Effectiveness of the Bivalent mRNA COVID-19 Vaccine for Preventing Critical Infection From the SARS-CoV-2 Omicron Variant in the Republic of Korea.

BACKGROUND: This retrospective observational matched cohort study assessed the differences in critical infections caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) during the omicron-predominant period of the coronavirus disease 2019 (COVID-19) pandemic. We evaluated the vaccine effectiveness of bivalent mRNA vaccine compared to unvaccinated individuals. METHODS: We collected COVID-19 case data from the Korean COVID-19 vaccine effectiveness cohort. We calculated the probability of critical COVID-19 cases by comparing the vaccinated and unvaccinated groups. RESULTS: The risk of being critically infected due to SAR-CoV-2 infection was 5.96 times higher (95% confidence interval, 5.63-6.38) among older individuals who were unvaccinated compared to those who received the bivalent COVID-19 vaccine. CONCLUSION: Our findings indicate that the bivalent vaccine reduces the disease burden of the SARS-CoV-2 omicron variant, particularly among the older population. Further studies are warranted to determine the effectiveness of booster doses of vaccines for SARS-CoV-2 infection.

Relationship between obesity, body composition, and pulmonary function among Korean adults aged 40 years and older.

Pulmonary function is influenced by factors such as age, sex, height, and weight. This study investigated the relationship between obesity, body composition, and pulmonary function measures (forced expiratory volume in one second [FEV1], forced vital capacity [FVC], and the FEV1-to-FVC ratio) of Korean adults aged 40 years and older. Using the fifth Korea national health and nutrition examination survey in 2010 and 2011, multiple regression analyses were performed to identify factors associated with pulmonary function, stratified by sex. Independent variables were waist circumference (WC) and an additional measure of obesity/muscularity (weight in model 1, body mass index [BMI] in model 2, and fat-free mass index [FFMI] in model 3). Among 3918 adults, the mean FFMI was 17.7 and 15.0 kg/m2 for men and women, respectively. Weight and BMI were positively associated with only FEV1 (B = 0.003 and B = 0.006, respectively, p < 0.01) and the FEV1-to-FVC ratio (B = 0.001, p < 0.01) in women. FFMI was positively associated with FEV1 and FVC in both sexes (B = 0.019, p < 0.05 for FEV1 and B = 0.020, p < 0.01 for FVC in men; B = 0.025, p < 0.0001 for FEV1 and B = 0.022, p < 0.0001 for FVC in women). WC was inversely associated with FEV1 and FVC in men and FEV1 in women, respectively. Weight and BMI behaved as indicators of body size based on their positive associations with pulmonary function. In conclusion, FFMI can be an important and consistent predictor of pulmonary function in both men and women.

Evaluation of an influenza-like illness sentinel surveillance system in South Korea, 2017-2023.

BACKGROUND: Guided by the data from the surveillance system, public health efforts have contributed to reducing the burden of influenza in many countries. During the COVID-19 pandemic, many surveillance resources were directed at tracking the severe acute respiratory syndrome-Coronavirus 2. However, most countries have not reported surveillance evaluations during the COVID-19 pandemic. METHODS: Using the U.S. CDC surveillance evaluation method, we evaluated the influenza-like illness (ILI) sentinel surveillance performance in South Korea between January 2017 and September 2023. For the timeliness, we measured the mean time lag between the reports from the sentinel sites to the Korea Disease Control and Prevention Agency (KDCA) and surveillance result dissemination from KDCA. For the completeness, we measured the submission rate of complete reports per overall number of reports from each sentinel site to the KDCA. For the sensitivity, we calculated the correlation coefficient between the monthly number of ILI reports and the patients with ILI from the Korea national reimbursement data by either Pearson's or Spearman's test. For the representativeness, we compared the age-specific distribution of ILI between the surveillance data and the national reimbursement data using a chi-squared test. RESULTS: We found that the surveillance performance of timeliness (less than 2 weeks) and completeness (97 %-98 %) was stable during the study period. However, we found a reduced surveillance sensitivity (correlation coefficient: 0.73 in 2020, and 0.84 in 2021) compared to that of 2017-2019 (0.96-0.99), and it recovered in 2022-2023 (0.93-0.97). We found no statistical difference across the proportion of age groups between the surveillance and reimbursement data during the study period (all P-values > 0.05). CONCLUSIONS: Ongoing surveillance performance monitoring is necessary to maintain efficient policy decision-making for the control of the influenza epidemic. Additional research is needed to assess the overall influenza surveillance system including laboratory and hospital-based surveillance in the country.

The Hand, Foot, and Mouth Disease Sentinel Surveillance System in South Korea: Retrospective Evaluation Study.

Background: South Korea has implemented a hand, foot, and mouth disease (HFMD) surveillance system since 2009 to monitor incidence trends and identify disease burden. This nationwide surveillance involves a network of approximately 100 pediatric clinics that report all probable and confirmed HFMD cases. Following the COVID-19 pandemic, infectious disease surveillance systems must be evaluated to ensure the effective use of limited public health resources. Objective: This study aimed to evaluate the HFMD sentinel surveillance system in South Korea from 2017 to 2022, focusing on the transition period after the COVID-19 pandemic. Methods: We retrospectively reviewed the HFMD sentinel surveillance system from the Korea Disease Control and Prevention Agency using systematic guidelines for public health surveillance system evaluation developed by the US Centers for Disease Control and Prevention. We assessed the system's overall performance in 5 main factors: timeliness, stability, completeness, sensitivity, and representativeness (ie, the age and geographic distribution of sentinels). We rated these factors as weak, moderate, or good. Results: Our study showed that the completeness, sensitivity, and age representativeness of the HFMD surveillance performance were temporarily reduced to moderate levels from 2020 to 2021 and recovered in 2022, while the timeliness and geographic representativeness were maintained at a good level throughout the study period. The stability of the surveillance was moderate from 2017 to 2021 and weak in 2022. Conclusions: This is the first study to evaluate the HFMD surveillance system after the acute phase of the COVID-19 pandemic. We identified a temporarily reduced level of performance (ie, completeness, sensitivity, and age-specific representativeness) during the acute phase of the pandemic and good performance in 2022. Surveillance system evaluation and maintenance during public health emergencies will provide robust and reliable data to support public health policy development. Regular staff training programs and reducing staff turnover will improve HFMD surveillance system stability.

Temporal Dynamics of Serum Perforin and Granzyme during the Acute Phase of SARS-CoV-2 Infection.

BACKGROUND: As many SARS-CoV-2 infections are asymptomatic, it could be useful to be able to determine how much time has passed since infection. We explored the changes in the temporal levels of T cell-related proteins (including perforin and granzymes) in the sera of patients with SARS-CoV-2 infection using a commercially available assay. METHODS: This study enrolled 36 patients infected with SARS-CoV-2 and 20 healthy control participants. Blood samples were collected at three different times based on the number of days since symptom onset (early phase: 1-5 days, mid-phase: 6-10 days, late phase: 11-18 days). We assessed the temporal changes in the serum levels of perforin and granzymes in patients with SARS-CoV-2 infection by comparing the results with those obtained in the healthy control group. RESULTS: We identified a significantly low level of perforin in the early phase of SARS-CoV-2 infection (p < 0.01), which was restored to normal during the mid- and late phases of the infection. However, there was no difference in the temporal change in the level of granzymes in SARS-CoV-2-infected patients compared to the healthy control group. CONCLUSIONS: This finding suggests that SARS-CoV-2 infection paralyzed the perforin expression in the early period immediately after infection. Thus, serum perforin is a potential marker for identifying the acute phase of SARS-CoV-2 infection.

Korea Seroprevalence Study of Monitoring of SARS-COV-2 Antibody Retention and Transmission (K-SEROSMART): findings from national representative sample.

OBJECTIVES: We estimated the population prevalence of antibodies to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), including unreported infections, through a Korea Seroprevalence Study of Monitoring of SARS-CoV-2 Antibody Retention and Transmission (K-SEROSMART) in 258 communities throughout Korea. METHODS: In August 2022, a survey was conducted among 10,000 household members aged 5 years and older, in households selected through two stage probability random sampling. During face-to-face household interviews, participants self-reported their health status, COVID-19 diagnosis and vaccination history, and general characteristics. Subsequently, participants visited a community health center or medical clinic for blood sampling. Blood samples were analyzed for the presence of antibodies to spike proteins (anti-S) and antibodies to nucleocapsid proteins (anti-N) SARS-CoV-2 proteins using an electrochemiluminescence immunoassay. To estimate the population prevalence, the PROC SURVEYMEANS statistical procedure was employed, with weighting to reflect demographic data from July 2022. RESULTS: In total, 9,945 individuals from 5,041 households were surveyed across 258 communities, representing all basic local governments in Korea. The overall population-adjusted prevalence rates of anti-S and anti-N were 97.6% and 57.1%, respectively. Since the Korea Disease Control and Prevention Agency has reported a cumulative incidence of confirmed cases of 37.8% through July 31, 2022, the proportion of unreported infections among all COVID-19 infection was suggested to be 33.9%. CONCLUSIONS: The K-SEROSMART represents the first nationwide, community-based seroepidemiologic survey of COVID-19, confirming that most individuals possess antibodies to SARS-CoV-2 and that a significant number of unreported cases existed. Furthermore, this study lays the foundation for a surveillance system to continuously monitor transmission at the community level and the response to COVID-19.

Temporal Dynamics of Serum Perforin and Granzymes in Three Different Clinical Stages of Virus-Induced Severe Fever with Thrombocytopenia Syndrome.

Virus-induced severe fever with thrombocytopenia syndrome (SFTS) induces a cell-mediated immune response that likely contributes to virus control in SFTS patients. To identify the temporal changes of the cell-mediated immune response, we investigated the changes in serum levels of perforin and granzymes at early periods after illness onset in SFTS patients. We analyzed 32 SFTS patients and compared the temporal patterns of serum perforin and granzyme A and B to that of 20 healthy control adults using the Mann-Whitney U test. Compared with healthy controls, the mean level of perforin was significantly reduced by 81% (P < 0.01) during the first week after illness onset, whereas granzyme B significantly increased by 4.6-fold (P = 0.02) in the first week after illness onset and decreased to normal afterward. During the study period, there was no significant difference in serum perforin and granzyme. These findings indicate that perforin and granzyme B in serum can be considered possible serologic markers that reflect the clinical stage of SFTS. Additional study is warranted for tracking circulating perforin and granzyme in different ages and for an extended period after illness onset.

The impact of the COVID-19 pandemic on chlamydia infection in South Korea: a comparison between the pre-pandemic and during-pandemic periods.

Background: Prior to COVID-19 pandemic, a yearly upward trajectory in the number of chlamydia infection cases was observed in South Korea. However, in response to the COVID-19 pandemic, Korea implemented several public health and social measures, which were shown to have an impact on the epidemiology of other infectious diseases. This study aimed to estimate the impact of the COVID-19 pandemic on the incidence and number of reported chlamydia infections in South Korea. Methods: Using the monthly number of reported chlamydia infection data between 2017 and 2022, we compared the trends in the reported numbers, and the incidence rates (IR) of chlamydia infection stratified by demographic characteristics (sex, age group, and region) in the pre- and during COVID-19 pandemic period (January 2017-December 2019 and January 2020-December 2022). Results: We observed an irregular downward trajectory in the number of chlamydia infection in the during-pandemic period. A 30% decrease in the total number of chlamydia infection was estimated in the during-pandemic compared to the pre-pandemic period, with the decrease greater among males (35%) than females (25%). In addition, there was a decrease in the cumulative incidence rate of the during COVID-19 pandemic period (IR: 0.43; 95% CI: 0.42-0.44) compared to the pre-pandemic period (IR: 0.60; 95% CI: 0.59-0.61). Conclusions: We identified decrease in the number of chlamydia infection during COVID-19 pandemic which is likely due to underdiagnosis and underreporting for the infection. Therefore, strengthening surveillance for sexually transmitted infections including chlamydia is warranted for an effective and timely response in case of an unexpected rebound in the number of the infections.

Association of public health and social measures on the hand-foot-mouth epidemic in South Korea.

BACKGROUND: School based-measures such as school closure and school holidays have been considered a viable intervention during the hand-foot-mouth disease (HFMD) epidemic. The aim of this study was to explore the association of nationwide public health and social measures (PHSMs) including planned school vacation on the transmissibility and attack rate of the HFMD epidemic in South Korea. METHODS: In this study, we used Korean national surveillance data on HFMD from 2014 to 2019 to estimate the temporal changes in HFMD transmissibility (instantaneous reproductive number, Rt). Furthermore, to assess the changes in the HFMD attack rate, we used a stochastic transmission model to simulate the HFMD epidemic with no school vacation and nationwide PHSMs in 2015 South Korea. RESULTS: We found that school vacations and 2015 PHSMs were associated with the reduced Rt by 2-7 % and 13 %, respectively. Model projections indicated school vacations and 2015 PHSMs were associated with reduced HFMD attack rate by an average of 1.10 % (range: 0.38-1.51 %). CONCLUSIONS: PHSMs likely have a larger association with reduced HFMD transmissibility than school-based measures alone (i.e. school vacations). Preventive measures targeting preschoolers could be considered as potential options for reducing the future burden of HFMD.

Correction: Relative bradycardia in patients with COVID-19.

[This corrects the article DOI: 10.1186/s42444-022-00073-z.].

Pediatric humoral immune responses and infection risk after severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and two-dose vaccination during SARS-CoV-2 omicron BA.5 and BN.1 variants predominance in South Korea.

Background: Humoral immune responses and infection risk after severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and coronavirus disease 2019 (COVID-19) vaccination during the Omicron BA.5 and BN.1 variants predominant period remains unexplored in pediatric population. Methods: We examined anti-spike (anti-S) immunoglobulin G (IgG) responses in a total of 986 children aged 4-18 years who visited outpatient clinics between June 2022 and January 2023, with a history of SARS-CoV-2 infection alone, completed two doses of COVID-19 vaccination alone, vaccine-breakthrough infection (i.e., infection after the single dose of vaccination), and no antigenic exposure. Furthermore, to determine SARS-CoV-2 infection risk, the incidence of newly developed SARS-CoV-2 infection was investigated up to March 2023. Results: The anti-S IgG levels in the 'vaccine-breakthrough infection' group exceeded those in the 'infection alone' and 'vaccination alone' groups (both P <0.01). Furthermore, the 'vaccination alone' group experienced more rapid anti-S IgG waning than the 'infection alone' and 'vaccine-breakthrough infection' groups (both P <0.01). We could not identify newly developed SARS-CoV-2 infection in the 'vaccine-breakthrough infection' group. Conclusion: Our findings suggest that hybrid immunity, acquired from SARS-CoV-2 infection and COVID-19 vaccination, was a potentially higher and longer-lasting humoral immune response and protected against SARS-CoV-2 infection in pediatric population during Omicron BA.5 and BN.1 variants predominant.

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.

Prediction of upcoming global infection burden of influenza seasons after relaxation of public health and social measures during the COVID-19 pandemic: a modelling study.

BACKGROUND: The transmission dynamics of influenza were affected by public health and social measures (PHSMs) implemented globally since early 2020 to mitigate the COVID-19 pandemic. We aimed to assess the effect of COVID-19 PHSMs on the transmissibility of influenza viruses and to predict upcoming influenza epidemics. METHODS: For this modelling study, we used surveillance data on influenza virus activity for 11 different locations and countries in 2017-22. We implemented a data-driven mechanistic predictive modelling framework to predict future influenza seasons on the basis of pre-COVID-19 dynamics and the effect of PHSMs during the COVID-19 pandemic. We simulated the potential excess burden of upcoming influenza epidemics in terms of fold rise in peak magnitude and epidemic size compared with pre-COVID-19 levels. We also examined how a proactive influenza vaccination programme could mitigate this effect. FINDINGS: We estimated that COVID-19 PHSMs reduced influenza transmissibility by a maximum of 17·3% (95% CI 13·3-21·4) to 40·6% (35·2-45·9) and attack rate by 5·1% (1·5-7·2) to 24·8% (20·8-27·5) in the 2019-20 influenza season. We estimated a 10-60% increase in the population susceptibility for influenza, which might lead to a maximum of 1-5-fold rise in peak magnitude and 1-4-fold rise in epidemic size for the upcoming 2022-23 influenza season across locations, with a significantly higher fold rise in Singapore and Taiwan. The infection burden could be mitigated by additional proactive one-off influenza vaccination programmes. INTERPRETATION: Our results suggest the potential for substantial increases in infection burden in upcoming influenza seasons across the globe. Strengthening influenza vaccination programmes is the best preventive measure to reduce the effect of influenza virus infections in the community. FUNDING: Health and Medical Research Fund, Hong Kong.

Estimating the incubation period of SARS-CoV-2 Omicron BA.1 variant in comparison with that during the Delta variant dominance in South Korea.

Based on exposure history and symptom onset of 22 Omicron BA.1 cases in South Korea from November to December 2021, we estimated mean incubation period of 3.5 days (95% CI: 2.5, 3.8), and then compared to that of 6.5 days (95% CI: 5.3, 7.7) for 64 cases during Delta variants' dominance in June 2021. For Omicron BA.1 variants, we found that 95% of symptomatic cases developed clinical conditions within 6.0 days (95% CI: 4.3, 6.6) after exposure. Thus, a shorter quarantine period may be considered based on symptoms, or similarly laboratory testing, when Omicron BA.1 variants are circulating.