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Background: In South Korea, COVID-19 vaccination has been recommended to adolescents aged 12 − 17 since October, 2021. We aimed to assess the rate of adverse events following COVID-19 vaccination in adolescents with chronic kidney disease (CKD) in South Korea, using national cohort data. Methods: We retrieved the clinical information of adolescents 12 − 17 years old from the Korea Disease Control and Prevention Agency-COVID19-National Health Insurance Service (K-COV-N) database, to calculate incidence rates of purpura and other hemorrhagic conditions, Guillain-Barré syndrome (GBS), Kawasaki disease/multisystem inflammatory syndrome in children (MIS-C), myocarditis and/or pericarditis, and anaphylaxis in adolescents with CKD, after BNT162b2 vaccination. Results: Among the 2306 adolescents with CKD, 62.7% (n = 1446) had received the BNT-162b2 vaccine. GBS, Kawasaki disease/MIS-C, and anaphylaxis or anaphylactic shock did not occur during the observation period. Purpura and hemorrhagic conditions were more frequent in the unvaccinated group (7/860 vs. 1/1446), while myocarditis/pericarditis was observed only in the vaccinated group (0/860 vs. 1/1446). Adjusted odds ratio for any of the two adverse events was lower in vaccinated adolescents than in the unvaccinated group which did not reach statistical significance (adjusted odds ratio = 0.14, 95% confidence interval: 0.02, 1.16, P = 0.068). Conclusions: In this national cohort study of adolescents with CKD in South Korea, we observed no evidence of increased risk of adverse events following BNT162b2 vaccination. Our finding offers insights into the safety of COVID-19 vaccines, empowering adolescent patients with CKD and their caregivers to make informed decisions. [ABSTRACT FROM AUTHOR]

Background Despite the general consensus on the safety of pneumococcal conjugate vaccine (PCV), safety concerns unveiled during post-licensure surveillance need to be addressed. We investigated whether there is a transient increased risk following a three-dose series of pneumococcal conjugate vaccine (PCV) administered at 2, 4 and 6 months of age. Methods This was a population-based cohort study using the Korea immunization registry data linked to nationwide administrative claims data. Self-controlled risk interval analysis was conducted for PCV recipients who had an outcome of interest within pre-defined risk and control intervals between 2018 and 2022. The outcomes were anaphylaxis, asthma, encephalopathy, febrile seizure, Kawasaki disease and thrombocytopenia. We used conditional Poisson regression model to estimate the incidence rate ratios (IRRs) and 95% confidence intervals (CIs) comparing the outcomes in the risk and control intervals. Results Of 1 114 096 PCV recipients, 8661 had outcomes either in the risk or control intervals. Their mean age at Dose 1 was 10.0 weeks, 58.3% were boys, and 85.3% received 13-valent PCV. PCV was not associated with an increased risk of any outcomes except for febrile seizure. There were 408 (56.0%) cases of febrile seizure in the risk interval, corresponding to an IRR of 1.27 (95% CI 1.10–1.47). Conclusions It is reassuring to note that there was no increased risk of the potential safety concerns following PCV administration. Despite the transient increased risk of febrile seizure, absolute numbers of cases were small. Febrile seizure is generally self-limiting with a good prognosis, and should not discourage parents or caregivers from vaccinating their children. [ABSTRACT FROM AUTHOR]

Two live attenuated varicella vaccine (VZV) strains have been mainly used across the globe: MAV/06 and OKA strains. We aimed to explore the safety of interchanging the two VZV strains for primary and booster immunizations. South Korea's vaccine adverse event reporting system (VAERS) was accessed and searched to find filed reports of all adverse events (AEs) following immunization with the second dose of the varicella vaccine. The electronic medical records were reviewed for all visits to the hospital following the second dose of the varicella vaccine. Of the total 406 study participants, 27.5% (n = 112) were in the MAV/06–MAV/06 group, 30.3% (n = 123) in the MAV/06–OKA, 17.5% (n = 71) in the OKA–MAV/06 group, and 24.6% (n = 100) in the OKA–OKA group. Mean age at immunization with the first dose was 1.10 (standard deviation [SD] ±0.34) years old, and second dose was 4.77 (SD ± 1.13) (p = 0.772 and 0.933, respectively). There were no filed reports of AEs following the second dose in the national VAERS. Hospital visit records showed a total of 10.3% (95% confidence interval [CI], 7.6–13.7) (n = 42) had recorded AEs following the 2nd administered dose; however, only 0.7% (95% CI, 0.2–2.4) (n = 3) were regarded as possibly vaccine related. Two patients in the MAV/06–OKA group were diagnosed with Henoch-Schonlein purpura after the second dose; however, both had also received the MMR vaccine on the same day. No safety signals associated with interchanging the MAV/06 and OKA strain live attenuated varicella vaccines were observed in this patient cohort of healthy children. [ABSTRACT FROM AUTHOR]

To better understand the epidemiology of SARS‐CoV‐2 reinfections, we analyzed national data from South Korean who were followed longitudinally from January 2020 to April 2022. We conducted a nationwide retrospective cohort study to estimate possible SARS‐CoV‐2 reinfection rates in all residents in South Korea, with at least two episodes of laboratory‐confirmed SARS‐CoV‐2 infection by reverse‐transcriptase polymerase chain reaction or rapid antigen test (RAT) performed at least 45 or more days between both episodes, between January 2020 and April 2022. There were 16 130 855 laboratory‐confirmed SARS‐CoV‐2 cases in South Korea, with 55 841 (346.2 per 100 000; or 0.3% of all infections) cases of possible reinfections. The reinfection rate has increased from 6.0 cases per 100 000 during Pre‐Delta period to 128.0 cases per 100 000 and 355.1 cases per 100 000 during Delta and Omicron periods, respectively. Persons with one dose of vaccination had the highest reinfection rate of 642.2 per 100 000, followed by unvaccinated persons (536.2/100 000) and two‐dose vaccinated persons (406.3/100 000). Our finding suggests that the majority of possible reinfections occurred following the emergence of new variants. [ABSTRACT FROM AUTHOR]

Summary: Background: The global prevalence of inflammatory bowel disease (IBD) is increasing. However, population‐level data are scarce for Asian populations. Aims: To outline and compare paediatric and adult IBD incidence and prevalence data in Korea, describe prescription patterns, and analyse outcomes of anti‐tumour necrosis factor (anti‐TNF) use in a nationally representative cohort Methods: IBD was identified based on the presence of Rare and Intractable Disease diagnosis codes for Crohn's disease (CD) and ulcerative colitis (UC). We calculated age‐based prevalence and incidence, and examined prescription patterns. We used a Cox proportional hazard model to calculate the hazard ratio (HR) for undergoing surgery. Results: The prevalence of CD increased between 2006 and 2015, particularly among those aged 10–19 years (12.7–35.5 patients per 100,000 people). The use of anti‐TNF agents increased from 3.2% to 22.9% in paediatric CD patients. Early use of an anti‐TNF agent increased 25‐fold in CD patients. Further, CD patients aged 0–14 years were most likely to undergo fistulectomy (HR, 2.63; 95% confidence interval [CI], 1.73–3.97). Children with UC had a higher risk of undergoing surgery (HR, 3.01; 95% CI, 1.33–6.83) than adults. Early use of an anti‐TNF agent in CD patients was associated with lower odds of surgery than late‐stage use. Conclusion: The prevalence of IBD has increased over time, especially among paediatric patients. Given the magnitude of paediatric IBD disease burden, a multi‐faceted approach is needed for early detection and vigilant monitoring to aim for better prognosis. [ABSTRACT FROM AUTHOR]

Introduction: TETRAXIM™ (Sanofi), a combined diphtheria, tetanus, acellular pertussis, and inactivated poliovirus (DTaP-IPV) vaccine, has been licensed in South Korea since 2009. In accordance with the Ministry of Food and Drug Safety regulations, this post-marketing surveillance (PMS) study evaluated the safety of the DTaP-IPV vaccine in real-world clinical practice in infants and children who received it as either a part of the three-dose primary series dose at 2, 4, and 6 months or school entry booster between 4 and 6 years of age. Methods: This multicenter, observational, PMS study was conducted in real-world practice in South Korea for 6 years (2009–2015) in participants aged between 2 months and 6 years. The study outcomes included solicited reactions, unsolicited adverse events (AEs)/adverse drug reactions (ADRs), unexpected AEs/ADRs, and serious AEs (SAEs)/ADRs. Results: Data from 647 participants was included in the safety analysis. Overall, 268 AEs were reported by 181 (28%) participants: 47 (17.5%) solicited reactions, 220 (82.1%) unsolicited AEs, and 1 (0.4%) unsolicited ADR. A total of 48 AEs (including 47 solicited reactions) were reported to have a causal relationship with the DTaP-IPV vaccine and were reported by 36 (5.6%) participants. A total of 212 unexpected AEs were reported by 152 (23.5%) participants, none of which had a causal relationship with the DTaP-IPV vaccine. Neither immediate AEs nor SAEs were reported during the study. Among the participants who reported AEs, 220 (34%) were on concomitant medications. Most AEs were of mild intensity, and all participants recovered. Conclusion: No safety concerns related to the DTaP-IPV vaccine in a real-world setting were raised in participants aged 2–6 months for the primary series and 4–6 years for the school-entry booster dose in the Korean population. The DTaP-IPV vaccine was well tolerated and can be continued as part of routine immunization programs in infants and children. Trial Registration: NCT01437423. [ABSTRACT FROM AUTHOR]

We evaluate the overall effectiveness of the nationwide vaccination campaign using ChAdOx1 nCoV-19, BNT162b2, mRNA-1273, and Ad26.COV2.S vaccines in preventing Covid-19 in South Korea. The National Surveillance System with the National Immunization Registry were linked to form a large-linked database for assessment. Age-adjusted incidence of SARS-CoV-2 infection, severe disease, and death by vaccination status are calculated. Weekly vaccine effectiveness was calculated based on incidence rate ratio (IRR) between fully-vaccinated and unvaccinated persons, as: IRR = incidence rate of vaccinated / incidence rate of unvaccinated. We estimate the cumulative SARS-CoV-2 outcome overtime comparing the observed case with predicted cases without vaccination. Age-adjusted incidence in unvaccinated persons (5.69 per 100,000 person-day) was 2.7 times the rate in fully vaccinated (2.13 per 100,000 person-day) persons, resulting effectiveness against SARS-CoV-2 infection of 63%. Vaccine effectiveness against severe disease and death were 93% and 95%, respectively. Between March and October 2021, estimated Covid-19 related outcomes averted by vaccinations were: 46,508 infections, 3,424 severe diseases, and 718 deaths. We found significant protection for national Covid-19 vaccination campaign against Covid-19 severe disease, and death in target populations, but there was an unexpected decreased protection against SARS-CoV-2 infection, highlighting the importance of continued surveillance and assessment. [ABSTRACT FROM AUTHOR]

Background The immunologic features of children with coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are not clearly delineated. This study was conducted to evaluate SARS-CoV-2-specific antibody responses in children with COVID-19. Methods The levels of anti-spike (S) IgG, anti-SARS-CoV-2 IgG, and neutralizing antibody (NAb) were measured during various time points in children <19 years of age with COVID-19 in South Korea from February 2020 to September 2020. Results One hundred sixty-five blood samples from 114 children with COVID-19 (43.9% asymptomatic and 56.1% mildly symptomatic) were analyzed. In both asymptomatic and mildly symptomatic children, the positive rates of anti-S IgG, anti-SARS-CoV-2 IgG, and NAb were low within 7 days after onset, but they soon reached 100% 14 to <28 days after onset. In symptomatic children, the geometric mean titers (GMTs) of antibodies were all below the positive cutoff during the first 2 weeks from onset and peaked at 28 to <56 days (5.6 for anti-S IgG, 383.6 for anti-SARS-CoV-2 IgG, and 55.0 for NAb, P <.001, respectively). Antibody levels remained detectable up to 3 months after infection. The antibody GMTs during the period 14 to <56 days after symptom onset were highest in children aged 0-4 years. Conclusions These results collectively present the humoral immune responses during SARS-CoV-2 infection in children. A further longitudinal study is needed to thoroughly understand the immune system and for effective vaccine development in children during the COVID-19 pandemic. [ABSTRACT FROM AUTHOR]

Objective: There is an urgent public need to readdress the school closure strategies. We aimed to describe the epidemiology of COVID-19 in schools and school-aged children to understand their roles in transmitting SARS-CoV-2 in Korea.Design: Retrospective cohort study.Setting: All schools in Korea PATIENTS: All school-aged children in Korea.Interventions: None (observational study).Main Outcome Measures: Incidence rate, proportion of affected schools.Results: Between February and December 2020, the incidence rate was lower among school-aged children (63.2-79.8 per 100 000) compared with adults aged 19 and above (130.4 per 100 000). Household was the main route of transmission (62.3%), followed by community (21.3%) and school clusters (7.9%). Among the schools in Korea, 52% of secondary schools had COVID-19 cases, followed by 39% of primary schools and 3% of kindergartens.Conclusions: We found that schools and school-aged children aged 7-18 years were not the main drivers of COVID-19 transmission. The major sources of transmission were households. [ABSTRACT FROM AUTHOR]

Varicella is a highly contagious disease caused by the varicella‐zoster virus (VZV). Given its tendency to cluster geographically, spatial analyses may provide a better understanding of the pattern of varicella transmission. We investigated the spatial characteristics of varicella in Korea and the risk factors for varicella at a national level. Using national surveillance and demographic data, we examined the spatial distribution of incidence rates and their spatial autocorrelation and calculated Moran's index. Spatial regression analysis was used to identify sociodemographic predictors of varicella incidence at the district level. An increasing tendency in the annual incidence of varicella was observed over a 12‐year period (2006–2018), with a surge in 2017. There was a clear positive spatial autocorrelation of the varicella incidence rate during the surveillance period. During 2006–2014, High‐High (HH) clusters were mostly confined to the northeast region and neighboring districts. The spatial error model showed that population density had a negative coefficient and childhood percentage, percentage of children under 12 years of age among the total population, had positive coefficient, whereas vaccine coverage was insignificant. The varicella incidence according to geographic region varied with population density, childhood percentage, suggesting the importance of community‐level surveillance and monitoring strategies. Highlights: The incidence of varicella in Korea showed a temporal uptrend from 2006 to 2018 with a clear seasonal pattern.The local spatial clusters of "hot‐spots" occurred in remote rural areas during the early surveillance period and gradually scattered and faded.In the spatial regression analysis, sociodemographic predictors such as childhood percentage had a positive effect on the incidence, whereas population density and number of hospitals per 1000 persons had negative effects. [ABSTRACT FROM AUTHOR]

Background Nonsteroidal antiinflammatory drugs (NSAIDs) may exacerbate coronavirus disease 2019 (COVID-19) and worsen associated outcomes by upregulating the enzyme that severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) binds to in order to enter cells. Methods We conducted a cohort study using South Korea's nationwide healthcare database, which contains data for all individuals who received a COVID-19 test (n = 69 793) as of 8 April 2020. We identified adults hospitalized with COVID-19, where cohort entry was the date of hospitalization. NSAID users were those prescribed NSAIDs in the 7 days before and including cohort entry, and nonusers were those not prescribed NSAIDs during this period. Our primary outcome was a composite of in-hospital death, intensive care unit admission, mechanical ventilation use, and sepsis; our secondary outcomes were cardiovascular complications and acute renal failure. We conducted logistic regression analysis to estimate odds ratio (OR) with 95% confidence intervals (CIs) using inverse probability of treatment weighting to minimize confounding. Results Of 1824 adults hospitalized with COVID-19 (mean age, 49.0 years; female, 59%), 354 were NSAID users and 1470 were nonusers. Compared with nonuse, NSAID use was associated with increased risks of the primary composite outcome (OR, 1.54; 95% CI, 1.13–2.11) but insignificantly associated with cardiovascular complications (OR, 1.54; 95% CI, 0.96–2.48) or acute renal failure (OR, 1.45; 95% CI, 0.49–4.14). Conclusions While awaiting the results of confirmatory studies, we suggest NSAIDs be used with caution for COVID-19 patients as the harms associated with their use may outweigh their benefits. [ABSTRACT FROM AUTHOR]

Background: We hypothesized that nationwide social distancing and other preventive measures for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) were associated with reduced detection of other respiratory viruses in South Korea.Methods: We analyzed national surveillance data to compare incidence of respiratory viruses during 2016-2019 vs 2020. Results of multiplex reverse-transcription polymerase chain reaction assays for 8 respiratory viruses were included: adenovirus (ADV), parainfluenza virus (PIV), respiratory syncytial virus (RSV), influenza virus (IFV), human coronavirus (HCoV; non-SARS-CoV-2), human rhinovirus (HRV), human bocavirus (HBoV), and human metapneumovirus (HMPV).Results: During 2016-2019, rates of detection of respiratory viruses were relatively stable: ADV, 3.7%-9.2%; PIV, 1.4%-17.0%; RSV, 0.3%-15.3%; IFV, 0.4%-35.6%; HCoV, 1.5%-8.4%; HRV, 7.0%-25.1%; HBoV, 0.6%-6.3%; and HMPV, 0.7%-14.5%. Following implementation of social distancing in February 2020, rates of detection of enveloped viruses (HCoV, HMPV, IFV, PIV, and RSV) were significantly reduced by up to 100%. However, nonenveloped viruses (ADV, HRV, and HBoV) persisted throughout 2020, and HRV rates in hospitalized patients significantly increased.Conclusions: After implementation of social distancing for SARS-CoV-2 in South Korea, rates of detection of enveloped respiratory viruses decreased significantly, whereas nonenveloped viruses persisted, suggesting that enhanced infection prevention strategies are required to mitigate spread of these viruses. [ABSTRACT FROM AUTHOR]

• Pneumococcal carriage rate has increased from 36.4% in 2014 to 42.1% in 2019 • NTHi carriage rate has decreased from 36.5% in 2014 to 26.7% in 2019 • Among children carrying pneumococci, a significant increase was in serotype 23A • Children who received PCV had lower risk of vaccine-type carriage Nasopharyngeal (NP) colonization with Streptococcus pneumoniae and non-typeable Haemophilus influenzae (NTHi) is common in children, and may evolve as the source of invasive infections. In Korea, the pneumococcal conjugate vaccines (PCVs) were introduced >10 years ago, enabling the authors to study the effect of the vaccine in preventing carriage. NP swabs were taken and a household survey was conducted at daycare centres located in different regions of Korea in 2014 and 2019. Pneumococcal serotypes were identified using the Quellung method and sequencing. NTHi were identified based on pilA and bexA genes. In total, 1460 NP swabs were obtained with pneumococcal carriage rates of 36.4–42.1% and NTHi carriage rates of 36.5–26.7%. Among children carrying pneumococci, a significant increase was seen in serotype 23A between 2014 and 2019 (from 12.6% to 22.0%; P =0.005). Children who had received PCV were at lower risk of vaccine-type carriage (2.9% vs 0.8%; P =0.005). Between 2014 and 2019, the proportion of children carrying serotype 23A increased significantly, while the carriage rate of NTHi decreased. Continuous surveillance is needed to assess the long-term effects of the PCVs on carriage dynamics of pneumococcus and NTHi. [ABSTRACT FROM AUTHOR]

Keywords: elimination; measles; rash; vaccine; VARI EN elimination measles rash vaccine VARI 4539 4541 3 07/15/22 20220901 NES 220901 INTRODUCTION Globally, annual measles incidence decreased 79%, from 36 763 000 in 2000 to 7 549 000 in 2020; while estimated measles-containing vaccine (MCV) immunization coverage increased from 72% to 84%.1 In the progress toward measles elimination, a strong virologic surveillance is essential to document the interruption of transmission of measles virus.2 In the setting of low-incidence, many places report measles vaccine-associated rash illness (VARI) among the suspected measles case-patients.3 The World Health Organization (WHO) definition for VARI include criterion with rash illness, with or without fever; that began 7-14 days after vaccination; and serological documentation of acute measles infection; while, alternatively, a suspected case from which virus was isolated and found on genotyping to be a vaccine strain (genotype A).4 Clinically, VARI is often a mild illness which does not usually require medical attention in immunocompetent hosts, however, may pose confusion to the surveillance and may add the unnecessary burden on the public health system, when the incidence of measles is low.5 Yet, the magnitude of VARI is not clearly understood, to date. 77.3% (85/110) of the VARI case-patients had their rash onset after 9-13 days of MCV immunization (Figure 1), with a mean interval of 10 days (1-17 days, Table 1). 86.4% had fevers, while 20.0%, 24.5% had cough and coryza, respectively (Table 1). 2.7% of VARI case-patients had conjunctivitis. RESULTS Between 2011 and 2021, a total of 841 (88.4%) wild-type (laboratory-confirmed) measles and 110 (11.6%) VARI case-patients were notified in South Korea. [Extracted from the article]

A concerning development during the coronavirus disease pandemic has been multisystem inflammatory syndrome in children. Reports of this condition in East Asia have been limited. In South Korea, 3 cases were reported to the national surveillance system for multisystem inflammatory syndrome in children. All case-patients were hospitalized and survived with no major disease sequelae. [ABSTRACT FROM AUTHOR]

• Approaches to prevent congenital rubella syndrome are: (1) vaccination of young women, (2) vaccination of infants, and (3) combination of the two. • There was a staged introduction of RCV among teenage girls and universal two-dose MMR programs in targeted cohorts in Korea. • Both cohort who were the target of vaccination for adolescent girls and those of combined strategy showed lower susceptibility to rubella. The aim was to examine rubella seronegativity among women of childbearing age after the introduction of rubella-containing vaccine (RCV) among teenage girls and universal MMR programs in South Korea. The serum IgG data of 72 114 women aged 20–49 years, who had undergone rubella antibody testing at the Gangnam CHA Medical Center between 2004 and 2018, were examined. A serum IgG level <10.0 IU/ml was considered negative. The study population was divided into three cohorts based on the vaccination policy: cohort 1, 1955–1976 (no national immunization program); cohort 2, 1977–1985 (national rubella only vaccination for high schoolers); cohort 3, 1986–1993 (combination strategy). We compared the rate of seronegativity and the adjusted odds ratio (OR) of seronegativity of each cohort. The overall proportion of seronegative women decreased significantly, from 6.1% in 2004 to 2.5% in 2018 (Kendall tau = −0.89, p < 0.001). The rate of seronegativity was highest among women who were not targeted for national immunization (born in 1955–1977, 5.2%), while it was lowest among candidates receiving routine and catch-up vaccinations (born in 1986–1993, 2.2%). When controlling for the effect of age and year of testing, the OR for seronegativity was lower for cohort 2 (adjusted OR 0.68, 95% confidence interval (CI) 0.60–0.76) and cohort 3 (OR 0.55, 95% CI 0.40–0.75) when compared to cohort 1. Women who were covered by either vaccination program were less susceptible to rubella infection, supporting the value of both approaches. The study findings will serve as empirical evidence for an immunization program targeted towards young women and children. [ABSTRACT FROM AUTHOR]

• Japanese encephalitis causes high disease burden in endemic countries. • Introduction of vaccine has significantly reduced the incidence in Korea. • Change of epidemiology was noted: potentially from virus genotype, vector mosquito, and amplifying hosts. Japanese encephalitis (JE) is endemic in the Western Pacific Region. We aim to describe the regional status of control of JE, based on the World Health Organization (WHO) surveillance data, and to share the experience from the Republic of Korea. Substantial progress has been made in the region to date; however, epidemiologic changes have not been delineated. The vaccination coverage should be addressed to close the immunity gap. The lessons learned from Korea may aid in establishing a high-quality surveillance system with a sustainable JE vaccination program in order to prepare for new challenges that this region will face. [ABSTRACT FROM AUTHOR]

Aims:Acinetobacter baumannii has become an important nosocomial pathogen that causes invasive infections. We conducted a retrospective study to evaluate the risk factors for mortality due to A. baumannii bacteremia in children. Materials and Methods: We reviewed data from Seoul National University Children's Hospital from 2002 to 2013 for children with A. baumannii bacteremia, including age, gender, underlying disease, associated site of infection, duration of hospitalization, presence of neutropenia, and antibiotic susceptibility data. The outcome measures were the 7- and 30-day mortality rates. Results: Among 74 A. baumannii bacteremia cases, 35.1% were carbapenem nonsusceptible. Common comorbidities were malignancy or hematologic diseases (28.4%), followed by gastrointestinal/hepatobiliary diseases (21.6%). A total of 47.3% of patients had isolated bacteremia, and in 33.8% of patients, pneumonia accompanied bacteremia. The mortality rates were 18.9% at 7 days and 35.1% at 30 days. The significant associated factors for 30-day mortality were carbapenem nonsusceptibility (adjusted hazard ratio [aHR]: 1.28, 95% confidence interval [CI]: 1.10–11.82, p = 0.034), neutropenia (aHR: 1.68, 95% CI: 1.60–18.03, p = 0.007), and prior intensive care unit (ICU) admission (aHR: 1.15, 95% CI: 1.03–9.73, p = 0.045). The mortality rate among neutropenic patients with inappropriate empirical antibiotics was higher than that among patients with appropriate empirical antibiotics (90.1% vs. 33.3%, p = 0.031). Conclusions: We identified carbapenem nonsusceptibility, neutropenia, and prolonged ICU stay as independent risk factors for mortality due to A. baumannii bacteremia in children. An early administration of appropriate antibiotics should be enacted, especially in patients with neutropenia. [ABSTRACT FROM AUTHOR]

While vaccination remains the cornerstone of controlling vaccine‐preventive diseases (VPD), little is known about the effect of social distancing on incidence of VPDs. We investigated the impact of social distancing practiced during the coronavirus disease 2019 (COVID‐19) pandemic on the incidence of selected VPDs in South Korea. National surveillance data on monthly incidence of hepatitis A, hepatitis B, varicella, mumps, invasive pneumococcal disease (IPD), and pertussis were retrieved and compared the VPD incidences in 2020 to the average of the last 4 years (2015–2019) of the corresponding months. In 2020, there were 44% decline for mumps, 44% decline for varicella, 28% decline for pertussis, 22% decline for IPD, 14% decline in incidence of hepatitis A, and no change for hepatitis B incidences, compared to baseline years (2015–2019). The largest decline of total VPDs was in April (65%) and in May (67%), during the intensified social distancing measures. In the setting of sustained vaccination coverage, social distancing may provide additional public health benefit in controlling the VPDs. [ABSTRACT FROM AUTHOR]

Keywords: coronavirus; epidemiology; seasonal incidence EN coronavirus epidemiology seasonal incidence 585 587 3 01/01/21 20210201 NES 210201 Despite advances in our understanding of the pathogenesis of Kawasaki disease, its association with respiratory viruses remains unclear. GLO:OCQ/01feb21:jmv26435-fig-0001.jpg PHOTO (COLOR): 1 Monthly frequency of Kawasaki disease patients and the proportion of coronavirus detected in the national surveillance samples, South Korea, 2016 to 2019. We observed a no association between HCoVs and Kawasaki disease, which demonstrates no potential epidemiological linkage to explain the pathogenesis of Kawasaki disease. [Extracted from the article]

Abstract: Background: Antimicrobial resistance is a concern to public health, and controlling antibiotic use is therefore important. This study analyzed the trend in outpatient antibiotic prescriptions in children and adolescents in Korea. Methods: Using National Prescribing Sample data from the Korea Health Insurance Review and Assessment Service between 1 January 2010 and 31 December 2014, we analyzed outpatient systemic antibiotic (anatomical therapeutic chemical [ATC] J01) prescriptions in patients aged 2–17 years. The antibiotic rate was defined as the proportion of all outpatient prescriptions for antibiotics. We calculated absolute and relative differences with 95%CI between 2010 and 2014 in the antibiotic rate by age group (2–6, 7–11, and 12–17 years) and the percentage of antibiotic prescriptions by antibiotic class. Seven of the most commonly used antibiotic drugs were identified based on defined daily dose. Results: A total of 7 261 176 prescriptions were written for 1 039 756 pediatric patients between 2010 and 2014. The antibiotic rate in all patients increased from 34.8% in 2010 to 70.4% in 2014, resulting in the relative difference of 102.1% (95%CI: 101.7–102.5). Extended spectrum penicillins were the most commonly prescribed antibiotic class, accounting for 40.0–41.0% of all antibiotic prescriptions. The use of third‐generation cephalosporins increased steeply with the relative difference of 55.7% (95%CI: 55.2–56.2). Amoxicillin/clavulanate, an extended spectrum antibiotic drug, was the predominately used antibiotic drug but the use of cefpodoxime, a third‐generation cephalosporin, increased by 96%. Conclusions: The use of outpatient antibiotics, especially third‐generation cephalosporins, has increased in children and adolescents in Korea. [ABSTRACT FROM AUTHOR]

Background Countries with strong vaccination programmes, including the Republic of Korea, have experienced changes in the epidemiology of Japanese encephalitis (JE), with an increase in cases seen among adults. However, the reasons for this increase are not clearly understood. This study describes the change in age-specific JE virus (JEV) seroprevalence over time in Korea, with a view to understanding this transition. Methods A search of Embase, MEDLINE, PubMed, KoreaMed, Korea Education and Research Information Service, National Library of Korea, and the Seoul National University Medical Library was conducted using the keywords ‘Japanese encephalitis’ combined with ‘Korea’, ‘seroprevalence’, ‘seropositivity’, ‘seroepidemiology’, ‘serosurvey’, ‘immunity’, and ‘antibody’. Results Eighteen studies published between 1946 and 2012 were retrieved. In 1946, seropositivity was 51% in the 1–10 years age group, 79% in those aged 11–20 years, and 94% in those ≥61 years of age. In the 1970s, seropositivity in children and adolescents was low (10–59%); seropositivity in this group increased to 90–92% in 1984–1985, and increased further to 98% in 2012. Seropositivity among adults aged 41–50 years and 51–60 years in the 2010s ranged between 83.1% and 97.9% and between 77.5% and 98.3%, respectively. Conclusions The implementation of the universal JE vaccination programme in the 1980s has increased the seroprevalence of JEV in Korea, especially in children who are targeted for vaccination. [ABSTRACT FROM AUTHOR]

We used national statistics from 1983-2015 to evaluate trends in mortality caused by infectious diseases in South Korea. Age-standardized mortality from infectious disease decreased from 43.5/100,000 population in 1983 to 16.5/100,000 in 1996, and then increased to 44.6/100,000 in 2015. Tuberculosis was the most common cause of death in 1983 and respiratory tract infections in 2015. We observed a significant decline in infant deaths caused by infectious diseases, but mortality in persons age >65 years increased from 135 deaths/100,000 population in 1996 to 307/100,000 in 2015. The relative inequality indices for respiratory tract infections, sepsis, and tuberculosis tended to increase over time. Although substantial progress has been achieved in terms of infant mortality, death rates from infectious disease has not decreased overall. Elderly populations with lower education levels and subgroups susceptible to respiratory infections and sepsis should be the focus of preventive policies. [ABSTRACT FROM AUTHOR]

• Historically, hepatitis A incidence has been higher in males compared to females. • Since 2012, hepatitis A vaccine has been provided to military recruits. • Difference in incidence between females and males has been narrowed. • In 2019 among young adults, the incidence was lower in males compared to females. We examined the trend in gender difference for hepatitis A incidence in South Korea after introducing universal vaccination in toddlers and in military recruits. We found that the male-female incidence rate ratio has decreased significantly especially among persons aged 20–29 years, suggesting additional impact from vaccinating military recruits. [ABSTRACT FROM AUTHOR]

Background This study was performed to determine the priority of vaccine introduction for five vaccine-preventable diseases (VPDs) caused by Haemophilus influenzae type b (Hib), pneumococcus (Spn), hepatitis A virus (HepA), rotavirus (RV), and human papillomavirus (HPV) to the future Korean National Immunization Program (NIP) and to suggest framework programs to assist decision makers on implementation of the NIP. Methods Following analysis of the disease burden and economics of the five VPDs by the core team and Korean Advisory Committee on Immunization Practices sub-committee members, a Delphi survey was administered to 94 Korean experts using structured questionnaires that provided the reference data. The two evaluation frameworks for NIP prioritization were (1) a disease-related framework and (2) a vaccine-related framework. After analyzing the responses, a meeting of experts was held to build a consensus for determining how to prioritize NIP implementation. Results The average scores for relative importance were 63.29 for the disease-related framework and 36.71 for the vaccine-related framework. Within the disease-related framework, the mortality and case fatality rate was the highest scored factor (8.97), whereas within the vaccine-related framework, efficacy of the vaccine was considered the most important factor (9.56). On average, Spn, Hib, and HepA had the highest priority scores. Conclusion The Korean experts suggested that the main factors influencing the decision to adopt new vaccines in the Korean NIP should be disease mortality, case fatality, and the efficacy and effectiveness of the vaccine. Among the five selected VPDs, Spn, Hib, and HepA were considered to be of higher priority than RV and HPV. [ABSTRACT FROM AUTHOR]

Highlights: [•] We modeled four measles vaccination strategies and compared cost–benefit ratio. [•] With catch-up campaign, baseline 178,560 measles cases would decrease to 5936. [•] Two-dose MMR and MR catch-up campaign showed the highest cost–benefit ratio. [ABSTRACT FROM AUTHOR]

Abstract: Background: There is concern about a possible association between influenza A(H1N1)pdm09 vaccination and narcolepsy. In this study, we assessed the incidence and incidence rate of narcolepsy in the South Korean population before and after the implementation of an A(H1N1)pdm09 vaccination campaign to see if vaccination led to a change in the occurrence of narcolepsy. Methods: We conducted an ecological study, comparing incident cases and incidence rates for newly diagnosed narcolepsy case-patients in South Korea, between July 2006 and June 2011. We used data from the Health Insurance Review Agency and Korea Centers for Disease Control and Prevention, which have limited information on case ascertainment. During vaccination campaign period, South Korea used non-adjuvanted and MF59-adjuvanted A(H1N1)pdm09 vaccines. Results: Generally, incidence rate was highest in prepandemic period. No trend toward increase in the incidence of narcolepsy after pandemic period was found. Observation of incidence by season did not suggest any time pattern for occurrence of narcolepsy. Conclusion: No increase in cases or incidence rate for narcolepsy during the A(H1N1)pdm09 vaccination campaign was found in South Korea. Our data do not support the use of MF59-adjuvanted or non-adjuvanted A(H1N1)pdm09 vaccine as a trigger for narcolepsy on a population level. [Copyright &y& Elsevier]

Background: Because the peak age for incidence of sudden deaths in infancy temporally coincides with the age of infant primary immunization, some have raised the question as to whether immunization is a risk factor for sudden death in infancy. Recent occurrence of two sudden deaths in infants in Korea has renewed concerns about the causal association between immunization and sudden deaths in infants. Methods: We carried out a retrospective review of data from the Korea Centers for Disease Control and Prevention Adverse Events Following Immunization Surveillance System and Vaccine Compensation programs. Results: From 1994 to 2011, a total of 45 cases of sudden deaths in the first 2 years of life following immunization were reported in Korea. The causes of death were classified as follows: infectious diseases ( n= 13); accidental injuries ( n= 7); congenital abnormalities ( n= 2); and malignancy ( n= 1). Of 20 sudden deaths in infancy, nine deaths met Brighton Collaboration case definition level I and II, and therefore were classified as possible sudden infant death syndrome cases. Hepatitis B vaccine ( n= 13) was the most frequent vaccine with temporal association with sudden deaths in the first 2 years of life. Conclusion: Few sudden deaths in the first 2 years of life following immunization have been reported, despite the use of universal immunization in Korea. The majority of deaths in infancy did not meet case definition for sudden infant death syndrome. Encouraging investigators to perform thorough investigation, including postmortem autopsy and death scene examination, may promote data comparability and provide guidance on decision-making in the vaccine-safety monitoring and response system in Korea. [ABSTRACT FROM AUTHOR]

This study investigated the infectivity of severe acute respiratory syndrome (SARS-CoV-2) in individuals who re-tested positive for SARS-CoV-2 RNA after recovering from their primary illness. We investigated 295 individuals with re-positive SARS-CoV-2 polymerase chain reaction (PCR) test results and 836 of their close contacts. We attempted virus isolation in individuals with re-positive SARS-CoV-2 PCR test results using cell culture and confirmed the presence of neutralizing antibodies using serological tests. Viral culture was negative in all 108 individuals with re-positive SARS-CoV-2 PCR test results in whom viral culture was performed. Three new cases of SARS-CoV-2 infection were identified among household contacts using PCR. Two of the three new cases had had contact with the index patient during their primary illness, and all three had antibody evidence of past infection. Thus, there was no laboratory evidence of viral shedding and no epidemiological evidence of transmission among individuals with re-positive SARS-CoV-2 PCR test results. [ABSTRACT FROM AUTHOR]

Increased awareness of adverse events following immunization (AEFI) can disrupt vaccination programs. In South Korea, a report of alleged influenza vaccine-related deaths attracted significant media attention in 2020. We retrieved the vaccination coverage and AEFI data to determine their association with media coverage. Between 2015 and 2019, the vaccination coverage rate ranged between 80.5% and 83.3%; however, the vaccination coverage rate declined significantly from 2020 to 2021 to 73.6% (p < 0.0001). During the 43rd week of 2020, following a large amount of media coverage on vaccine safety issues, the number of cases with AEFI reached 60. Between 2015 and 2020, the mortality rate ratios for influenza vaccines and non-vaccines ranged between 0.1296 (95% confidence interval (CI), 0.1262–0.1331, p < 0.0001) and 0.1608 (95% CI, 0.1572–0.1644, p < 0.0001). Vaccine safety surveillance should be continued in conjunction with investigation and transparent risk communication to maintain public trust in vaccines and vaccinations. [ABSTRACT FROM AUTHOR]

Vaccine-related errors (VREs) result from mistakes in vaccine preparation, handling, storage, or administration. We aimed to assess physicians' and nurses' experiences of VREs in South Korea, focusing on reconstitution issues, and to understand the barriers to and facilitators of preventing them. This was a cross-sectional study using an internet-based survey to examine experiences of reconstitution-related errors, and experience or preference with regard to ready-to-use vaccines (RTU) by physicians and nurses. A total of 700 participants, including 250 physicians and 450 nurses, responded to the questionnaire. In total, 76.4% and 41.5% of the physicians and nurses, respectively, reported an error related to reconstituted vaccines. All errors had been reported as experienced by between 4.9% and 52.0% of physicians or nurses. The errors were reported to occur in more than one in 100 vaccinations for inadequate shaking of vaccines by 28.0% of physicians and 6.9% of nurses, incomplete aspiration of reconstitution vials by 28.0% of physicians and 6.4% of nurses, and spillage or leakage during reconstitution by 20.8% of physicians and 6.9% of nurses. A total of 94.8% of physicians had experience with RTU vaccines, and all preferred RTU formulations. In conclusion, this study highlights the high frequency and types of reconstitution-related errors in South Korea. RTU vaccines could help reduce the time needed for preparation and reduce the risk of errors in South Korea. [ABSTRACT FROM AUTHOR]

Amid the COVID-19 pandemic, vaccination coverage may decline due to limited accessibility to healthcare. We assessed the impact of the COVID-19 pandemic on vaccination coverage and the incidence of vaccine-preventable diseases (VPDs) in the Republic of Korea. National vaccination coverage of 10 essential vaccines administered to children between January–June 2019 and January–June 2020 was analyzed. The national incidence of selected VPDs was compared for the corresponding periods. During the COVID-19 outbreak, the vaccination rate in children aged 0–35 months in Korea did not decrease significantly, whereas the vaccination rate for children aged 4–6 years decreased by 1.4–1.9%. The overall incidence of VPDs decreased by 10–50% between 2019 and 2020, especially with varicella. Thus, the COVID-19 pandemic did not result in a decrease in vaccination coverage among Korean children, which prevented a surge in VPD incidence. Maintaining essential vaccination coverage without interruption is important during the response to the COVID-19 pandemic. [ABSTRACT FROM AUTHOR]

Introduction: Diverse algorithms for signal detection exist. However, inconsistent results are often encountered among the algorithms due to different levels of specificity used in defining the adverse events (AEs) and signal threshold. We aimed to explore potential safety signals for two pneumococcal vaccines in a spontaneous reporting database and compare the results and performances among the algorithms. Methods: Safety surveillance was conducted using the Korea national spontaneous reporting database from 1988 to 2017. Safety signals for pneumococcal vaccine and its subtypes were detected using the following the algorithms: disproportionality methods comprising of proportional reporting ratio (PRR), reporting odds ratio (ROR), and information component (IC); empirical Bayes geometric mean (EBGM); and tree-based scan statistics (TSS). Moreover, the performances of these algorithms were measured by comparing detected signals with the known AEs or pneumococcal vaccines (reference standard). Results: Among 10,380 vaccine-related AEs, 1135 reports and 101 AE terms were reported following pneumococcal vaccine. IC generated the most safety signals for pneumococcal vaccine (40/101), followed by PRR and ROR (19/101 each), TSS (15/101), and EBGM (1/101). Similar results were observed for its subtypes. Cellulitis was the only AE detected by all algorithms for pneumococcal vaccine. TSS showed the best balance in the performance: the highest in accuracy, negative predictive value, and area under the curve (70.3%, 67.4%, and 64.2%). Conclusion: Discrepancy in the number of detected signals was observed between algorithms. EBGM and TSS calibrated noise better than disproportionality methods, and TSS showed balanced performance. Nonetheless, these results should be interpreted with caution due to a lack of a gold standard for signal detection. [ABSTRACT FROM AUTHOR]

• From 2001 to 2018, the average annual percent change (net drift) of HBsAg positivity was −5.9% (95% confidence interval (CI): −6.9%, −4.8%). • Proportion of women with anti-HBs positivity increased from 59.9% in 2001 to 75.8% in 2018 (P = 0.002). • We observed a concurrent decrease in HBsAg seropositivity and an increase in anti-HBs seropositivity among Korean women of childbearing age. We estimated the impact of universal hepatitis B immunization using 18-year data of women who are of childbearing age in South Korea. We used hepatitis B surface antigen (HBsAg) and antibody (anti-HBs) data of 145,993 women aged 20–49 years during 2001–2018 at the Gangnam CHA Medical Center. Annual prevalences of HBsAg and anti-HBs positivity were calculated and tested for linear trend. We conducted age-period-cohort (APC) analysis to obtain period and cohort effect. Overall proportion of HBsAg positivity was 3.5% (n = 5050) and anti-HBs positivity was 75.3% (n = 109,907) during the study period. HBsAg positivity percentage decreased from 5.1% in 2001 to 2.5% in 2018 (P < 0.001) while anti-HBs positivity increased from 59.9% to 75.8% (P = 0.002). Average annual percent change of HBsAg positivity was −5.9% (95% confidence interval (CI): −6.9%, −4.8%). The period and cohort RR curve identified a consistent decrease in HBsAg positivity over time and across generations. We observed a concurrent decrease in HBsAg and an increase in anti-HBs seropositivity among Korean women of childbearing age, implicating success in preventing vertical transmission. [ABSTRACT FROM AUTHOR]

With the advent of live-attenuated, quadrivalent, and cell-cultured vaccines for influenza, there have been discussions on the safety of these vaccines compared to conventional vaccines (such as inactivated, trivalent, and egg-cultured vaccines) because of the development of neurological adverse events (AEs). This study aimed to compare the trends and safety signals in the AE reporting systems of the US and South Korea and, more particularly, to evaluate the association between influenza vaccination and Guillain–Barré syndrome (GBS). In total, 400,535 AE reports from the US Vaccine Adverse Event Reporting System (VAERS) and 28,766 AE reports from the Korea Adverse Event Reporting System (KAERS) between 2005 and 2017 were assessed. Disproportionality analysis was performed to detect the safety signals and examine the potential risk of GBS with influenza vaccination using the case/non-case approach. In both databases, GBS was the most frequently reported AE following influenza immunization. Using the case/non-case approach, the adjusted reporting odds ratio (ROR) of GBS was 3.57 (95% confidence interval [CI], 3.16–4.03) and 3.09 (95% CI, 0.83–11.45) in the VAERS and KAERS data, respectively. People vaccinated with live-attenuated vaccines reported 2.30 times (95% CI, 1.74–3.05) more cases of GBS than those vaccinated with other types of vaccines. Our analysis of the VAERS and KAERS reports for AEs following immunization (AEFI) for influenza shows the need for cautious monitoring regarding the development of GBS after influenza vaccination, particularly, after live-attenuated vaccination. However, owing to potential reporting bias caused by limited AEFI reports after the introduction of new types of influenza vaccines, further prospective safety studies are needed. [ABSTRACT FROM AUTHOR]

South Korea experienced a low prevalence of SARS-CoV-2 until the emergence of the omicron in early 2022, triggering a major community epidemic. To evaluate effectiveness of NVX-CoV2373 and BNT162b2 vaccines in Korean population, we conducted an observational study utilizing individual-level case data on laboratory-confirmed SARS-CoV-2 infection, along with vaccination record. A total of 47,078 recipients of NVX-CoV2373 vaccine and 7,561 recipients of BNT162b2 vaccine were eligible for the study. Thirty days post-second doses, COVID-19 rates were 7.9% (595 out of 7561) of NVX-CoV2373 recipients and 8.6 % (647 out of 7561) of BNT162b2 recipients experienced COVID-19. NVX-CoV2373 rates increased to 9.8 % and 11.2 % at 60 and 90 days, while BNT162b2 rates were 10.5 % and 11.3 % at the same intervals. The 22-weeks risk ratios for recipients of the NVX-CoV2373 vaccine as compared with recipients of the BNT162b2 vaccine were 1.11 (95 % CI, 0.99 to 1.25) for laboratory-confirmed SARS-CoV-2 infection. Continued monitoring is essential to evaluate the duration of protection across different vaccine platforms and schedules. [ABSTRACT FROM AUTHOR]

Summary: Background: Although there has been substantial progress in controlling pertussis in South Korea, the reported number of pertussis case-patients has gradually been increasing during the last decade. To address this, we summarized the surveillance data on pertussis collected during the period 1955–2011. Detailed epidemiologic and clinical data were determined, primarily using data from recent years. Methods: We analyzed data from the national surveillance system to describe the occurrence of pertussis. The annual numbers of reported pertussis case-patients were identified for the period 1955–2000. For 2001–2009, information including limited demographic characteristics and the date of onset of symptoms were identified. For 2010–2011, detailed epidemiologic and clinical information of reported pertussis case-patients were collected. Results: During 1955–2011, the secular trend was characterized by a gradual decrease in the reported number of cases from 1955 to the late 1990s, then a recent increase starting in the early 2000s. In 2009, a large number of reported cases occurred in infants <1 year of age. In 2011, an increase in reported cases among adolescents and adults aged ≥15 years was observed. During 2010–2011, 29.8% of reported cases were not immunized and 11.3% had not been immunized in a timely manner. Of adolescents and adults aged ≥15 years, 91.7% did not have a record of immunization. Conclusions: During 2010–2011, a shift in age group was observed in pertussis case-patients: 33.8% were young infants <3 months of age and 29.0% were adolescents and adults ≥15 years of age. Considering that infants without timely vaccination may be vulnerable to an increased risk of pertussis infection, steps to provide timely vaccination to infants, to provide Tdap vaccination to adolescents and adults, and to enhance surveillance to capture adult pertussis cases should be taken in South Korea. [Copyright &y& Elsevier]

Summary: Background: Japanese encephalitis (JE) was the leading cause of viral encephalitis among children in South Korea in the 20th century. This study summarizes recent changes in the epidemiology of JE following the implementation of a vigorous immunization program in the country. Methods: Epidemiological investigations were performed for all reported laboratory-confirmed JE cases, and the cumulative incidence was calculated for the surveillance years 2007–2010. Results: During the surveillance period, 45 cases of JE were confirmed in the country, resulting in a cumulative incidence of 0.013–0.055 cases per 100 000 population. The median age of cases was 49.4 years, and by age group, 44.4% were aged 40–49 years. Just under a quarter (22.2%) of the cases were found to live close to a pigsty, while 42.2% of the cases were found to reside in the metropolitan areas of Seoul, Incheon, and Gyeonggi-do. None of the cases had a history of vaccination. Conclusions: Although JE has traditionally been regarded as a children''s disease, the majority of cases now occur in adults in countries where strong immunization programs exist, such as in South Korea. Consideration should be given to an adult vaccination policy in the near future. [Copyright &y& Elsevier]

• Our results suggest moderate protection (53.4%) of IIV3 against RT-PCR laboratory-confirmed influenza in children in the 2017–2018 influenza season. • Vaccine effectiveness using RIDT was lower than RT-PCR. • Vaccine effectiveness against influenza A was higher than influenza B. • Vaccine effectiveness against all influenza was higher in older age group. In Korea, the National Immunization Program provided trivalent inactivated influenza vaccines (IIV3) to all children aged 6–59 months during the 2017–2018 season. In this study, we aimed to evaluate the vaccine effectiveness (VE) of IIV3 in children during the 2017–2018 season. Children aged 6–59 months who were tested for influenza for their acute respiratory illness in four hospitals during the 2017–2018 influenza season were included. We estimated the VE of IIV3 by test-negative case-control design based on the rapid influenza diagnostic test (RIDT) or reverse transcription polymerase chain reaction (RT-PCR) test results. A total of 4738 children were included in this study. The number of laboratory-confirmed influenza cases was 845 (17.8%), and there were 478 cases of influenza A and 362 cases of influenza B. The adjusted VE based on RT-PCR was 53.4% (95% CI, 25.3–70.5) against any influenza, 68.8% (95% CI, 38.7–84.1) against influenza A, and 29.7% (95% CI, −35.1 to 61.8) for influenza B. The adjusted VE based on RIDT was 14.8% (95% CI, −4.4 to 30.0) against any influenza, 24.2% (95% CI, 3.1–40.2) against influenza A, and −5.1% (95% CI, −42.6 to 21.4) against influenza B. Age-specific VE based on RT-PCR against any influenza was 44.1% (95% CI, −0.2 to 67.8) in children aged 6 months to 2 years and 59.3% (95% CI, 8.8–81.9) in children aged 3–<5 years. Our results suggest moderate protection (53.4%) of IIV3 against RT-PCR laboratory-confirmed influenza in children in the 2017–2018 influenza season. However, the RIDT hampered the validity to assess VE during influenza season. Caution is needed when interpreting an RIDT-based test negative design influenza VE study. [ABSTRACT FROM AUTHOR]