceptibility of children and adolescents to the Omicron variant (B.1.1.529).

BACKGROUND: The Omicron variant (B.1.1.529) is estimated to be more transmissible than previous strains of SARS-CoV-2 especially among children, potentially resulting in croup which is a characteristic disease in children. Current coronavirus disease 2019 (COVID-19) cases among children might be higher because (i) school-aged children have higher contact rates and (ii) the COVID-19 vaccination strategy prioritizes the elderly in most countries. However, there have been no reports confirming the age-varying susceptibility to the Omicron variant to date. METHODS: We developed an age-structured compartmental model, combining age-specific contact matrix in South Korea and observed distribution of periods between each stage of infection in the national epidemiological investigation. A Bayesian inference method was used to estimate the age-specific force of infection and, accordingly, age-specific susceptibility, given epidemic data during the third (pre-Delta), fourth (Delta driven), and fifth (Omicron driven) waves in South Korea. As vaccine uptake increased, individuals who were vaccinated were excluded from the susceptible population in accordance with vaccine effectiveness against the Delta and Omicron variants, respectively. RESULTS: A significant difference between the age-specific susceptibility to the Omicron and that to the pre-Omicron variants was found in the younger age group. The rise in susceptibility to the Omicron/pre-Delta variant was highest in the 10-15 years age group (5.28 times [95% CI, 4.94-5.60]), and the rise in susceptibility to the Omicron/Delta variant was highest in the 15-19 years age group (3.21 times [95% CI, 3.12-3.31]), whereas in those aged 50 years or more, the susceptibility to the Omicron/pre-Omicron remained stable at approximately twofold. CONCLUSIONS: Even after adjusting for contact pattern, vaccination status, and waning of vaccine effectiveness, the Omicron variant of SARS-CoV-2 tends to propagate more easily among children than the pre-Omicron strains.

Epidemiology and Transmission Dynamics of Infectious Diseases and Control Measures.

The epidemiology and transmission dynamics of infectious diseases must be understood at the individual and community levels to improve public health decision-making for real-time and integrated community-based control strategies. Herein, we explore the epidemiological characteristics for assessing the impact of public health interventions in the community setting and their applications. Computational statistical methods could advance research on infectious disease epidemiology and accumulate scientific evidence of the potential impacts of pharmaceutical/nonpharmaceutical measures to mitigate or control infectious diseases in the community. Novel public health threats from emerging zoonotic infectious diseases are urgent issues. Given these direct and indirect mitigating impacts at various levels to different infectious diseases and their burdens, we must consider an integrated assessment approach, 'One Health', to understand the dynamics and control of infectious diseases.

Age-Varying Susceptibility to the Delta Variant (B.1.617.2) of SARS-CoV-2.

Importance: The Delta variant (B.1.617.2) is estimated to be more transmissible than previous strains of SARS-CoV-2, especially among children and adolescents. However, to our knowledge, there are no reports confirming this to date. Objective: To gain a better understanding of the association of age with susceptibility to the Delta variant of SARS-CoV-2. Design, Setting, and Participants: This decision analytic model used an age-structured compartmental model using the terms symptom onset (S), exposure (E), infectious (I), and quarantine (Q) (SEIQ) to estimate the age-specific force of infection, combining age-specific contact matrices and observed distribution of periods between each stage of infection (E to I [ie, latent period], I given S, and S to Q [ie, diagnostic delay]) developed in a previous contact tracing study. A bayesian inference method was used to estimate the age-specific force of infection (S to E) and, accordingly, age-specific susceptibility. The age-specific susceptibility during the third wave (ie, before Delta, from October 15 to December 22, 2020, when the COVID-19 vaccination campaign was not yet launched) and the fourth wave (ie, the Delta-driven wave, from June 27 to August 21, 2021) in Korea were compared. As vaccine uptake increased, individuals who were vaccinated were excluded from the susceptible population in accordance with vaccine effectiveness against the Delta variant. This nationwide epidemiologic study included individuals who were diagnosed with COVID-19 during the study period in Korea. Data were analyzed from September to November 2021. Exposures: Age group during the third wave (ie, before Delta) and fourth wave (ie, Delta-driven) of the COVID-19 pandemic in South Korea. Main Outcomes and Measures: Age-specific susceptibility during the third and fourth waves was estimated. Results: Among 106 866 confirmed COVID-19 infections (including 26 597 infections and 80 269 infections during the third and fourth waves of COVID-19 in Korea, respectively), a significant difference in age-specific susceptibility to the Delta vs pre-Delta variant was found in the younger age group. After adjustment for contact pattern and vaccination status, the increase in susceptibility to the Delta vs pre-Delta variant was estimated to be highest in the group aged 10 to 15 years, approximately doubling (1.92-fold increase [95% CI, 1.86-fold to 1.98-fold]), whereas in the group aged 50 years or more, susceptibility to the Delta vs pre-Delta variant remained stable at an approximately 1-fold change (eg, among individuals aged 50-55 years: 0.997-fold [95% CI, 0.989-fold to 1.001-fold). Conclusions and Relevance: In this study, the Delta variant of SARS-CoV-2 was estimated to propagate more easily among children and adolescents than pre-Delta strains, even after adjusting for contact pattern and vaccination status.

Contact-adjusted Immunity Levels against SARS-CoV-2 in Korea and Prospects for Achieving Herd Immunity.

The proportion of population vaccinated cannot be directly translated into the herd immunity. We have to account for the age-stratified contact patterns to calculate the population immunity level, since not every individual gathers evenly. Here, we calculated the contact-adjusted population immunity against severe acute respiratory syndrome coronavirus 2 in South Korea using age-specific incidence and vaccine uptake rate. We further explored options to achieve the theoretical herd immunity with age-varying immunity scenarios. As of June 21, 2021, when a quarter of the population received at least one dose of a coronavirus disease 2019 (COVID-19) vaccine, the contact-adjusted immunity level was 12.5% under the social distancing level 1. When 80% of individuals aged 10 years and over gained immunity, we could achieve a 58.2% contact-adjusted immunity level. The pros and cons of vaccinating children should be weighed since the risks of COVID-19 for the young are less than the elderly, and the long-term safety of vaccines is still obscure.

Cancer Patients' Willingness to Take COVID-19 Vaccination: A Nationwide Multicenter Survey in Korea.

Considering the high morbidity and mortality of Coronavirus disease 2019 (COVID-19) in patients with malignancy, they are regarded as a priority for COVID-19 vaccination. However, general vaccine uptake rates among cancer patients are known to be lower than in their healthy counterparts. Thus, we aimed to investigate the attitude and acceptance rates for the COVID-19 vaccine in cancer patients and identify predictive factors for vaccination that could be modified to increase vaccine uptake rates, via a paper-based survey (58 items over six domains). A total of 1001 cancer patients participated in this nationwide, multicenter survey between February and April 2021. We observed that 61.8% of respondents were willing to receive the COVID-19 vaccine. Positive predictive factors found to be independently associated with vaccination were male gender, older age, obesity, previous influenza vaccination history, absence of cancer recurrence, time since cancer diagnosis over 5 years, and higher EuroQol Visual Analogue Scale scores. Along with the well-known factors that are positively correlated with vaccination, here, we report that patients' disease status and current health status were also associated with their acceptance of the COVID-19 vaccination. Moreover, 91.2% of cancer patients were willing to be vaccinated if their attending physicians recommend it, indicating that almost 30% could change their decision upon physicians' recommendation. Unlike other factors, which are unmodifiable, physicians' recommendation is the single modifiable factor that could change patients' behavior. In conclusion, we firstly report that Korean cancer patients' acceptance rate of the COVID-19 vaccination was 61.8% and associated with disease status and current health status. Physicians should play a major role in aiding cancer patients' decision-making concerning COVID-19 vaccines.

Presepsin in the Rapid Response System for Cancer Patients: A Retrospective Analysis.

INTRODUCTION: Early diagnosis of sepsis is paramount to effective management. The present study aimed to compare the prognostic accuracy of presepsin levels and other biomarkers in the assessment of septic shock and mortality risk in cancer patients. MATERIALS AND METHODS: A total of 74 cancer patients were evaluated for presepsin, lactic acid, C-reactive protein (CRP) levels, and white blood cell count (WBC). Specificity and sensitivity values for septic shock and death were compared between four biomarkers in all patients and those with and without acute kidney injury (AKI). RESULTS: A total of 27 and 29 patients experienced septic shock and died, respectively. The area under the curve (AUC) and sensitivity and specificity estimated for presepsin levels for septic shock were 60%, 74%, and 51%, respectively. The corresponding values for mortality were 62%, 72%, and 49%, respectively. In patients without AKI, AUC of presepsin levels for septic shock and death were 62% and 65%, respectively; in those with AKI, these values were 44% and 58%, respectively. Presepsin levels showed higher sensitivity and specificity values than WBC and higher specificity than CRP but were similar to those of lactic acid levels. CONCLUSIONS: Presepsin levels are similar to lactic acid levels in the assessment of septic shock and mortality risk in cancer patients. In patients with AKI, presepsin levels should be considered carefully.

The Impact of COVID-19 on Cancer Care in the Post Pandemic World: Five Major Lessons Learnt from Challenges and Countermeasures of Major Asian Cancer Centres.

OBJECTIVE: The COVID-19 pandemic has dramatically affected healthcare services around Asia. The Asian National Cancer Centres Alliance and the Asia-Pacific Organisation for Cancer Prevention collaborated to assess the mid- and long- term impact of COVID-19 to cancer care in Asia. METHODS: The two entities organised a combined symposium and post-meeting interactions among representatives of major cancer centres from seventeen Asian countries to outlining major challenges and countermeasures. RESULTS: Participating stakeholders distilled five big questions. 1) "Will there be an explosion of late-stage cancers after the pandemic?" To address and recover from perceived delayed prevention, screening, treatment and care challenges, collaboration of key stakeholders in the region and alignment in cancer care management, policy intervention and cancer registry initiatives would be of essential value. 2) "Operations and Finance" The pandemic has resulted in significant material and financial casualties. Flagged acute challenges (shortages of supplies, imposition of lockdown) as well as longer-standing reduction of financial revenue, manpower, international collaboration, and training should also be addressed. 3) "Will telemedicine and technological innovations revolutionize cancer care?" Deploying and implementing telemedicine such as teleconsultation and virtual tumour boards were considered invaluable. These innovations could become a new regular practice, leading to expansion of tele-collaboration through collaboration of institutions in the region. 4) "Will virtual conferences continue after the pandemic?" Virtual conferences during the pandemic have opened new doors for knowledge sharing, especially for representatives of low- and middle-income countries in the region, while saving time and costs of travel. 5) "How do we prepare for the next pandemic or international emergency?" Roadmaps for action to improve access to appropriate patient care and research were identified and scrutinised. CONCLUSION: Through addressing these five big questions, focused collaboration among members and with international organisations such as City Cancer Challenge will allow enhanced preparedness for future international emergencies.
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Guidelines for Cancer Care during the COVID-19 Pandemic in South Korea.

At the end of 2019, the cause of pneumonia outbreaks in Wuhan, China, was identified as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. In February 2020, the World Health Organization named the disease cause by SARS-CoV-2 as coronavirus disease 2019 (COVID-19). In response to the pandemic, the Korean Cancer Association formed the COVID-19 task force to develop practice guidelines. This special article introduces the clinical practice guidelines for cancer patients which will help oncologists best manage cancer patients during the COVID-19 pandemic.

Impact of a computerised clinical decision support system on vancomycin loading and the risk of nephrotoxicity.

BACKGROUND: A vancomycin loading dose is recommended for the treatment of serious methicillin-resistant Staphylococcus aureus (MRSA) infections. However, clinicians often do not adhere to these recommendations, mainly due to nephrotoxicity risk, unfamiliarity with the guideline, or complexity of calculating an individual dose. Therefore, we introduced a computerised clinical decision support system (CDSS) for vancomycin loading (hereafter Vancomycin CDSS) to promote the use of vancomycin loading dose. METHODS: We describe a quasi-experimental study spanning 6 months before and 18 months after the deployment of a Vancomycin CDSS. The Vancomycin CDSS was integrated into the hospital's electronic medical record system in the form of a vancomycin order set. Our primary endpoint was the incidence of nephrotoxicity; the secondary endpoint was mean initial vancomycin trough levels. We also conducted a survey to evaluate the reasons why clinicians opted not to utilise a vancomycin loading dose. RESULTS: After implementation of Vancomycin CDSS, 363 out of 746 patients (49 %) who were first administered vancomycin received a loading dose. We did not find significant differences in nephrotoxicity between the pre- and post-intervention groups, nor between the loading- and non-loading groups. In the pre-intervention group, the mean initial vancomycin trough level was 7.10 mg/L, which was significantly lower than that in the post-intervention group of 11.11 mg/L. In the vancomycin loading group, the mean initial trough level was 11.95 mg/L, compared to 7.55 mg/L in the non-loading group. The main reason stated for not prescribing a vancomycin loading dose was concern about nephrotoxicity. CONCLUSION: Introduction of the Vancomycin CDSS did not increase nephrotoxicity and increased the mean initial dose and trough level of vancomycin.

Immunogenicity and safety of a live herpes zoster vaccine in hematopoietic stem cell transplant recipients.

BACKGROUND: Herpes zoster (HZ) infection of hematopoietic stem cell transplant (HSCT) patients is of clinical concern. Vaccination could help restore immunity to varicella zoster virus (VZV); however, temporal changes in immunogenicity and safety of live HZ vaccines after HSCT is still unclear. The aim of this study was to elucidate the temporal immunogenicity and safety of the HZ vaccine according to time since HSCT and to determine optimal timing of vaccination. METHODS: Live HZ vaccine was administered to patients 2-5 years or > 5 years post-HSCT. Control groups comprised patients with a hematologic malignancy who received cytotoxic chemotherapy and healthy volunteers. Humoral and cellular immunogenicity were measured using a glycoprotein enzyme-linked immunosorbent assay (gpELISA) and an interferon-γ (IFN-γ) enzyme-linked immunospot (ELISPOT) assay. Vaccine-related adverse events were also monitored. RESULTS: Fifty-six patients with hematologic malignancy (41 in the HSCT group and 15 in the chemotherapy group) along with 30 healthy volunteers were enrolled. The geometric mean fold rises (GMFRs) in humoral immune responses of the 2-5 year and > 5 year HSCT groups, and the healthy volunteer group, were comparable and significantly higher than that of the chemotherapy group (3.15, 95% CI [1.96-5.07] vs 5.05, 95% CI [2.50-10.20] vs 2.97, 95% CI [2.30-3.83] vs 1.42, 95% CI [1.08-1.86]). The GMFR of cellular immune responses was highest in the HSCT 2-5 year group and lowest in the chemotherapy group. No subject suffered clinically significant adverse events or reactivation of VZV within the follow-up period. CONCLUSION: Our findings demonstrate that a live HZ vaccine is immunogenic and safe when administered 2 years post-HSCT.

Transmission onset distribution of COVID-19.

OBJECTIVES: The distribution of the transmission onset of COVID-19 relative to the symptom onset is a key parameter for infection control. It is often not easy to study the transmission onset time, as it is difficult to know who infected whom exactly when. METHODS: We inferred transmission onset time from 72 infector-infectee pairs in South Korea, either with known or inferred contact dates, utilizing the incubation period. Combining this data with known information of the infector's symptom onset, we could generate the transmission onset distribution of COVID-19, using Bayesian methods. Serial interval distribution could be automatically estimated from our data. RESULTS: We estimated the median transmission onset to be 1.31 days (standard deviation, 2.64 days) after symptom onset with a peak at 0.72 days before symptom onset. The pre-symptomatic transmission proportion was 37% (95% credible interval [CI], 16-52%). The median incubation period was estimated to be 2.87 days (95% CI, 2.33-3.50 days), and the median serial interval to be 3.56 days (95% CI, 2.72-4.44 days). CONCLUSIONS: Considering that the transmission onset distribution peaked with the symptom onset and the pre-symptomatic transmission proportion is substantial, the usual preventive measures might be too late to prevent SARS-CoV-2 transmission.

Clinical Score System to Differentiate Severe Fever with Thrombocytopenia Syndrome Patients from Patients with Scrub Typhus or Hemorrhagic Fever with Renal Syndrome in Korea.

BACKGROUND: Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease with high mortality in East Asia. This study aimed to develop, for primary care providers, a prediction score using initial symptoms and basic laboratory blood tests to differentiate between SFTS and other endemic zoonoses in Korea. METHODS: Patients aged ≥ 18 years diagnosed with endemic zoonoses during a 3-year period (between January 2015 and December 2017) were retrospectively enrolled from 4 tertiary university hospitals. A prediction score was built based on multivariate logistic regression analyses. RESULTS: Of 84 patients, 35 with SFTS and 49 with other endemic zoonoses were enrolled. In multivariate logistic regression analysis, independent predictors of SFTS included neurologic symptoms (odds ratio [OR], 12.915; 95% confidence interval [CI], 2.173-76.747), diarrhea (OR, 10.306; 95% CI, 1.588-66.895), leukopenia (< 4,000/mm³) (OR, 19.400; 95% CI, 3.290-114.408), and normal C-reactive protein (< 0.5 mg/dL) (OR, 24.739; 95% CI, 1.812-337.742). We set up a prediction score by assigning one point to each of these four predictors. A score of ≥ 2 had 82.9% sensitivity (95% CI, 71.7%-87.5%) and 95.9% specificity (95% CI, 88.0%-99.2%). The area under the curve of the clinical prediction score was 0.950 (95% CI, 0.903-0.997). CONCLUSION: This study finding suggests a simple and useful scoring system to predict SFTS in patients with endemic zoonoses. We expect this strategic approach to facilitate early differentiation of SFTS from other endemic zoonoses, especially by primary care providers, and to improve the clinical outcomes.

Estimating contact-adjusted immunity levels against measles in South Korea and prospects for maintaining elimination status.

Measles has been reemerging in South Korea since December 2018 resulting in 185 cases by September 2019. We calculated contact-adjusted immunity levels against measles in South Korea using national seroprevalence data in 2014, vaccination uptake rates, and an age-specific contact matrix. We further explored options to achieve a contact-adjusted immunity level of 93% for herd immunity. The assessed contact-adjusted immunity level has increased from 86% in 2014 to 92% in 2018. Herd immunity could be achieved with immunizing 50% of susceptibles among birth cohorts 1999-2003 in 2018. Contact-adjusted immunity levels against measles have increased recently in South Korea, although they might not yet be high enough to guarantee herd immunity.