Interim Estimates of 2023–2024Seasonal Influenza Vaccine Effectiveness Among Adults in Korea

In the 2023–2024 season, the influenza epidemic in South Korea peaked earlier than in recent years. In this study, we aimed to estimate the interim vaccine effectiveness (VE) of the influenza vaccination to prevent influenza during the early season. From November 1, 2023, to December 31, 2023, we enrolled 2,632 subjects with influenza-like illness from eight hospitals participating in hospital-based influenza morbidity and mortality surveillance. A retrospective test-negative case-control study was conducted to estimate the VE. The results showed an adjusted VE of 22.5% (95% confidence interval [CI], 6.6 to 35.8) for the total population. The adjusted VE was 22.3% (95% CI, 6.1 to 35.7) for influenza A and 9.4% (95% CI, −51.3 to 45.7) for influenza A/H1N1. Full results of the analysis will be reported.

Establishment of Safety Monitoring System for Vaccines Not Included in the National Immunization Program in Korea

Background@#In Korea, there are no surveillance programs for vaccines that are not included in the national immunization program (NIP), and vaccine safety monitoring in the adult population is inadequate. This study aimed to establish a safety monitoring system for nonNIP vaccines in adults. @*Methods@#Frequently administered non-NIP vaccines were selected. Individuals were included if they received at least one of the selected vaccines at a participating institution and provided informed consent. Solicited and unsolicited adverse events were monitored using questionnaires sent through text messages on days 1, 3, 7, 28, and 90 post-vaccination.Selected adverse events of special interest (AESIs) were monitored monthly by retrospective review of electronic medical records. Causality was assessed according to the Korea Disease Control and Prevention Agency guidelines. @*Results@#Four vaccines (tetanus-diphtheria-pertussis [Tdap], pneumococcal conjugate 13-valent [PCV13], live zoster vaccine [ZVL], and recombinant zoster vaccine [RZV]) were selected, and their safety profiles were monitored at four tertiary hospitals and 10 primary care clinics. The response rates of the questionnaires on post-vaccination days 1, 7, 28, and 90 were 99.2%, 93.6%, 81.0%, and 48.7%, respectively. Of 555 AESI identified over 10 months, 10 cases received one of the selected non-NIP vaccines within 90 days of the event. @*Conclusion@#We are establishing the first safety monitoring system for selected non-NIP vaccines in Korea since September 2022 and report its progress as of July 2023. However, continuous government support is essential for its maintenance and improvement.

Effectiveness of Bivalent mRNA Booster Vaccine Against COVID-19 in Korea

Background@#Bivalent booster mRNA vaccines containing the omicron-variant strains have been introduced worldwide in the autumn of 2022. Nevertheless, the omicron subvariants evoked another large coronavirus disease 2019 (COVID-19) pandemic wave in late 2022 and early 2023. @*Methods@#A retrospective, test-negative, case-control study was conducted to estimate the vaccine effectiveness (VE) of bivalent COVID-19 vaccines in 8 university hospitals between January and February 2023. The case and control groups were divided based on nasopharyngeal COVID-19 real-time polymerase chain reaction results and matched based on age, sex, hospital, and date (week) of the test performed. The VE of the BA.1- or BA.4/BA.5-based mRNA vaccines were estimated. VE was calculated using the 1−adjusted odds ratio from multivariable logistic regression. @*Results@#In total, 949 patients and 947 controls were enrolled in this study. VE for the BA.4/ BA.5-based bivalent mRNA vaccine was 43% (95% confidence interval [CI], 17, 61%). In subgroup analysis based on age and underlying medical conditions, BA.4/BA.5-based bivalent mRNA vaccine was effective against old adults aged ≥ 65-years (VE, 55%; 95% CI, 23, 73%) and individuals with comorbidities (VE, 54%; 95% CI, 23, 73%). In comparison, the BA.1-based bivalent mRNA vaccine did not demonstrate statistically significant effectiveness (VE, 25%; 95% CI, −8, 49%). @*Conclusion@#The BA.4/BA.5-based bivalent mRNA booster vaccine provided significant protection against COVID-19 in the Korean adults, especially in the older adults aged ≥ 65 years and in individuals with underlying medical conditions.

Impact of Infection Prevention Programs on Catheter-Associated Urinary Tract Infections Analyzed in Multicenter Study

Background@#Catheter-associated urinary tract infections (CAUTIs) account for a large proportion of healthcare-associated infections and have a significant impact on morbidity, length of hospital stay, and mortality. Adherence to the recommended infection prevention practices can effectively reduce the incidence of CAUTIs. This study aimed to assess the characteristics of CAUTIs and the efficacy of prevention programs across hospitals of various sizes. @*Methods@#Intervention programs, including training, surveillance, and monitoring, were implemented. Data on the microorganisms responsible for CAUTIs, urinary catheter utilization ratio, rate of CAUTIs per 1,000 device days, and factors associated with the use of indwelling catheters were collected from 2017 to 2019. The incidence of CAUTIs and associated data were compared between university hospitals and small- and medium-sized hospitals. @*Results@#Thirty-two hospitals participated in the study, including 21 university hospitals and 11 small- and medium-sized hospitals. The microorganisms responsible for CAUTIs and their resistance rates did not differ between the two groups. In the first quarter of 2018, the incidence rate was 2.05 infections/1,000 device-days in university hospitals and 1.44 infections/1,000 device-days in small- and medium-sized hospitals. After implementing interventions, the rate gradually decreased in the first quarter of 2019, with 1.18 infections/1,000 device-days in university hospitals and 0.79 infections/1,000 device-days in small- and medium-sized hospitals. However, by the end of the study, the infection rate increased to 1.74 infections/1,000 device-days in university hospitals and 1.80 infections/1,000 device-days in small- and medium-sized hospitals. @*Conclusion@#We implemented interventions to prevent CAUTIs and evaluated their outcomes. The incidence of these infections decreased in the initial phases of the intervention when adequate support and personnel were present. The rate of these infections may be reduced by implementing active interventions such as consistent monitoring and adherence to guidelines for preventing infections.

Human resources and medical supplies consumption during the COVID-19 pandemic: a single-center study / 고신대학교의과대학학술지

Background@#In the face of the unexpected coronavirus disease 2019 (COVID-19) pandemic, every country has struggled with insufficient human resources and medical supplies. This study aims to provide the statistical information necessary for discussing how to model stockpiles of medical resources. @*Methods@#This study was conducted at the Hallym University Kangnam Sacred Heart Hospital, in South Korea. The study duration was 2 weeks, centered on March 16, 2022, when the number of daily confirmed patients with COVID-19 in Korea peaked. The number of human resources was obtained by counting the number of healthcare workers using CCTV. Drug prescriptions and medical device usage were obtained from electronic medical records. @*Results@#In total, 117 inpatients and 26,485 outpatients were managed at this hospital during the 2-week study period. Daily visits were highest among nurses in all units, followed by doctors and radiology technicians. The mean daily consumption of personal protective equipment (PPE) per bed was 4.3 sets in the intensive care unit (ICU), 1.8 in the semi-ICU, and 1.4 in the ward. Despite the four-fold difference in the number of patients, there was no statistically significant difference between the two wards in the number of daily visits. Drug prescription rates were higher among inpatients than at-home patients. @*Conclusions@#The higher the COVID-19 severity, the higher the consumption of PPE per patient. Among healthcare workers, nurses had the highest number of inpatient treatment visits for COVID-19. To efficiently utilize, PPE, structures containing more isolation beds in a single negative pressure isolation system would be preferred.

Effectiveness and Adverse Events of Nirmatrelvir/Ritonavir Versus Molnupiravir for COVID-19 in Outpatient Setting: Multicenter Prospective Observational Study

Background@#In this study, we aimed to compare the effectiveness and adverse reactions of nirmatrelvir/ritonavir and molnupiravir in high-risk outpatients with coronavirus disease 2019 (COVID-19). @*Methods@#This multicenter prospective observational study evaluated the rate of hospitalization, death, and adverse events within 28 days of oral antiviral agent prescription (molnupiravir, n = 240; nirmatrelvir/ritonavir, n = 240) to 480 nonhospitalized adult patients with COVID-19 from August 2, 2022 to March 31, 2023. @*Results@#Patients receiving molnupiravir had a higher prevalence of comorbidities (85.8% vs. 70.4%; P < 0.001) and a higher Charlson comorbidity index (2.8 ± 1.4 vs. 2.5 ± 1.5; P = 0.009) than those receiving nirmatrelvir/ritonavir. Three patients required hospitalization (nirmatrelvir/ritonavir group, n = 1 [0.4%]; molnupiravir group, n = 2 [0.8%]; P = 1.000). Nirmatrelvir/ritonavir was associated with a higher risk of adverse events than molnupiravir (odds ratio [OR], 1.96; 95% confidence interval [CI], 1.27–3.03), especially for patients aged 65 years and older (OR, 3.04; 95% CI, 1.71–5.39). The severity of adverse events in both groups was mild to moderate and improved after discontinuation of medication. In the molnupiravir group, age ≥ 65 years (OR, 0.43 95% CI, 0.22–0.86) and appropriate vaccination (OR, 0.37; 95% CI, 0.15–0.91) reduced the occurrence of adverse events. @*Conclusion@#The rates of hospitalization and death were low and not significantly different between high-risk patients who received either nirmatrelvir/ritonavir or molnupiravir. Although adverse events were more frequent with nirmatrelvir/ritonavir than with molnupiravir, none were severe. Nirmatrelvir/ritonavir can be safely used to treat COVID-19, while molnupiravir could be considered as an alternative treatment option for high-risk groups.

Community-Acquired Pneumococcal Pneumonia in Highly Vaccinated Population: Analysis by Serotypes, Vaccination Status, and Underlying Medical Conditions

Background@#Targeted risk population has been highly vaccinated against pneumococcal diseases in South Korea. Despite this, the pneumococcal serotype distribution is evolving, which impedes efficient roll-out of vaccines. @*Methods@#This prospective cohort study included patients aged ≥ 19 years with communityacquired pneumonia (CAP) from five university hospitals in South Korea between September 2018 and July 2021. The outcomes of interest were the demographic and clinical characteristics of patients with CAP, pneumococcal serotype distribution, and risk factors of 30-day mortality in patients with pneumococcal CAP (pCAP). Considering the high seroprevalence, we analyzed the clinical characteristics of serotype 3 pCAP. @*Results@#A total of 5,009 patients hospitalized with CAP was included (mean age ± standard deviation, 70.3 ± 16.0 years; 3,159 [63.1%] men). Streptococcus pneumoniae was the leading causative agent of CAP (11.8% overall, 17.7% in individuals aged < 65 years with chronic medical conditions). Among the 280 serotyped Streptococcus pneumococcus, serotype 3 was the most common (10.0%), followed by serotypes 19A (8.9%), 34 (8.9%), and 35B (8.9%).Non-vaccine serotypes (serotype 35B [13.9%] and 34 [12.0%]) were the most prevalent in 108 individuals vaccinated with 23-valent pneumococcal polysaccharide vaccine (PPSV23).Serotype 3 was prevalent, irrespective of PPSV23 vaccination status, and more common in individuals with chronic lung disease (P = 0.008). Advanced age (adjusted odds ratio [aOR], 1.040; 95% confidence interval [CI], 1.011–1.071), long-term care facility residence (aOR, 2.161; 95% CI, 1.071–4.357), and bacteremia (aOR, 4.193; 95% CI, 1.604–10.962) were independent risk factors for 30-day mortality in patients with pCAP. PPSV23 vaccination reduced the risk of mortality (aOR, 0.507; 95% CI, 0.267–0.961). @*Conclusion@#Serotype 3 and 19A were still the most common serotypes of pCAP in South Korea despite the national immunization program of 13-valent pneumococcal conjugated vaccine in children and PPSV23 in old adults. PPSV23 vaccination might reduce the risk of mortality in patients with pCAP.

Multi-faceted analysis of COVID-19 epidemic in the Republic of Korea considering Omicron variant: Mathematical modeling-based study

BackgroundThe most recent variant of concern, Omicron (B.1.1.529), has caused numerous cases worldwide including the Republic of Korea due to its fast transmission and reduced vaccine effectiveness. MethodsA mathematical model considering age-structure, vaccine, antiviral treatment, and influx of the Omicron variant was developed. We estimated transmission rates among age groups using maximum likelihood estimation for the age-structured model. The impact of nonpharmaceutical interventions (in community and border), quantified by a parameter in the force of infection, and vaccination were examined through a multi-faceted analysis. A theory-based endemic equilibrium study was performed to find the manageable number of cases according to Omicron-and healthcare-related factors. ResultsBy fitting the model to the available data, the estimated values of ranged from 0.31 to 0.73, representing the intensity of nonpharmaceutical interventions such as social distancing level. If < 0.55 and 300,000 booster shots were administered daily from February 3, 2022, the number of severe cases was forecasted to exceed the severe bed capacity. Moreover, the number of daily cases is reduced as the timing of screening measures is delayed. If screening measure was intensified as early as November 24, 2021 and the number of overseas entrant cases was contained to 1 case per 10 days, simulations showed that the daily incidence by February 3, 2022 could have been reduced by 87%. Furthermore, we found that the incidence number in mid-December 2021 exceeded the theory-driven manageable number of daily cases. ConclusionNonpharmaceutical interventions, vaccination, and antiviral therapy influence the spread of Omicron and number of severe cases in the Republic of Korea. Intensive and early screening measures during the emergence of a new variant is key in controlling the epidemic size. Using the endemic equilibrium of the model, a formula for the manageable daily cases depending on the severity rate and average length of hospital stay was derived so that the number of severe cases does not surpass the severe bed capacity.

Safety and immunogenicity of a SARS-CoV-2 recombinant protein nanoparticle vaccine (GBP510) adjuvanted with AS03: a phase 1/2, randomized, placebo-controlled, observer-blinded trial

BackgroundVaccination has helped to mitigate the COVID-19 pandemic. Ten traditional and novel vaccines have been listed by the World Health Organization for emergency use. Additional alternative approaches may better address ongoing vaccination globally, where there remains an inequity in vaccine distribution. GBP510 is a recombinant protein vaccine, which consists of self-assembling, two-component nanoparticles displaying the receptor-binding domain (RBD) in a highly immunogenic array. MethodsWe conducted a randomized, placebo-controlled, observer-blinded, phase 1/2 trial to evaluate the safety and immunogenicity of GBP510 (2-doses at a 28-day interval) adjuvanted with or without AS03 in adults aged 19-85 years. The main outcomes included solicited and unsolicited adverse events; anti-SARS-CoV-2 RBD IgG antibody and neutralizing antibody responses; T-cell immune responses. FindingsOf 328 participants who underwent randomization, 327 participants received at least 1 dose of vaccine. Each received either 10 g GBP510 adjuvanted with AS03 (n = 101), 10 g unadjuvanted GBP510 (n = 10), 25 g GBP510 adjuvanted with AS03 (n = 104), 25 g unadjuvanted GBP510 (n = 51), or placebo (n = 61). Most solicited adverse events were mild-to-moderate in severity and transient. Higher reactogenicity was observed in the GBP510 adjuvanted with AS03 groups compared to the non-adjuvanted and placebo groups. Reactogenicity was higher post-dose 2 compared to post-dose 1, particularly for systemic adverse events. The geometric mean concentrations of anti-SARS-CoV-2-RBD IgG antibody reached 2163.6/2599.2 BAU/mL in GBP510 adjuvanted with AS03 recipients (10 g/25 g) by 14 days after the second dose. Two-dose vaccination with 10 g or 25 g GBP510 adjuvanted with AS03 induced high titers of neutralizing antibody via pseudovirus (1369.0/1431.5 IU/mL) and wild-type virus (949.8/861.0 IU/mL) assays. InterpretationGBP510 adjuvanted with AS03 was well tolerated and highly immunogenic. These results support further development of the vaccine candidate, which is currently being evaluated in Phase 3. FundingCoalition for Epidemic Preparedness Innovations RESEARCH IN CONTEXTO_ST_ABSEvidence before this studyC_ST_ABSWe searched PubMed for research articles published by December 31, 2021, using the terms "COVID-19" or "SARS-CoV-2," "vaccine," and "clinical trial." In previously reported randomized clinical trials, we found that mRNA vaccines were more immunogenic than adenovirus-vectored vaccines. Solicited adverse events were more frequent and more severe in intensity after the first dose compared to the second dose for adenovirus-vectored vaccines, whereas they increased after the second dose of mRNA or recombinant spike-protein nanoparticle vaccines. Added value of this studyThis is the first human study evaluating the immunogenicity and safety of recombinant SARS-CoV-2 protein nanoparticle with and without adjuvant AS03, designed to elicit functional cross-protective responses via receptor-binding domain (RBD). Both 10 and 25 g of GBP510 with AS03 formulations were well tolerated with an acceptable safety profile. Potent humoral immune responses against the SARS-CoV-2 RBD were induced and peaked by day 42 (14 days after the second dose). In addition, GBP510 adjuvanted with AS03 elicited a noticeable Th1 response, with production of IFN-{gamma}, TNF-, and IL-2. IL-4 was inconsistent and IL-5 nearly inexistent response across all groups. Implications of the available evidenceThe results from this phase 1/2 trial indicate that GBP510 adjuvanted with AS03 has an acceptable safety profile with no vaccine-related serious adverse events. Two-dose immunization with GBP510 adjuvanted with AS03 induced potent humoral and cellular immune responses against SARS-CoV-2.

Correlation Between Third Dose of COVID-19 Vaccines and Regional Case Fatality Rates During the Omicron Wave in Korea

This study seeks to find the correlation between case fatality rates (CFRs) and third-dose vaccination coverage in 244 counties (si/gun/gu) of South Korea during the omicron variant wave. Multivariate regression analyses report that the higher third-dose vaccination rates were correlated with lower regional CFRs, when controlling for age structure. If the thirddose vaccination rate of a county is higher by 10%, it would have a CFR lower by 0.05% (95% confidence interval, 0.03–0.08%). As the number of cumulative confirmed cases in South Korea was 16,353,495 as of April 20, 2022, a lower CFR by 0.03–0.08% is equivalent to 4,394–12,448 lives (8.6–24.4 per 100,000) spared. County-specific characteristics, such as age structure, intensive care unit availability, and the level of non-pharmaceutical interventions may also affect the extent of this correlation. The conclusion implicates the potential role of coronavirus disease 2019 vaccines in reducing the pressure on the regional healthcare capacity.

Nirmatrelvir/Ritonavir Prescription Rate and Outcomes in Coronavirus Disease 2019: A Single Center Study / 감염과화학요법

Background@#Nirmatrelvir/ritonavir was Korea's first oral antiviral agent to treat coronavirus disease 2019 (COVID-19). We analyzed the nirmatrelvir/ritonavir prescription rate and treatment outcomes in treatment-eligible patients with COVID-19 receiving home-based care. @*Materials and Methods@#We retrospectively collected data of patients with COVID-19-eligible for nirmatrelvir/ritonavir treatment from January 14, 2022, to February 15, 2022. We analyzed the prescription rate of nirmatrelvir/ritonavir, the reasons for non-prescription, and patient outcomes. @*Results@#A total of 414 patients were included, of whom 44.2% were male, and the mean age was 64.6 (standard deviation [SD] = 8.5). Approximately 73.2% (n = 303) of patients were not prescribed nirmatrelvir/ritonavir. More than fourth-fifths of the patients refused nirmatrelvir/ ritonavir treatment (n = 262, 86.5%). The mean symptom duration was significantly shorter in the prescription group (5.2 days [SD = 2.3] vs. 4.4 days [SD = 1.9], P = 0.001). A total of 6 (1.4%) patients were hospitalized, and none of the patients who received nirmatrelvir/ ritonavir required admission. Among the patients prescribed nirmatrelvir/ritonavir (n = 111), 17 (15.3%) patients experienced side effects, and 5 (4.5%) patients discontinued nirmatrelvir/ ritonavir due to side effects. @*Conclusion@#The nirmatrelvir/ritonavir prescription rate was low, with more than fourth-fifths of non-prescriptions being due to patient refusal. Symptom resolution was faster, and no life-threatening side effects were reported. Accurate information about drug safety must be provided to patients to make informed decisions regarding nirmatrelvir/ritonavir treatment.

Multi-Faceted Analysis of COVID-19Epidemic in Korea Considering Omicron Variant: Mathematical Modeling-Based Study

Background@#The most recent variant of concern, omicron (B.1.1.529), has caused numerous cases worldwide including the Republic of Korea due to its fast transmission and reduced vaccine effectiveness. @*Methods@#A mathematical model considering age-structure, vaccine, antiviral drugs, and influx of the omicron variant was developed. We estimated transmission rates among age groups using maximum likelihood estimation for the age-structured model. The impact of non-pharmaceutical interventions (NPIs; in community and border), quantified by a parameter μ in the force of infection, and vaccination were examined through a multi-faceted analysis. A theory-based endemic equilibrium study was performed to find the manageable number of cases according to omicron- and healthcare-related factors. @*Results@#By fitting the model to the available data, the estimated values of μ ranged from 0.31 to 0.73, representing the intensity of NPIs such as social distancing level. If μ < 0.55 and 300,000 booster shots were administered daily from February 3, 2022, the number of severe cases was forecasted to exceed the severe bed capacity. Moreover, the number of daily cases is reduced as the timing of screening measures is delayed. If screening measure was intensified as early as November 24, 2021 and the number of overseas entrant cases was contained to 1 case per 10 days, simulations showed that the daily incidence by February 3, 2022 could have been reduced by 87%. Furthermore, we found that the incidence number in mid-December 2021 exceeded the theory-driven manageable number of daily cases. @*Conclusion@#NPIs, vaccination, and antiviral drugs influence the spread of omicron and number of severe cases in the Republic of Korea. Intensive and early screening measures during the emergence of a new variant is key in controlling the epidemic size. Using the endemic equilibrium of the model, a formula for the manageable daily cases depending on the severity rate and average length of hospital stay was derived so that the number of severe cases does not surpass the severe bed capacity.

Oral antiviral clevudine compared with placebo in Korean COVID-19 patients with moderate severity

BackgroundClevudine, an antiviral drug for chronic hepatitis B virus infection, is expected to inhibit the replication of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus. Therefore, we conducted a prospective, single-blind, proof of concept clinical study to examine the antiviral efficacy and safety of clevudine compared to placebo in Korean corona virus disease 19 (COVID-19) patients with moderate severity. MethodsAdults with confirmed SARS-CoV-2 infection and symptom onset within 7 days were randomized 2:1 to 120 mg clevudine or placebo to receive one of treatments orally once-daily for 14 days. Antiviral efficacy outcomes were the proportion of patients with real-time reverse transcription polymerase chain reaction (RT-PCR) negative result for SARS-CoV-2 infection and cycle threshold (Ct) value changes from baseline. Clinical efficacy outcomes included proportion of patients who showed improvement in lung involvement by imaging tests, proportion of patients with normal body temperature, proportion of patients with normal oxygen saturation, and the changes in C-reactive protein (CRP) from baseline. Safety outcomes included changes in clinical laboratory tests, vital signs measurement, and physical examination from baseline, and incidence of adverse events. ResultsThe proportion of patients with real-time RT-PCR negative test and Ct value changes showed no significant difference between clevudine group and placebo group. The changes in Ct value from baseline were significantly greater in clevudine group compared to placebo group in patients with hypertension, and patients who underwent randomization during the first 5 and 7 days after the onset of symptoms. All clinical efficacy outcomes had no significant difference between clevudine group and placebo group. Clevudine was well tolerated and there was no significant difference in safety profile between two treatment groups. ConclusionsThis is the first clinical study to compare the antiviral efficacy and safety of clevudine to placebo in Korean COVID-19 patients with moderate severity. The study has demonstrated a possible favorable outcome for the reduction of SARS-CoV-2 replication, with acceptable safety profile, when COVID-19 patients were treated with clevudine. Further large-scale clinical studies, preferably with various clinical endpoints and virus titer evaluation, are required to better understand the effectiveness of using clevudine in COVID-19 treatment. Considering recent trend in clinical development for antiviral drugs, we need to design a clinical study aiming for reducing clinical risk of COVID-19 in mild to moderate patients with at least one risk factor for serious illness.

Quantifying the effects of non-pharmaceutical and pharmaceutical interventions against COVID-19 epidemic in the Republic of Korea: Mathematical model-based approach considering age groups and the Delta variant

BackgroundEarly vaccination efforts and non-pharmaceutical interventions were insufficient to prevent a surge of coronavirus disease 2019 (COVID-19) cases triggered by the Delta variant. This study aims to understand how vaccination and variants contribute to the spread of COVID-19 so that appropriate measures are implemented. MethodsA compartment model that includes age, vaccination, and infection with the Delta or non-Delta variants was developed. We estimated the transmission rates using maximum likelihood estimation and phase-dependent reduction effect of non-pharmaceutical interventions (NPIs) according to government policies from 26 February to 8 October 2021. We extended our model simulation until 31 December considering the initiation of eased NPIs. Furthermore, we also performed simulations to examine the effect of NPIs, arrival timing of Delta variant, and speed of vaccine administration. ResultsThe estimated transmission rate matrices show distinct pattern, with the transmission rates of younger age groups (0 39 years) much larger than non-Delta. Social distancing (SD) level 2 and SD4 in Korea were associated with transmission reduction factors of 0.64 to 0.69 and 0.70 to 0.78, respectively. The easing of NPIs to a level comparable to SD2 should be initiated not earlier than 16 October to keep the number of severe cases below the capacity of Koreas healthcare system. Simulation results also showed that a surge prompted by the spread of the Delta variant can be prevented if the number of people vaccinated daily was larger. ConclusionsSimulations showed that the timing of easing and intensity of NPIs, vaccination speed, and screening measures are key factors in preventing another epidemic wave. 2 Key MessagesO_LIMaximum likelihood estimation can be utilized to determine the transmission rates of the Delta and non-Delta variants. C_LIO_LIThe phase-dependent NPIs implemented by the Korean government were effectively quantified in the modelling study. C_LIO_LIEven with fast vaccination, resurgence of cases is still possible if NPIs are eased too early or screening measures are relaxed. C_LIO_LIThe model can be used as a guide for policy makers on deciding appropriate SD level that considers not only disease control, but also the socio-economic impact of maintaining strict measures. C_LI

Fit Test for N95 Filtering Facepiece Respirators and KF94 Masks for Healthcare Workers: a Prospective Single-center Simulation Study

Background@#For protection against coronavirus disease 2019 (COVID-19), the Korean government recommended the KF94 mask or that a mask at the same level as the KF94 should be worn when contacting a patient with COVID-19. Furthermore, adequately fitted N95 respirators and KF94 masks are essential. We investigated the fit tests to determine whether healthcare workers had adequate protection with N95 respirators and KF94 masks. @*Methods@#In this prospective single-center simulation study, five N95 respirators (two made in the USA by 3M and three made in Korea) and six KF94 masks, the Korean standard medical masks, were tested. The fit factor (FF) and leakage rate were evaluated using a two-fit test device. Adequate protection (defined as FF ≥ 100 or leakage rate ≤ 5) rates were compared between N95 respirators and KF94 masks, and between made in Korea and the 3M N95 respirators. For KF94 masks, adequate protection rates were compared before and after ear strap fixation. @*Results@#Overall, 30 participants were enrolled, and 330 fit tests were performed for FF and leakage rate. Adequate protection rates of all tested N95 respirators and KF94 masks were 22.7% (n = 75) by FF and 20.6% (n = 68) by leakage rate. N95 respirators showed a significantly higher adequate protection rate than KF94 masks for FF (48.7% vs. 1.1%, P < 0.001) and leakage rate (42.0% vs. 2.8%, P < 0.001). Adequate protection rate of 3M-made N95 respirators was significantly higher than that of those made in Korea (83.3% vs. 25.6% in FF, P < 0.001; 73.3% vs. 21.1% in leakage rate, P < 0.001). In KF94 masks, after fixation of ear strap with a hook, adequate protection rate improved significantly (1.1% vs. 12.8% in FF, P< 0.001; 2.8% vs. 11.1%, P < 0.001). @*Conclusion@#Although adequate protection rate of N95 respirators was higher than that of KF94 masks, N95 respirator protection rate was not optimum. Thus, it is necessary to minimize exposure to risk by selecting an appropriate mask or respirator that adequately fits each person, and by wearing respirators or masks appropriately, before contacting the patients. With their superior protection rate, wearing N95 respirators is recommended instead of KF94 masks, especially when performing aerosol-generating procedures.

Fit Test for N95 Filtering Facepiece Respirators and KF94 Masks for Healthcare Workers: a Prospective Single-center Simulation Study

Background@#For protection against coronavirus disease 2019 (COVID-19), the Korean government recommended the KF94 mask or that a mask at the same level as the KF94 should be worn when contacting a patient with COVID-19. Furthermore, adequately fitted N95 respirators and KF94 masks are essential. We investigated the fit tests to determine whether healthcare workers had adequate protection with N95 respirators and KF94 masks. @*Methods@#In this prospective single-center simulation study, five N95 respirators (two made in the USA by 3M and three made in Korea) and six KF94 masks, the Korean standard medical masks, were tested. The fit factor (FF) and leakage rate were evaluated using a two-fit test device. Adequate protection (defined as FF ≥ 100 or leakage rate ≤ 5) rates were compared between N95 respirators and KF94 masks, and between made in Korea and the 3M N95 respirators. For KF94 masks, adequate protection rates were compared before and after ear strap fixation. @*Results@#Overall, 30 participants were enrolled, and 330 fit tests were performed for FF and leakage rate. Adequate protection rates of all tested N95 respirators and KF94 masks were 22.7% (n = 75) by FF and 20.6% (n = 68) by leakage rate. N95 respirators showed a significantly higher adequate protection rate than KF94 masks for FF (48.7% vs. 1.1%, P < 0.001) and leakage rate (42.0% vs. 2.8%, P < 0.001). Adequate protection rate of 3M-made N95 respirators was significantly higher than that of those made in Korea (83.3% vs. 25.6% in FF, P < 0.001; 73.3% vs. 21.1% in leakage rate, P < 0.001). In KF94 masks, after fixation of ear strap with a hook, adequate protection rate improved significantly (1.1% vs. 12.8% in FF, P< 0.001; 2.8% vs. 11.1%, P < 0.001). @*Conclusion@#Although adequate protection rate of N95 respirators was higher than that of KF94 masks, N95 respirator protection rate was not optimum. Thus, it is necessary to minimize exposure to risk by selecting an appropriate mask or respirator that adequately fits each person, and by wearing respirators or masks appropriately, before contacting the patients. With their superior protection rate, wearing N95 respirators is recommended instead of KF94 masks, especially when performing aerosol-generating procedures.

Antibiotic Resistance Patterns of Enterobacteriaceae Isolated from Patients with Healthcare-Associated Infections / 감염과화학요법

Background@#There have been recent proposals to categorize healthcare-associated infections (HCAIs) separately from community-acquired infections (CAIs). The aim of this study was to compare the antibiotic resistance of pathogens causing CAIs, HCAIs, and hospital-acquired infections (HAIs) in Korea, and to investigate the need for different empirical antibiotics therapy for CAIs and HCAIs. @*Materials and Methods@#This prospective study was conducted in a university hospital between March and December 2019. Inpatients who underwent a bacterial culture within 2 days of hospitalization, with a Enterobacteriaceae strain identified at the infection site and available antibiotic susceptibility results, were included in the analysis. Infections were classified as CAIs, HCAIs or HAIs, depending on the source. @*Results@#Of the 146 patients included in the analysis, the prevalence of fluoroquinoloneresistant Enterobacteriaceae was 18.8%, 38.5%, and 55.0%; the prevalence of pathogens showing third-generation cephalosporins resistance was 8.3%, 50.0%, and 60.0%; and the prevalence of pathogens showing piperacillin-tazobactam resistance was 8.3%, 7.7%, 15.0% in the CAIs, HCAIs, and HAIs groups, respectively. The prevalence of extended-spectrum beta-lactamase-positive pathogens was 6.3%, 47.3%, and 55.0% in the CAIs, HCAIs, and HAIs group, respectively, with no significant difference between the HCAIs and HAIs groups. Resistance patterns of the HCAIs group more closely resembled those of the HAIs group than those of the CAIs group. @*Conclusion@#The pathogens isolated from patients with HCAIs showed resistance patterns that were more similar to those of patients with HAIs than those with CAIs. Thus, CAIs and HCAIs should be distinguished from each other when selecting antibiotic agents.

Antibiotic Resistance Patterns of Enterobacteriaceae Isolated from Patients with Healthcare-Associated Infections / 감염과화학요법

Background@#There have been recent proposals to categorize healthcare-associated infections (HCAIs) separately from community-acquired infections (CAIs). The aim of this study was to compare the antibiotic resistance of pathogens causing CAIs, HCAIs, and hospital-acquired infections (HAIs) in Korea, and to investigate the need for different empirical antibiotics therapy for CAIs and HCAIs. @*Materials and Methods@#This prospective study was conducted in a university hospital between March and December 2019. Inpatients who underwent a bacterial culture within 2 days of hospitalization, with a Enterobacteriaceae strain identified at the infection site and available antibiotic susceptibility results, were included in the analysis. Infections were classified as CAIs, HCAIs or HAIs, depending on the source. @*Results@#Of the 146 patients included in the analysis, the prevalence of fluoroquinoloneresistant Enterobacteriaceae was 18.8%, 38.5%, and 55.0%; the prevalence of pathogens showing third-generation cephalosporins resistance was 8.3%, 50.0%, and 60.0%; and the prevalence of pathogens showing piperacillin-tazobactam resistance was 8.3%, 7.7%, 15.0% in the CAIs, HCAIs, and HAIs groups, respectively. The prevalence of extended-spectrum beta-lactamase-positive pathogens was 6.3%, 47.3%, and 55.0% in the CAIs, HCAIs, and HAIs group, respectively, with no significant difference between the HCAIs and HAIs groups. Resistance patterns of the HCAIs group more closely resembled those of the HAIs group than those of the CAIs group. @*Conclusion@#The pathogens isolated from patients with HCAIs showed resistance patterns that were more similar to those of patients with HAIs than those with CAIs. Thus, CAIs and HCAIs should be distinguished from each other when selecting antibiotic agents.

Air Evacuation of Passengers with Potential SARS-CoV-2Infection Under the Guidelines for Appropriate Infection Control and Prevention

This report describes the air evacuation of 80 Koreans from Iran to Korea on March 19 th , 2020, with a direct transfer of passengers between airplanes in Dubai. The passengers were potentially infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) so, strict precautions were taken for the duration of the flight, and the passengers were screened before embarking from Dubai and disembarking at Incheon International Airport in Korea. Passengers with fever or symptoms of SARSCoV-2 were assessed by a quarantine doctor, and if they were suspected of being infected with SARSCoV-2, they were categorized as a “patient under investigation (PUI)”. There was 1 passenger designated as a PUI before the departure from Dubai and another designated as a PUI upon arrival into Korea. The first PUI tested negative, but the second PUI tested positive for SARS-CoV-2. All those aboard the flight (passengers, aircrew, and medical staff) were screened for SARS-CoV-2 upon arrival into Korea and completed a mandatory 14-day medical quarantine. There were no additional cases of infection.

Seroprevalence of Anti-SARS-CoV-2 Antibodies among Outpatients in Southwestern Seoul, Korea

Serosurveillance studies reveal the actual disease burden and herd immunity level in the population. In Seoul, Korea, a cross-sectional investigation showed 0.07% anti-severe acute respiratory syndrome coronavirus-2 antibody seropositivity among 1,500 outpatients of the university hospitals. Low seroprevalence reflects well-implemented social distancing.Serosurveillance should be repeated as the pandemic progresses.