Resilience after a nuclear accident: readiness in using mobile phone applications to measure radiation and health indicators in various groups (SHAMISEN SINGS project).

An anonymous web-based survey was developed to check different aspects (SHAMISEN SINGS project): stakeholder awareness and perceptions of available mobile applications (apps) for measuring ionising radiation doses and health/well-being indicators; whether they would be ready to use them in the post-accidental recovery; and what are their preferred methodologies to acquire information etc. The results show that participation of the citizens would be most beneficial during post-accident recovery, providing individual measurements of external ionizing dose and health/well-being parameters, with possible follow-up. Also, participants indicated different preferences for sources to gain knowledge on ionising radiation and for the functions that an ideal app should have. The level of awareness and readiness to use apps to measure ionising radiation dose depended on two main aspects: individual differences (age & gender) and whether people were from countries affected by the previous major accidents. We concluded that stakeholders could have benefits from the data management plan: (1) it potentiates resilience at individual and community level; (2) citizens' measurements contribute to environmental monitoring and public health screening; (3) linkages between different types of data (environmental exposure, individual behavioural diaries, and measurements of health indicators) allow to perform more rigorous epidemiological studies.

Development and external validation of the DOAT and DOATS scores: simple decision support tools to identify disease progression among nonelderly patients with mild/moderate COVID-19.

BACKGROUND: During the fifth wave of the coronavirus disease 2019 (COVID-19) pandemic in Japan, which took place between June and September 2021, a significant number of COVID-19 cases with deterioration occurred in unvaccinated individuals < 65 years old. However, the risk factors for COVID-19 deterioration in this specific population have not yet been determined. This study developed a prediction method to identify COVID-19 patients < 65 years old who are at a high risk of deterioration. METHODS: This retrospective study analyzed data from 1,675 patients < 65 years old who were admitted to acute care institutions in Fukushima with mild-to-moderate-1 COVID-19 based on the Japanese disease severity criteria prior to the fifth wave. For validation, 324 similar patients were enrolled from 3 hospitals in Yamagata. Logistic regression analyses using cluster-robust variance estimation were used to determine predictors of disease deterioration, followed by creation of risk prediction scores. Disease deterioration was defined as the initiation of medication for COVID-19, oxygen inhalation, or mechanical ventilation starting one day or later after admission. RESULTS: The patients whose condition deteriorated (8.6%) tended to be older, male, have histories of smoking, and have high body temperatures, low oxygen saturation values, and comorbidities, such as diabetes/obesity and hypertension. Stepwise variable selection using logistic regression to predict COVID-19 deterioration retained comorbidities of diabetes/obesity (DO), age (A), body temperature (T), and oxygen saturation (S). Two predictive scores were created based on the optimism-corrected regression coefficients: the DOATS score, including all of the above risk factors, and the DOAT score, which was the DOATS score without oxygen saturation. In the original cohort, the areas under the receiver operating characteristic curve (AUROCs) of the DOATS and DOAT scores were 0.81 (95% confidence interval [CI] 0.77-0.85) and 0.80 (95% CI 0.76-0.84), respectively. In the validation cohort, the AUROCs for each score were both 0.76 (95% CI 0.69-0.83), and the calibration slopes were both 0.80. A decision curve analysis confirmed the clinical practicability of both scores in the validation cohort. CONCLUSIONS: We established two prediction scores that can quickly evaluate the risk of COVID-19 deterioration in mild/moderate patients < 65 years old.

Real-world clinical outcomes of treatment with molnupiravir for patients with mild-to-moderate coronavirus disease 2019 during the Omicron variant pandemic.

It is unclear whether molnupiravir has a beneficial effect on vaccinated patients infected with the Omicron variant of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We here evaluated the efficacy of molnupiravir in patients with mild-to-moderate coronavirus disease 2019 (COVID-19) during the Omicron variant surge in Fukushima Prefecture, Japan. We enrolled patients with mild-to-moderate COVID-19 who were admitted to hospitals between January and April, 2022. Clinical deterioration after admission was compared between molnupiravir users (n = 230) and non-users (n = 690) after 1:3 propensity score matching. Additionally, we performed forward stepwise multivariate logistic regression analysis to evaluate the association between clinical deterioration after admission and molnupiravir treatment in the 1:3 propensity score-matched subjects. The characteristics of participants in both groups were balanced as indicated by covariates with a standardized mean difference of < 0.1. Regarding comorbidities, there was no imbalance between the two groups, except for the presence of hypertension, dyslipidemia, diabetes mellitus, and cardiac disease. The clinical deterioration rate was significantly lower in the molnupiravir users compared to the non-users (3.90% vs 8.40%; P = 0.034). Multivariate logistic regression analysis demonstrated that receiving molnupiravir was a factor for preventing deterioration (odds ratio 0.448; 95% confidence interval 0.206-0.973; P = 0.042), independent of other covariates. This real-world study demonstrates that molnupiravir contributes to the prevention of deterioration in COVID-19 patients after hospitalization during the Omicron variant phase.

Real-world clinical outcomes of treatment with casirivimab-imdevimab among patients with mild-to-moderate coronavirus disease 2019 during the Delta variant pandemic.

Background: Mutations of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) may reduce the efficacy of neutralizing monoclonal antibody therapy against coronavirus disease 2019 (COVID-19). We here evaluated the efficacy of casirivimab-imdevimab in patients with mild-to-moderate COVID-19 during the Delta variant surge in Fukushima Prefecture, Japan. Methods: We enrolled 949 patients with mild-to-moderate COVID-19 who were admitted to hospital between July 24, 2021 and September 30, 2021. Clinical deterioration after admission was compared between casirivimab-imdevimab users (n = 314) and non-users (n = 635). Results: The casirivimab-imdevimab users were older (P < 0.0001), had higher body temperature (≥ 38°C) (P < 0.0001) and greater rates of history of cigarette smoking (P = 0.0068), hypertension (P = 0.0004), obesity (P < 0.0001), and dyslipidemia (P < 0.0001) than the non-users. Multivariate logistic regression analysis demonstrated that receiving casirivimab-imdevimab was an independent factor for preventing deterioration (odds ratio 0.448; 95% confidence interval 0.263-0.763; P = 0.0023). Furthermore, in 222 patients who were selected from each group after matching on the propensity score, deterioration was significantly lower among those receiving casirivimab-imdevimab compared to those not receiving casirivimab-imdevimab (7.66% vs 14.0%; p = 0.021). Conclusion: This real-world study demonstrates that casirivimab-imdevimab contributes to the prevention of deterioration in COVID-19 patients after hospitalization during a Delta variant surge.

Development of an Application for Sustainable Support of Returning Residents Displaced by the Fukushima Nuclear Accident.

We developed a mobile application (app) to help communication between support providers and residents who have returned from evacuation after the Fukushima nuclear power plant accident. Surveys were conducted among returning residents and support providers in coastal areas of Fukushima Prefecture, from which application functions and layout were decided. App functions were included to estimate external exposure, monitor health, and facilitate interactive health counseling.

Emergency Hospital Evacuation From a Hospital Within 5 km Radius of Fukushima Daiichi Nuclear Power Plant: A Retrospective Analysis of Disaster Preparedness for Hospitalized Patients.

Emergency evacuation during disasters may have significant health impacts on vulnerable populations. The Japanese Government issued evacuation orders for surrounding residents of the Fukushima Daiichi nuclear power plant (FDNPP) immediately after the March 11, 2011, nuclear accident. Little is known of difficulties associated with the disaster-specific evacuation from health care facilities located in this area. Among the 338 patients hospitalized at Futaba Hospital, located 4.6 km west of FDNPP, at the time of the accident, 39 patients (11.5%), predominantly critically ill patients who were bedridden or disabled, died before the evacuation was completed. The shortage of hospital staff and disruption of infrastructure resulted in a lack of adequate care provision, such as infusion therapy or sputum suctioning, leading to premature death of some hospitalized patients during the emergency hospital evacuation. As hospital evacuation is sometimes unavoidable during disasters, potential health impacts of hospital evacuation should be recognized and reflected in disaster preparedness plans.

Tailoring Digital Tools to Address the Radiation and Health Information Needs of Returnees after a Nuclear Accident.

Digital tools are increasingly used for health promotion, but their utility during recovery from a nuclear disaster has yet to be established. This study analysed differences in knowledge, attitude, and practice (KAP) toward digital tools for radiation protection and health promotion, and preferences for specific application functions, among cohorts living within and outside areas affected by the Fukushima Daiichi nuclear power station (FDNPS) accident. A needs assessment was conducted by internet survey, and responses from those affected (N = 86) and not affected (N = 253) were compared and quantified by an adjusted odds ratio (aOR), using logistic regression analyses. KAP toward the radiation-related application in the affected group had an aOR of 1.95 (95% confidence interval (CI) = 1.12-3.38) for knowledge, and 5.71 (CI = 2.55-12.8) for practice. Conversely, toward the health-related application, the aOR of the affected group was 0.50 (CI = 0.29-0.86). The preference in the affected group was significantly lower for two application functions related to radiation measurement and two health-related functions (one about the effects of radiation in general and another about personal health advice in general): aOR range 0.43-0.50. Development of specific applications incorporating the findings from this survey was intended to foster a locally appropriate eHealth environment during recovery from the FDNPS accident.

Needs Survey for Health Support Application Development Project for Residents Returning from Evacuation After the Fukushima Nuclear Accident.

The purpose of this study was to identify the needs of stakeholders in developing a mobile application (MP) to be used by returning residents and providers of healthcare and medical/social services. The needs assessment of the residents revealed that among the elderly, ownership of smartphones and tablets was low and they were less likely to use the applications themselves.

Case review of severe acute radiation syndrome from whole body exposure: concepts of radiation-induced multi-organ dysfunction and failure.

Acute radiation syndrome (ARS) due to whole body exposure (WBE) presents various clinical pictures, occasionally leading to fatal consequences. In this report, the literature providing details of the clinical course of severe ARS owing to WBE is reviewed and the lessons learned from recent accidents are discussed, to better prepare for another radiological event. Studies investigating radiological accidents that provided details of medical care for severe ARS were searched in official reports from the International Atomic Energy Agency and through the databases of PubMed, Medline, CiNii and Google Scholar and reviewed. Four fatal cases of severe ARS due to WBE in Soreq 1990 and Nesvizh 1992, and two cases in JCO Tokaimura 1999 were reviewed. A common set of medical interventions was carried out, that put a focus on medical management assuming the occurrence of hematopoietic disorders. However, clinicians were faced with a mixture of chronic hematological and non-hematological events including persistent gastrointestinal disorders, gradual and progressive skin disorders, liver and renal dysfunction and respiratory failure. Clinical pictures following high-dose WBE have become more complicated as treatment modalities improve. To address these issues, a concept of severe ARS due to WBE has been proposed with respect to radiation-induced multi-organ dysfunction syndrome (RI-MODS) and failure (RI-MOF). These patients need to be managed at institutions where multidisciplinary, resource-intensive therapy can be provided.

Evacuation after a nuclear accident: Critical reviews of past nuclear accidents and proposal for future planning.

Standards and guidelines for preparedness and response in the case of a nuclear accident cover radiation protection, health management and communication with affected populations. Decision makers use these recommendations to decide on measures that protect people residing around a nuclear power plant that suffers an accident from radiation exposure; for example, sheltering, evacuation and relocation. While technological and radiological criteria exist for these protective measures, studies on past radiological and nuclear emergencies have shown that evacuation and relocation result in serious health effects; this needs to be considered in accident preparedness and responses in the future. Within the framework of the Nuclear Emergency Situations Improvement of Medical and Health Surveillance (SHAMISEN) (Ohba et al., 2020), a critical review of recommendations and experiences of previous major nuclear accidents was conducted, and the current paper focuses on the lessons learned about evacuation and relocation. We reviewed the contents of official documents and literature relating to the evacuation and relocation of residents, and to the evacuation of medical and other facilities in the three largest nuclear accidents to date: the Three Mile Island accident, Chernobyl accident, and Fukushima accident. We developed recommendations classified into the preparedness phase, early and intermediate phases, and recovery phase after an accident. In the cases of Three Mile Island and Fukushima, the evacuation area was set at 8-10 km from the nuclear power plant in the disaster prevention plan, and emergency responses, such as information provision and evacuation, had been developed only in this area. When the Fukushima accident occurred, evacuation beyond this area was urgently planned or instructed, resulting in marked confusion, such as forced multiple evacuations and relocations for long periods. Furthermore, information was lacking, and personal protective measures such as respiratory protection and iodine prophylaxis were not applied to evacuees. In hospital and facility evacuation, it became more difficult to implement evacuation owing to a lack of advance planning and support in the event of the accident. In Fukushima, more than 60 people in hospitals and nursing care facilities died during or soon after evacuation. In long-term relocation, in addition to continuing adverse mental effects, there were health effects relating to relocation, such as lifestyle-related disease. The return of residents to the evacuation area required many issues, such as a delayed recovery of the living environment, to be overcome in addition to measures to reduce the effects of radiation. Recommendations for evacuation in the SHAMISEN framework were developed (SHAMISEN Consortium, 2017; Liutsko et al., 2020) from these lessons of previous accidents.

Living conditions and health status of populations living in territories impacted by nuclear accidents - Some lessons for developing health surveillance programme.

This paper explores how health concerns of populations living in contaminated areas following radiological accidents can be considered in developing health surveillance. The research was performed in the framework of the SHAMISEN project, and aimed at identifying the impacts on, and challenges associated with, living and social conditions of affected populations. These objectives were achieved through the analysis of specific Case Studies in different situations observed after the Chernobyl accident (Belarus and Norway) and the activities carried out after the Fukushima accident. It incorporates an analysis of testimonies of medical experts and local stakeholders from contaminated territories in Japan within two Case Studies as well as through a dedicated workshop jointly organised with Fukushima Medical University in Japan in March 2016. The analysis addresses the following topics:Thus, this paper outlines key lessons learned from each of these topics, by providing tangibles examples from the analysis of the various Case Studies.

Health and Medical Issues in the Area Affected by Fukushima Daiichi Nuclear Power Plant Accident.

Futaba County was the area most affected by the 2011 Fukushima Daiichi nuclear power plant accident. To understand issues around the re-development of the medical system, we investigated the post-accident changes in medical needs and the system's transition. We analyzed reports from Fukushima Prefecture and local municipalities, ambulance transport data from the Futaba Fire Department, and patient data from Futaba Medical Center (FMC). After the accident, all medical institutions were closed, and the number of ambulance use dropped sharply. With the lifting of evacuation orders beginning in 2014, the amount of ambulance use increased at an annual rate of about 10%. Early on, the proportion of trauma caused by occupational and traffic accidents increased rapidly to more than 30%. As residents returned, the proportion related to endogenous diseases (most commonly respiratory) increased. Soon after the FMC opened in 2018, the majority of the patients were in their 60s, and by 2019 the proportion of patients in their 80s markedly increased. The return of the residents as well as ongoing decontamination and reconstruction projects were related to changes in the demographics of patients and the types of injuries and illnesses observed.

Lessons from past radiation accidents: Critical review of methods addressed to individual dose assessment of potentially exposed people and integration with medical assessment.

The experiences of the Chernobyl and Fukushima nuclear accidents showed that dosimetry was the essential tool in the emergency situation for decision making processes, such as evacuation and application of protective measures. However, at the consequent post-accidental phases, it was crucial also for medical health surveillance and in further adaptation to changed conditions with regards to radiation protection of the affected populations. This review provides an analysis of the experiences related to the role of dosimetry (dose measurements, assessment and reconstruction) regarding health preventive measures in the post-accidental periods on the examples of the major past nuclear accidents such as Chernobyl and Fukushima. Recommendations derived from the review are called to improve individual dose assessment in case of a radiological accident/incident and should be considered in advance as guidelines to follow for having better information. They are given as conclusions.

The SHAMISEN Project: Challenging historical recommendations for preparedness, response and surveillance of health and well-being in case of nuclear accidents: Lessons learnt from Chernobyl and Fukushima.

Experience suggests that current nuclear accident response planning in European countries mostly has a technical focus, with less attention paid to social, psychological and ethical issues. Information provided tends to be directed towards decisions made by experts, rather than for the support of affected populations. The SHAMISEN (Nuclear Emergency Situations - Improvement of Medical And Health Surveillance) consortium, composed of close to 50 experts from 10 countries, performed a critical review of current recommendations and experiences regarding dose assessment and reconstruction, evacuation decisions, long-term health surveillance programmes and epidemiological studies. The review included case studies and lessons drawn from the living conditions and health status of populations affected by the Chernobyl and Fukushima accidents, taking an integrative approach to health and well-being. Based on this work, SHAMISEN developed a series of comprehensive recommendations aimed at improving the preparedness, response, long-term surveillance and living conditions of populations affected by past or future radiation accidents, in a manner responding to their needs, while minimising unnecessary anxiety.

Nested matched case control study for the Japan Fukushima Health Management Survey's first full-scale (second-round) thyroid examination.

Since Fukushima nuclear accident in 2011, thyroid ultrasound examinations have been conducted. The first full-scale examination detected 71 thyroid-cancer cases. This study examined whether radiation exposure was associated with thyroid-cancer incidence.Subjects were participants in the baseline screening and newborns during the 2011 fiscal year. Under nested matched case-control study design, 10 controls per each case were selected by matching the age, sex, baseline screening results, and interval between examinations. With 3 dose levels of external radiation: 1.3 + mSv (upper), 0.8 to 1.3 (middle), and 0.0 to 0.8 (reference), we applied 2 logistic models adjusting for 3 participation-proportions (primary, secondary, and fine-needle aspiratory cytology), overweight, and the B-result of baseline screening (Model 1), and past medical history, family history of thyroid cancer, and frequencies of eating seafood and seaweed in addition to the parameters in Model 1 (Model 2). We examined each model in 3 ways: (a) excluding subjects with a missing radiation exposure dose; and substituting (b1) median or (b2) mean dose of the municipality with missing dose.Odds ratios (ORs) of middle-dose exposure were (a) 1.35 (0.46-3.94), (b1) 1.55 (0.61-3.96), and (b2) 1.23 (0.50-3.03) for Model 1, and (a) 1.18 (0.39-3.57), (b1) 1.31 (0.49-3.49), and (b2) 1.02 (0.40-2.59) for Model 2. For upper-dose exposure, similar results were obtained. Past medical history was significantly associated (odds ratio  = 2.04-2.08) with both (b1) and (b2) in Model 2.No significant associations were obtained between the external radiation exposure and thyroid-cancer incidence.

Factors Influencing the Proportion of Non-examinees in the Fukushima Health Management Survey for Childhood and Adolescent Thyroid Cancer: Results From the Baseline Survey.

BACKGROUND: After the Fukushima Daiichi Nuclear Power Plant accident, a preliminary ultrasound-based screening for thyroid cancer was conducted to establish a baseline for subsequent evaluations. In this survey, we assessed the relationship between the proportion of non-examinees and characteristics of the target populations. METHODS: After summarizing a regional difference of non-examinees among the population of 359,200 (primary evaluation) and 2,246 (confirmatory testing) individuals who were living in Fukushima Prefecture on March 11, 2011, we estimated odds ratios (ORs) for each characteristic, including age, sex, area of residence, and moving after the accident, based on the proportion of non-examinees for the primary examination and the confirmatory testing, using a multivariate logistic regression model. RESULTS: The dataset included 64,117 non-examinees (primary evaluation) and 194 (confirmatory testing). The logistic regression result indicated that girls were not likely to be non-examinees compared to boys, with adjusted OR of 0.80 (95% confidence interval [CI], 0.78-0.81) for the primary evaluation. Odds were lowest for children 6-10 years old (OR 0.26; 95% CI, 0.25-0.27), and higher for those 11-15 years old (OR 1.28; 95% CI, 1.25-1.32) and over 16 years old (OR 5.30; 95% CI, 5.16-5.43) when compared to children 0-5 years old. Individuals residing in the western part of the prefecture showed higher ORs. There was a higher proportion of non-examinees among those who moved after the accident compared to those who did not in the primary evaluation (OR 1.72; 95% CI, 1.64-1.79). CONCLUSIONS: In addition to demographic characteristics, a change of residence could be a potential factor that influenced the proportion of non-examinees. Our results will help proper interpretation of reports and prospective management of the survey.

External Radiation Dose, Obesity, and Risk of Childhood Thyroid Cancer After the Fukushima Daiichi Nuclear Power Plant Accident: The Fukushima Health Management Survey.

BACKGROUND: The 2011 Great East Japan Earthquake led to a nuclear accident at Fukushima Daiichi Nuclear Power Plant. This study examines the associations of radiation dose and lifestyle factors with incidence of thyroid cancer in Fukushima. METHODS: We designed a prospective study with 300,473 participants aged 18 years or younger, who underwent thyroid examinations from October 2011. Follow-up surveys were conducted through June 2017, and 245,530 participants (123,480 men and 122,050 women, 82% follow-up) received follow-up examinations. Fukushima Prefecture was divided into five areas based on individual external radiation dose. We calculated relative risks and 95% confidence intervals (CIs) for thyroid cancer in each area, with area of lowest dose as reference, using age-adjusted Poisson regression models. We also calculated risks associated with overweight and obesity. RESULTS: The incidence per 100,000 for Groups A (highest dose), B, C, D, and E (lowest dose) were 13.5, 19.2, 17.3, 9.0, and 8.3, respectively. Compared with Group E, the age-adjusted risks (95% CIs) were 1.62 (0.59, 4.47) for group A, 2.32 (0.86, 6.24) for group B, 2.21 (0.82, 5.94) for group C, and 1.02 (0.36, 2.86) for group D. Obesity was positively associated with thyroid cancer incidence; the multivariable-adjusted risk of thyroid cancer was 2.23 (1.01, 4.90) for obese individuals compared with nonobese individuals. CONCLUSION: Regional differences in radiation dose were not associated with increased risk of thyroid cancer among children in Fukushima within 4 to 6 years after the nuclear power plant accident. Obesity may be an important factor for further follow-up in Fukushima.

Comparison of three video laryngoscopes and direct laryngoscopy for emergency endotracheal intubation: a retrospective cohort study.

OBJECTIVE: Video laryngoscopes are used for managing difficult airways. This study compared three video laryngoscopes' (Pentax-Airway Scope [Pentax], King Vision[King] and McGrath MAC [McGrath]) performances with the Macintosh direct laryngoscope (Macintosh) as emergency tracheal intubations (TIs) reference. DESIGN: Retrospective cohort study. SETTING: The emergency department (ED) and the intensive care unit (ICU) of two Japanese tertiary-level hospitals. PARTICIPANTS: All consecutive video-recorded emergency TI cases in EDs and ICUs between December 2013 and June 2015. PRIMARY OUTCOME MEASURES: The primary study endpoint was first-pass intubation success. A subgroup analysis examined the first-pass intubation success of expert versus non-expert operators. A logistic regression analysis was performed to identify the predictors of first-pass intubation success. RESULTS: A total of 287 emergency TIs were included. The first-pass intubation success rates were 78%, 58%, 78% and 58% for the Pentax, King, McGrath and Macintosh instruments, respectively (p=0.004, Fisher's exact test). The non-expert operators' success rates were significantly higher (p=0.00004, Fisher's exact test) for the Pentax (87%) and McGrath (78%) instruments than that for the King (50%) and Macintosh (46%) instruments, unlike that of the experts (67%, 67%, 78% and 78% for Pentax, McGrath, King and Macintosh, respectively; p=0.556, Fisher's exact test). After TI indication, difficult airway characteristics, and expert versus non-expert operator parameters adjustments, the Pentax (OR=3.422, 95% CI 1.551 to 7.550; p=0.002) and McGrath (OR= 3.758, CI 1.640 to 8.612; p=0.002) instruments showed significantly higher first-pass intubation success odds when compared with the Macintosh laryngoscope (reference, OR=1). The King instrument, however, (OR=1.056; 95% CI 0.487 to 2.289, p=0.889) failed to show any significant superiority. CONCLUSION: The Pentax and McGrath laryngoscopes showed significantly higher emergency TI first-pass intubation success rates than the King laryngoscope when compared with the Macintosh laryngoscope, especially for non-expert operators. TRIAL REGISTRATION NUMBER: UMIN000027925; Results.

Incidence of Thyroid Cancer Among Children and Young Adults in Fukushima, Japan, Screened With 2 Rounds of Ultrasonography Within 5 Years of the 2011 Fukushima Daiichi Nuclear Power Station Accident.

Importance: Ultrasonographic (US) screening for thyroid cancer was performed in the Fukushima Health Management Survey after the 2011 Fukushima Daiichi nuclear power station accident. Clinical characteristics of thyroid cancers screened by US among children and young adults during the first 5 years after the accident were analyzed. Objectives: To evaluate the number of detected thyroid cancers by age group within 5 years of the Fukushima Daiichi nuclear power station accident and to compare the basic clinical characteristics and demographic patterns in first- and second-round examinations. Design, Setting, and Participants: In this observational study, 324 301 individuals 18 years or younger at the time of accident were included. Patients received a cytologic diagnosis of malignant or suspected malignant thyroid cancer during the first (fiscal years 2011-2013) or second round (fiscal years 2014-2015) of screening. Number of detected cases of cancer was evaluated, correcting for the number of examinees by age group at the time of the accident and for the incidence of detected cancers according to age group at the time of the screening (age groups were divided into 3-year intervals). Results were compared using the age-specific incidence of unscreened cancers from a national cancer registry. Main Outcomes and Measures: Clinical baseline characteristics of the patients and the age-specific number and incidence of thyroid cancers detected during the second round. Results: Among 299 905 individuals screened in the first round (50.5% male; mean [SD] age at screening, 14.9 [2.6] years), malignant or suspected thyroid cancer was diagnosed in 116. Among 271 083 individuals screened in the second round (50.4% male; age at screening, 12.6 [3.2] years), malignant or suspected thyroid cancer was diagnosed in 71. The most common pathologic diagnosis in surgical cases was papillary thyroid cancer (149 of 152 [98.0%]). The distribution pattern by age group at the time of the accident, where the number of detected thyroid cancer cases was corrected by the number of examinees, increased with older age in both screening rounds. This demographic pattern was similar between the first and second examinations. The distribution pattern of the incidence rate by age group at the time of screening in the second round also increased with older age. The incidence rate detected by screening was 29 cases per 100 000 person-years for those aged 15 to 17 years, 48 cases per 100 000 person-years for those aged 18 to 20 years, and 64 cases per 100 000 person-years for those aged 21 to 22 years. Conclusions and Relevance: Large-scale mass US screening of young people resulted in the diagnosis of a number of thyroid cancers, with no major changes in overall characteristics within 5 years of the 2011 Fukushima nuclear power station accident. These results suggest that US screening can identify many detectable cancers from a large pool of nonclinical and subclinical thyroid cancers among individuals of a relatively young age, in an age-dependent manner.