Preparing for the next respiratory pathogen pandemic: using tabletop simulation exercises to strengthen national planning in Cook Islands, Costa Rica, Lebanon and Mongolia.

The Preparedness and Resilience for Emerging Threats (PRET) initiative takes an innovative mode-of-transmission approach to pandemic planning by advocating for integrated preparedness and response systems and capacities for groups of pathogens with common transmission pathways. The World Health Organization (WHO) launched this initiative in 2023 with the publication of PRET Module 1 addressing respiratory pathogens. Exercise PanPRET-1 is a customizable tabletop simulation exercise (TTX) package developed to complement PRET Module 1. The exercise scenario focuses on strengthening capacities for multisectoral coordination, risk communication and community engagement, and the triggers for operational decision-making. This article reports on the experiences of the first four countries to implement Exercise PanPRET-1: Cook Islands, Costa Rica, Lebanon and Mongolia. Exercise outcomes demonstrated that PanPRET-1 can be an effective tool for testing pandemic plans in a multisectoral forum and identifying opportunities to improve preparedness and response in key domains. In quantitative evaluations in Cook Islands, Costa Rica and Mongolia, high proportions of exercise participants indicated that multiple aspects of the exercise were well-designed and were beneficial for improving health emergency preparedness. Exercise participants in Lebanon provided qualitative feedback indicating that they found the exercise to be beneficial. Conducting a TTX and monitoring the implementation of action plans based on exercise findings facilitates a country-owned whole-of-society vision for pandemic planning. Countries are encouraged to incorporate TTX such as Exercise PanPRET-1 into a continuous cycle of activity to improve pandemic preparedness.

Effect of pneumococcal conjugate vaccine six years post-introduction on pneumococcal carriage in Ulaanbaatar, Mongolia.

Limited data from Asia are available on long-term effects of pneumococcal conjugate vaccine introduction on pneumococcal carriage. Here we assess the impact of 13-valent pneumococcal conjugate vaccine (PCV13) introduction on nasopharyngeal pneumococcal carriage prevalence, density and antimicrobial resistance. Cross-sectional carriage surveys were conducted pre-PCV13 (2015) and post-PCV13 introduction (2017 and 2022). Pneumococci were detected and quantified by real-time PCR from nasopharyngeal swabs. DNA microarray was used for molecular serotyping and to infer genetic lineage (Global Pneumococcal Sequence Cluster). The study included 1461 infants (5-8 weeks old) and 1489 toddlers (12-23 months old) enrolled from family health clinics. We show a reduction in PCV13 serotype carriage (with non-PCV13 serotype replacement) and a reduction in the proportion of samples containing resistance genes in toddlers six years post-PCV13 introduction. We observed an increase in pneumococcal nasopharyngeal density. Serotype 15 A, the most prevalent non-vaccine-serotype in 2022, was comprised predominantly of GPSC904;9. Reductions in PCV13 serotype carriage will likely result in pneumococcal disease reduction. It is important for ongoing surveillance to monitor serotype changes to potentially inform new vaccine development.

Incidence and Mortality due to Colorectal Cancer in Mongolia, 2018-2022.

OBJECTIVE: We aimed to update data on the morbidity and mortality rate of colorectal cancer (CRC) among the population of Mongolia by province between 2018 and 2022. METHODS: This study was designed using a descriptive method. The data were collected from 21 general hospitals of provinces, 9 general hospitals of districts, and the National Cancer Center in 2018-2022. The incidence and mortality were calculated as mean annual numbers per 100,000 populations. The age-standardized rate (ASR) was utilized by the direct method, and it was rated by weighted average of age-specific incidence rates against the world population. RESULT: In the country, a total of 1316 new cases were diagnosed and 782 deaths were caused by CRC in the last 5 years (2018-2022). The incidence of CRC in the last 5 years (2018-2022) was 7.9 per 100,000 populations, and the mortality rate was 4.7 per 100,000. The provinces of Orkhon (12), Khentii (11), and Central (10) reported the highest incidences of CRC, whereas the provinces of Sukhbaatar (6.9), Selenge (6.6), Dornod (6), and Darkhan-Uul (6) had the highest death rates (per 100,000 populations). The incidence of CRC didn't differ statistically significantly between men and women. Additionally, the estimated incidence has grown dramatically with patients' ages. CONCLUSION: Our study presents evidence of a steadily increasing CRC incidence in Mongolia over the past five years. Therefore, it is necessary to determine the distribution of risk factors, learn from.

Core health system measures response to COVID-19 among East Asian countries.

Objective: The purpose of this study is to summarize the health system response to COVID-19 in four East Asian countries, analyze the effectiveness of their health system response, and provide lessons for other countries to control the epidemic and optimize their health system response. Methods: This study investigated and summarized COVID-19 data and health system response in four East Asian countries, China, Japan, Mongolia, and South Korea from national governments and ministries of health, WHO country offices, and official websites of international organizations, to assess the effectiveness of health system measures. Result: As of June 30, 2022, all four countries are in a declining portion of COVID-19. China has two waves, and new cases increased slowly, with the total cases per million remaining within 4, indicating a low level. Japan has experienced six waves, with case growth at an all-time high, total cases per million of 250.994. Mongolia started the epidemic later, but also experienced four waves, with total cases per million of 632.658, the highest of the four countries. South Korea has seen an increasing number of new cases per wave, with a total case per million of 473.759. Conclusion: In containment strategies adopted by China and Mongolia, and mitigation strategies adopted by Japan and South Korea, health systems have played important roles in COVID-19 prevention and control. While promoting vaccination, countries should pay attention to non-pharmaceutical health system measures, as evidenced by: focusing on public information campaigns to lead public minds; strengthening detection capabilities for early detection and identification; using technical ways to participate in contact tracing, and promoting precise judging isolation.

Acceptance of Self-Sampling and Knowledge about Human Papillomavirus among Women in Mongolia.

BACKGROUND: Mongolia faces a significant burden of cervical cancer, with the highest prevalence of Human Papillomavirus (HPV) in the region. Cervical cancer ranks as the third most common cancer among women in the country. This study aimed to assess the acceptance of self-sampling among young women in Mongolia and evaluate their knowledge regarding HPV and cervical cancer. METHODS: In this study, participants provided a self-administered vaginal swabs to detect high-risk HPV genotypes. Both acceptability of self-sampling using swabs and participants knowledge regarding HPV and cervical cancer through a scored questionnaire were assessed.  The knowledge scale was categorized into three groups: low (0-2), moderate (3-4) and high (5-6). RESULTS: A total of 203 women aged 24-28 years completed the questionnaire and provided self-administered vaginal swabs. The majority (95.1%) found self-sampling technique using Copan Self Vaginal FLOQSwabs® easy to perform. Additionally, 98.5% indicated that the self-swab instructions were clear and comprehensive, while 94.1% reported no pain during the process. Furthermore, 67.8% of participants expressed a preference for performing the swab in a clinic rather than at home. All respondents chose self-sampling due to greater personal privacy, tranquility, reduced anxiety and time optimization. The questionnaire results revealed an overall low level of knowledge about HPV among participants, with a mean score at 1.9 out of 6 [95%CI 1.67-2.21] and a moderate level of knowledge regarding cervical cancer risks, with a mean score at 3.7 out of 6 [95%CI 3.19-4.21]. This pattern was consistent across both vaccinated and unvaccinated cohorts, indicating a strong demand for enhanced awareness of HPV and cervical cancer. CONCLUSIONS: This study demonstrates the high acceptance of self-sampling among young women aged 24-28 years in Mongolia. However, it also  underscores a significant need for improved awareness initiatives concerning HPV and cervical cancer in Mongolia.

Analysis of the Correlation between FH and PCSK9 and APOB Gene Mutations in Han and Mongolian Populations of the Hulunbuir.

BACKGROUND: The goal of the study was to provide an individual and precise genetic and molecular biological basis for the early prevention, diagnosis, and treatment of local FH by analyzing the risk factors for the development of FH in Han and Mongolian patients in the Hulunbuir, comparing the lipid levels of FH patients of the two ethnicities, and assessing differences in mutations to two genes between the two ethnic groups. METHODS: Twenty cases each of Han Chinese and Mongolian healthy controls and fifty patients who each met the inclusion criteria from November 2021 to December 2022 in five general hospitals in Hulunbuir were selected. Multifactor logistic analysis was used to analyze the risk factors associated with the development of FH. We used t-tests to analyze statistical differences in lipid levels between the groups, and Sanger sequencing to detect the dis-tribution of common mutation sites of PCSK9 and APOB in all study subjects. The mutation rates and differences between regions and ethnic groups were summarized and compared. RESULTS: 1) Gender, age, alcohol consumption, dietary status, and a family history of FH were risk factors associated with the development of FH. 2) TC, LDL-C, and APOB were significantly higher in Mongolian cases than Han cases (p < 0.05). sdLDL-C was not statistically different between the two ethnicities (p > 0.05). 3) We detected four (8%) heterozygous mutations at the PCSK9 gene E670G mutation site in the Han case group and a total of nine (18%) mutations at this site in the Mongolian cases, including one (2%) homozygous and eight (16%) heterozygous mutations. One case of a heterozygous mutation was detected in the Mongolian control group. We detected a total of ten (20%) mutations at the APOB gene rs1367117 mutation site in the Han case group, including eight (16%) heterozygous and two (4%) homozygous mutations, 11 cases (22%) of heterozygous mutations in the Mongolian case group, two cases of heterozygous mutations in the Han control group, and one case of a heterozygous mutation in the Mongolian control group. 4) The D374Y and S127R mutation sites of PCSK9 and the R3500Q mutation site of APOB were not detected in any of the study subjects. CONCLUSIONS: The mutation sites of the PCSK9 and APOB genes in FH patients in Hulunbuir are different from other regions, and the mutation rate is higher than in other regions. Therefore, we recommend that the mutation sites of the PCSK9 and APOB genes described herein be used as clinical detection indicators to assist the diagnosis of FH in this region.

Respiratory Syncytial Virus and Influenza Infections in Children in Ulaanbaatar, Mongolia, 2015-2021.

BACKGROUND: Data available for RSV and influenza infections among children < 2 years in Mongolia are limited. We present data from four districts of Ulaanbaatar from April 2015 to June 2021. METHODS: This study was nested in an enhanced surveillance project evaluating pneumococcal conjugate vaccine (PCV13) impact on the incidence of hospitalized lower respiratory tract infections (LRTIs). Our study was restricted to children aged < 2 years with arterial O2 saturation < 93% and children with radiological pneumonia. Nasopharyngeal (NP) swabs collected at admission were tested for RSV and influenza using qRT-PCR. NP swabs of all patients with radiological pneumonia and of a subset of randomly selected NP swabs were tested for S. pneumoniae (S.p.) by qPCR and for serotypes by culture and DNA microarray. RESULTS: Among 5705 patients, 2113 (37.0%) and 386 (6.8%) had RSV and influenza infections, respectively. Children aged 2-6 months had a higher percentage of very severe RSV infection compared to those older than 6 months (42.2% versus 31.4%, p-value Fisher's exact = 0.001). S.p. carriage was detected in 1073/2281 (47.0%) patients. Among S.p. carriage cases, 363/1073 (33.8%) had S.p. and RSV codetection, and 82/1073 (7.6%) had S.p. and influenza codetection. S.p. codetection with RSV/influenza was not associated with more severe LRTIs, compared to only RSV/influenza cases. CONCLUSION: In Mongolia, RSV is an important pathogen causing more severe LRTI in children under 6 months of age. Codetection of RSV or influenza virus and S.p. was not associated with increased severity.

Factors associated with recurrence in patients with oral cancer in Mongolia.

INTRODUCTION: In Mongolia, there has been limited research on the posttreatment survival rate, recurrence, and occurrence of oral cancer. The goal of this study is to investigate the risk factors that contribute to the recurrence of oral cancer to increase survival rates, facilitate early detection, and improve treatment accuracy. METHOD: A retrospective cohort method was used, with medical records from 173 patients diagnosed with squamous cell carcinoma of the mouth at the National Cancer Center of Mongolia's Department of Head and Neck Surgery, Radio, and Chemotherapy between 2012 and 2017. The Mongolian National University of Medical Sciences' Research Ethics Committee approved the project. RESULTS: The findings revealed that 109 cases (63.0%) were men and 64 (37.0%) were females, with a large proportion of patients (28.3%) falling between the ages of 61 and 70. Men had a 3.8 times higher risk of cancer recurrence than women (OR = 3.79, CI = 1.24-11.57). Furthermore, lymph node metastases and treatment were linked to oral cancer recurrence. CONCLUSION: This study offers light on the factors that influence the recurrence of oral cancer, giving useful insights for improving patient outcomes through early detection and proper treatment.

Delays in health seeking, diagnosis and treatment for tuberculosis patients in Mongolia: an analysis of surveillance data, 2018-2021.

Early diagnosis and treatment of infectious tuberculosis (TB) is essential to the attainment of global targets specified in the End TB Strategy. Using case-based TB surveillance data, we analysed delays in health seeking, diagnosis and treatment among TB patients in Mongolia from 2018 to 2021. We calculated the median and interquartile range (IQR) for "diagnostic delay," defined as the time from symptom onset to diagnosis, subdivided into "health-seeking delay" (time from symptom onset to first visit to a health facility) and "health facility diagnostic delay" (time from first health facility visit to diagnosis), and for "treatment delay," defined as the time from diagnosis to start of treatment. We also calculated "total delay," defined as the time from symptom onset to treatment start. Based on data for 13 968 registered TB patients, the median total delay was estimated to be 37 days (IQR, 19-76). This was mostly due to health-seeking delay (median, 23 days; IQR, 8-53); in contrast, health facility diagnostic delay and treatment delay were relatively short (median, 1 day; IQR, 0-7; median, 1 day; IQR, 0-7, respectively). In 2021, health-seeking delay did not differ significantly between men and women but was shorter in children than in adults and shorter in clinically diagnosed than in bacteriologically confirmed TB cases. Health-seeking delay was longest in the East region (median, 44.5 days; IQR, 20-87) and shortest in Ulaanbaatar (median, 9; IQR, 14-64). TB treatment delay was similar across sexes, age groups and types of TB diagnosis but slightly longer among retreated cases and people living in Ulaanbaatar. Efforts to reduce TB transmission in Mongolia should prioritize decreasing delays in health seeking.

Phylogenetic analysis of small ruminant lentiviruses in Mongolian sheep supports an ancient east-west split for the genotype A.

The ovine maedi-visna virus (MVV) and caprine arthritis-encephalitis virus (CAEV) are small ruminant lentiviruses (SRLVs) with striking genetic and structural similarities. The presence of SRLV in Mongolian sheep and goats was serologically demonstrated more than a decade ago; however, the viral genotype remains unknown. In total, 329 blood samples were collected from two sheep breeds (i.e., Khalkha and Sumber) in Tov, Govisumber, Arkhangay, Dornogovi, Zavkhan, and Sukhbaatar provinces, Mongolia. Serological and phylogenetic analyses were performed regardless of any apparent clinical signs, although most of the animals appeared healthy. All sheep in three of the six provinces were seronegative, whereas the seroprevalence in the Tov, Govisumber, and Zavkhan provinces averaged 7.9%. Genomic DNA from seropositive animals was tested using hemi-nested polymerase chain reaction, and sub-genomic SRLV sequences were determined from nine samples. Mongolian SRLV sequences clustered within the divergent subtype A22, which was previously found only in Fertile Crescent regions, including Lebanon, Jordan, and Iran, where the first sheep-domestication (Ovis aries) occurred. According to the phylogenetic analysis, genotype A has two ancestors from the ancient Fertile Crescent: (1) Turkish strains and (2) Iranian, Jordanian, and Lebanese strains. The first ancestor spread westward, whereas the second spread eastward, ultimately reaching Mongolia.

Effect of Pneumococcal Conjugate Vaccine on Pneumonia Incidence Rates among Children 2-59 Months of Age, Mongolia, 2015-2021.

Starting in June 2016, the 13-valent pneumococcal conjugate vaccine (PCV13) was introduced into the routine immunization program of Mongolia by using a 2+1 dosing schedule, phased by district. We used prospective hospital surveillance to evaluate the vaccine's effect on pneumonia incidence rates among children 2-59 months of age over a 6-year period. Of 17,607 children with pneumonia, overall adjusted incidence rate ratios showed decreased primary endpoint pneumonia, very severe pneumonia, and probable pneumococcal pneumonia until June 2021. Results excluding and including the COVID-19 pandemic period were similar. Pneumonia declined in 3 districts that introduced PCV13 with catch-up campaigns but not in the 1 district that did not. After PCV13 introduction, vaccine-type pneumococcal carriage prevalence decreased by 44% and nonvaccine-type carriage increased by 49%. After PCV13 introduction in Mongolia, the incidence of more specific pneumonia endpoints declined in children 2-59 months of age; additional benefits were conferred by catch-up campaigns.

Strengthening national salt reduction strategies using multiple methods process evaluations: case studies from Malaysia and Mongolia.

OBJECTIVE: To understand the extent to which national salt reduction strategies in Malaysia and Mongolia were implemented and achieving their intended outcomes. DESIGN: Multiple methods process evaluations conducted at the mid-point of strategy implementation, guided by theoretical frameworks. SETTING: Malaysia (2018-2019) and Mongolia (2020-2021). PARTICIPANTS: Desk-based reviews of related documents, interviews with key stakeholders (n 12 Malaysia, n 10 Mongolia), focus group discussions with health professionals in Malaysia (n 43) and health provider surveys in Mongolia (n 12). RESULTS: Both countries generated high-quality local evidence about salt intake and levels in foods and culturally specific education resources. In Malaysia, education and reformulation activities were delivered with moderate dose (quantity) but reach among the population was low. Within 5 years, Mongolia implemented education among schools, health professionals and food producers on salt reduction with high reach, but with moderate dose (quantity) and reach among the general population. Both countries faced challenges in implementing legislative interventions (mandatory salt labelling and salt limits in packaged foods) and both could improve the scaling up of their reformulation and education activities. CONCLUSIONS: In the first half of Malaysia's and Mongolia's strategies, both countries generated necessary evidence and education materials, mobilised health professionals to deliver salt reduction education and achieved small-scale reformulation in foods. Both subsequently should focus on implementing regulatory policies and achieving population-wide reach and impact. Process evaluations of existing salt reduction strategies can help strengthen intervention delivery, aiding achievement of WHO's 30 % reduction in salt intake by 2025 target.

Questionnaire survey on public awareness of cleft lip with/without palate in Mongolia.

The frequency of cleft lip with/without palate (CL/P) in the Mongolian population is approximately 1 in 1314 live births. This research aims to disseminate information about this congenital disability to the public to better understand CL/P, and people's fissures, and review administrative measures, as there is a lack of research in this area. A questionnaire survey was conducted using Google Forms, with 1000 Mongolian participants. Most participants (86.7%) said they had knowledge of the word, whereas 86.2% said they had knowledge of the condition. Most participants' answers were question-related disadvantages of CL/P patients, including statements such as "It's uncomfortable in human relationships" and "It makes an uncomfortable impression on the person you meet the first time." The results of this study revealed that most Mongolians were aware of CL/P and are concerned about patients. However, the causes of CL/P in the general population remain unknown, and further research is needed in this area.

Risk factors associated with hepatitis D virus infection and preventive strategies in Mongolia.

BACKGROUND: Hepatitis D virus (HDV) infection is highly prevalent in Mongolia. We aimed to identify the risk factors associated with HDV infection, propose preventive strategies, and evaluate the outcomes of a 3-year collaborative project between Taiwan and Mongolia. METHODS: In 2016 and 2018, we conducted onsite visits to Mongolia. Mongolian investigators collected questionnaires focusing on risk factors, demographic characteristics, and serum samples for acute HDV infections. Furthermore, 19 Mongolian seed teachers participated in a 1-week workshop on infection control in Taiwan. Subsequently, these seed teachers trained more than 400 medical personnel in Mongolia. To assess secular changes in acute HDV infection, we reviewed the registration data from the National Center for Communicable Disease (NCCD) in Mongolia between 2011 and 2021. RESULTS: Among the 194 Mongolian patients, 108 had dual infection with hepatitis B virus (HBV) and HDV, while 86 had acute hepatitis B (AHB). Patients with HBV/HDV dual infections were older (28.6 vs 25.5 years, p = 0.030) and had lower rates of positive hepatitis B e antigen in their sera, lower rates of serum HBV DNA exceeding 2000 IU/mL, and higher rates of having received dental treatment (59.4% vs 40.5%, p = 0.014) and injection therapy (64.2% vs 44.0%, p = 0.009) compared with those with AHB. Analysis of NCCD data revealed that new HDV infection cases were more prevalent between 2011 and 2015 (111.20 ± 29.79 cases/y) and decreased to 54.67 ± 27.34 cases/y between 2016 and 2021 ( p = 0.010). CONCLUSION: Dental treatment and injections were associated with a higher risk of acute HDV infections in Mongolia. Through collaborative efforts, the incidence rate of HDV infection has declined in recent years.

Assessing the contributions of an urban population health initiative to shift political priority towards cardiovascular health: three case studies from Brazil, Mongolia and Senegal.

BACKGROUND: The urban population health initiative was designed as a multidisciplinary, multisector programme to address cardiovascular (CV) disease, specifically hypertension and its underlying causes in the cities of Ulaanbaatar, Mongolia; Dakar, Senegal; and São Paulo, Brazil. This article aims to provide an overview of the history and dynamics of CV disease policy making in the three countries, to present the policy reform contributions of the initiative and its role in the policy agenda-setting framework/process in each country and to identify the enablers and challenges to the initiative for doing so. METHODS: A qualitative case study was conducted for each setting from November 2020 to January 2021, comprised of a document review, semi-structured in-depth interviews and unstructured interviews with stakeholders involved in the initiative. The literature review included documents from the initiative and the peer-reviewed and grey literature with a total of 188 documents screened. Interviews were conducted with 21 stakeholders. Data collection and thematic analysis was guided by (i) the Kingdon multiple streams conceptual framework with the main themes being CV disease problems, policy, politics and the role of policy entrepreneurs; and (ii) the study question inquiring on the role of the urban population health initiative at the CV disease policy level and enabling and challenging factors to advancing CV disease policy. Data were thematically analysed using the Framework Method. RESULTS: Each setting was characterized by a high hypertension and CV disease burden combined with an aware and proactive political environment. Policy outcomes attributed to the initiative were updating the guidelines and/or algorithms of care for hypertension and including revised physical and nutritional education in school curricula, in each city. Overall, the urban health initiative's effects in the policy arena, were most prominent in Mongolia and Senegal, where the team effectively acted as policy entrepreneur, promoting the solutions/policies in alignment with the most pressing local problems and in strong involvement with the political actors. The initiative was also involved in improving access to CV disease drugs at primary health levels. Its success was influenced by the local governance structures, the proximity of the initiative to the policy makers and the local needs. In Brazil, needs were expressed predominantly in the clinical practice. CONCLUSIONS: This multi-country experience shows that, although the policy and political environment plays its role in shaping initiatives, often the local priority needs are the driving force behind wider change.

SARS-CoV-2 Infection in Beaver Farm, Mongolia, 2021.

We report an outbreak of COVID-19 in a beaver farm in Mongolia in 2021. Genomic characterization revealed a unique combination of mutations in the SARS-CoV-2 of the infected beavers. Based on these findings, increased surveillance of farmed beavers should be encouraged.

Anxiety, depression, and brain overwork in the general population of Mongolia.

In Mongolia, there is limited data on the prevalence and correlates of common mental health conditions. This study addresses this data gap by exploring anxiety, depression, and brain overwork. The aim of this study was to determine normative data on these conditions in the general population of Mongolia. This nationwide, population-based, cross-sectional study was conducted in 48 sampling centers across Mongolia in 2020. A total of 613 participants (190 men and 423 women) with a mean age of 41.8 ± 12.4 years were recruited. The participants completed the Hospital Anxiety and Depression Scale (HADS) and the Brain Overwork Scale (BOS-10). Vital signs, body measurements, and lifestyle determinants were also assessed. The prevalence of anxiety was 9.9%, depression was 4.9%, and brain overwork was 18.3% among the participants. Anxiety and depression were correlated with brain overwork symptoms. Brain overwork was associated with young age, unemployment, low income, and alcohol use. These findings suggest that anxiety, depression, and brain overwork are a significant problem in the general population of Mongolia. Further research is needed to develop effective interventions to reduce the prevalence and risk factors of anxiety, depression, and brain overwork.

Vitamin D supplements for fracture prevention in schoolchildren in Mongolia: analysis of secondary outcomes from a multicentre, double-blind, randomised, placebo-controlled trial.

BACKGROUND: Vitamin D supplementation has been shown to increase total hip areal bone mineral density in healthy children and adolescents. We aimed to investigate whether supplementing schoolchildren living in Mongolia with weekly vitamin D3 for 3 years affected fracture risk. METHODS: We did a multicentre, double-blind, randomised, placebo-controlled trial across 18 public schools in Ulaanbaatar, Mongolia. Schoolchildren were eligible if they were aged 6-13 years at screening, had a negative QuantiFERON-TB Gold In-tube assay (QFT) result, were not hypersensitive to vitamin D or immunocompromised, did not use vitamin D supplements, did not have clinical signs of rickets, and had no intention of leaving Ulaanbaatar within 3 years. Participants were randomly assigned (1:1) to receive either vitamin D (oral dose of 14 000 international units [IU] vitamin D3, once per week) or placebo for 3 years using permuted block randomisation stratified by school of attendance. Participants, care providers, and all trial staff were masked to group assignment during the intervention. Prespecified secondary outcomes were incidence of fractures and adverse events, ascertained using questionnaires. The fracture and safety analyses included participants who completed at least one follow-up fracture questionnaire. We estimated adjusted risk ratios (RRs) and 95% CIs using generalised linear models with binomial distribution and a log link function with adjustment for school of attendance. The trial is registered with ClinicalTrials.gov, NCT02276755, and the intervention ended in May, 2019. FINDINGS: Between Sept 2, 2015, and March 20, 2017, 11 475 children were invited to participate in the study and 8851 were recruited and randomly assigned to receive either vitamin D (n=4418) or placebo (n=4433). 8348 participants were included in the fracture and safety analyses (4176 [94·5%] in the vitamin D group and 4172 [94·1%] in the placebo group). Of these, 4125 (49·4%) were female, 4223 (50·6%) were male, and 7701 (92·2%) were of Khalkh ancestry. Median age was 9·2 years (IQR 8·0-10·7) and 7975 (95·5%) participants had baseline serum 25-hydroxyvitamin D concentrations less than 50 nmol/L. During a median follow-up of 3·0 years (IQR 2·9-3·1), 268 (6·4%) participants in the vitamin D group and 253 (6·1%) in the placebo group reported one or more fractures (adjusted RR 1·10, 95% CI 0·93-1·29; p=0·27). Incidence of adverse events did not differ between study groups. INTERPRETATION: Oral vitamin D supplementation at a dose of 14 000 IU/week for 3 years was safe, but did not influence fracture risk in schoolchildren living in Mongolia who had a high baseline prevalence of vitamin D deficiency. FUNDING: US National Institutes of Health.