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Background: Earlier studies have indicated the BA.5 sublineage of Omicron variant strain of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) as more infective than BA.2. Object: This study estimated BA.5 infectivity while controlling other factors possibly affecting BA.5 infectivity including vaccine effectiveness, waning effectiveness, other mutated strains, Olympic Games, and countermeasures. Method: The effective reproduction number R(t) was regressed on shares of BA.5 and vaccine coverage, vaccine coverage with some delay, temperature, humidity, mobility, shares of other mutated strains, countermeasures including the Go to Travel Campaign, and the Olympic Games and associated countermeasures. The study period was February 2020–July 22, 2022, using data available on August 12, 2022. Results: A 120 day lag was assumed to assess waning. Mobility, some states of emergency, vaccine coverage and those with lag, and the Delta and Omicron BA.2 proportions were found to be significant. The omicron BA.1 proportion was significant, but with an unexpected sign. The estimated coefficient of BA.5 was negative but not significant. The Go to Travel Campaign was significantly negative, indicating reduced infectivity. The Olympic Games were negative but not significant, indicating that they did not raise infectivity. Discussion: The obtained estimated results show that BA.5 did not have higher infectivity than the original strain. It was lower than either Delta or Omicron BA.2 variant strains. That finding might be inconsistent with results obtained from earlier studies. This study controlled several factors potentially affecting R(t), though the earlier studies did not. Therefore, results from this study might be more reliable than those of earlier studies.

As of the end of November, 2021, the rate of completion for second-dose COVID-19 vaccine administration was almost 80% in Japan. We evaluated waning COVID-19 vaccine effectiveness in Japan, controlling for mutated strains, the Olympic Games, and countermeasures. The effective reproduction number R(t) was regressed on current vaccine coverage and data of a certain number of days prior, as well as shares of mutated strains, and an Olympic Games dummy variable along with data of temperature, humidity, mobility, and countermeasures. The study period was February, 2020 through November 4, as of November 25, 2021. Estimation results indicate that vaccine coverage of more than 90 days prior raises R(t) significantly. Especially, vaccine coverage with 90 or 120 days prior cancelled vaccine effectiveness completely. Results indicate significant waning of vaccine effectiveness from 90 days after the second dose.

Background: By March, 2021, the COVID-19 outbreak had reached its highest peak at the end of December, 2020. Nevertheless, no remarkable excess mortality attributable to COVID-19 has been observed. Object: We sought to quantify excess mortality in April using the National Institute of Infectious Diseases (NIID) model. Method: We applied the NIID model to deaths of all causes from 1987 through February, 2021 for all of Japan and through October for Tokyo. Results: Results obtained for Japan show very few excess mortality cases in August and October, 2020, estimated respectively as 12 and 104. However, in Tokyo, 595 cases of excess mortality were detected during August and October: they were, respectively, 3.1% and 1.7% of baseline numbers. Discussion and Conclusion: We detected considerable excess mortality in Tokyo but not throughout Japan. Continued careful monitoring of excess mortality of COVID-19 is expected to be important.

Background In Japan, measles elimination was confirmed in March 2015. Nevertheless, some outbreaks with cases imported from abroad were reported even after certification. A large rubella outbreak has been occurring since 2017. This study examines measurement of the speed of attenuation of antibody titer for a measles virus comparison with rubella virus. Method Student subjects born from April 2, 1996 through April 1, 2000 were selected at Ibaraki Prefectural University of Health Sciences for this study: 177 for measles and 114 for rubella. They had available dates of additional immunization and antibodies in the following period and were judged as requiring additional immunization. We used enzyme immunoassay for IgG antibody testing. We regressed post-antibody titers of measles or rubella on pre-antibody titers and functions of duration between inoculation to post-evaluation. Functions of duration were selected according to the adjusted coefficient of determination. Results For measles, only a linear term of duration or log of duration was found to be significant without the quadratic terms. For rubella, we selected a five-order linear model which indicated that titer after vaccination would converge to 19.2. Discussion Results demonstrate that measles antibody decreased monotonically. If the pre-antibody titer was 15, vaccination raised titer quickly to 26; then it attenuated by 0.014 per day. Antibody titer is expected to be less than 16, which is the protection level of titer, after 704 days. For rubella, however, when pre-vaccination titer was evaluated at its average, the lower limit was 19.2. Therefore, protection can be maintained for a long time. This difference might reflect some circumstances of outbreaks of the respective diseases. Conclusion. This report describes the speed of attenuation and the epidemiological situation. The speed of attenuation can be expected to rise. Therefore, additional vaccination every several years might be necessary to maintain a protection level if a disease is almost eliminated.

In Tokyo, Japan, coronavirus disease 2019 (COVID-19) cases have been increasing gradually since late March 2020. This study was aimed to predict the effects of self-restraint against excursions in Tokyo before the emergency declaration of April 7, 2020. Data of symptomatic patients collected between January 14 and March 28, 2020, in Tokyo, were used to formulate a susceptible–infected–recovered (SIR) model using three age classes and estimate the basic reproduction number (R0). Based on the estimated R0, we inferred outbreak outcomes and medical burdens if self-restraint against excursions had not been enacted. Thereafter, we estimated the effects of self-restraint against excursions. The results suggested an R0 value of 2.86, with a 95% confidence interval of 2.73–2.97. It is likely that the exhaustion of medical resources could have occurred on April 28, 2020, if no self-restraint against excursions had occurred. If self-restraint against excursions had been enacted from April 6, 2020, and more than 60% of trips outside the home had been restricted voluntarily, medical care services would then have been predicted to be maintained. Our suggestion might have contributed to countermeasures against COVID-19 in Tokyo.

Control of infectious diseases requires switching from usual hygiene such as water wiping and cleaning, to control measures including appropriate and aggressive disinfection using 70% alcohol and/or hypochlorous acid depending on the pathogen. Nevertheless, some nursery schools might not understand or select proper disinfectant methods. A survey was administered by the local government of Ibaraki prefecture, Japan in January 2018 to all 456 nursery schools in Ibaraki prefecture. The surveyed items were the number of nursery teachers, usual manual hygiene among children, usual disinfection for lavatories, diaper changing spaces, tables used by children for meals, and classroom floors when there was no vomiting in the facilities and no outbreak in surrounding area. Moreover, it asked about disinfection procedures if children vomited during a community outbreak of gastroenteritis infection. We defined proper use for usual disinfection of a lavatory or diaper changing space as chlorine-based disinfectant including hypochlorous acid or 70% alcohol according to guidelines. Overall, 403 nursery schools responded to the survey. All nursery schools implemented usual hand hygiene. Association between proper disinfection and the size of nursery schools was not significant. Moreover, association between proper disinfection and nursery schools with nurse presence was not found to be significant.

In Japan, the reported cases of syphilis have been increasing since 2011 especially in large cities such as Tokyo. The objective of this study was to evaluate the risk of HIV infection for syphilis co-infection on the population of Tokyo, Japan. We analyzed data of syphilis cases obtained from additional surveillance by the Tokyo Metropolitan Government in 2018, including those with human immunodeficiency virus (HIV) infection as well as data of HIV/acquired immunodeficiency syndrome (AIDS) cases during 1985-2017. We calculated the incidence of symptomatic syphilis cases among HIV-infected or non-HIV-infected individuals. Similarly, we calculated the incidence of syphilis, including asymptomatic cases, among each population. The relative risk of HIV infection for syphilis, including or excluding asymptomatic syphilis cases, was estimated. The relative risk was calculated by dividing the incidence of syphilis in the HIV-infected population by that in the non-HIV-infected population. Of the 1,775 syphilis cases reported in 2018, 172 cases were infected with HIV, 575 cases were uninfected, and the remainder were either unknown or not reported. The cumulative number of HIV/AIDS cases during 1985-2017 in Tokyo was 9,629; among them, 172 were co-infected with syphilis. The relative risk of HIV infection for syphilis was estimated as 423.29 if asymptomatic syphilis cases were included, and 372.37 if they were excluded. These results showed an extremely high risk of HIV infection. Since many syphilis cases have unknown or unreported HIV infection status, reduction of these cases might contribute to more reliable estimation of HIV infection risk.

Background: Palivizumab were used for the premature infant or a high-risk infant with congenital heart disease. However, recently outbreak pattern of respiratory syncytial (RS) virus infection has been varying year by year. Moreover, it also has some regional difference. Therefore, the object of the present study was to develop early detection of the timing of that outbreak had started in each prefecture. Method: We used data in National Official Sentinel Surveillance for Infectious Diseases (NOSSID). Study period was March 16th, 2011 to December 30th, 2018. We defined stating period to initiate to take palivizumab as 8 - 12 weeks before from the peak of outbreak. We estimated whether the week is included in starting period or not from April 1st to the peak of outbreak by the past number of patients of RS virus infection on week and its squared. Additionally, we have to take delay in NOSSID into consideration. Results: In nationwide, the last two seasons, the model predicted precisely the starting period. At prefectural level, the model predicted the starting period precisely in 16.6% of all year and prefectures pairs. When we consider the delay in NOSSID into consideration, the patients can start to take in 14.9% of all year and prefectures pairs. Discussion and Conclusion: The result of the probability model was not good, and thus we have to develop more sophisticated model for prediction at prefecture level.

Object: Prediction of the COVID-19 epidemic represents a matter of concern not only for public health or medicine but also for Earth’s general population. This study predicts outbreaks in Wuhan and in Japan as of 11 February, 2020.Method: We applied a simple SIR model to data published by Hubei public health authorities. Moreover, into the model, we incorporate mild and asymptomatic cases from experiences of Japanese residents of Wuhan up to the outbreak. Finally, we predict an outbreak in Japan based on 10,000 iterations of a simulation conducted under the assumption of infected people including mild cases visiting Japan according to the estimated distribution of patients in Wuhan since the date on which the initial case occurred to the date when travel from Wuhan to Japan was suspended. Results: Results suggest the basic reproduction number, R0, as 2.84; its 95% confidence interval (CI) was [2.35, 3.33]. The peak is estimated to be reached on March 11. Its 95% CI peak date is 29 February to 27 March. The 95% CI peak date in Japan is 26 April to 2 May. The greatest number of patients at the peak with severe symptoms was estimated as 858.3 thousand. Discussion and Conclusion: Our obtained R0 of 2.84 approximates an earlier estimate. We predicted the greatest number of patients at the peak with severe symptoms as 858.3 thousand in Japan. This number is 63% greater than the highest daily peak of influenza.

BackgroundOn April 25, 2021, the third state of emergency was declared in Japan. Drinking alcohol at restaurants and bars was banned.ObjectWe used published data to evaluate drinking ban effects.MethodWe bootstrapped the data and evaluated the risk ratio for drinking compared with non-drinking during group dining with similar frequency and numbers of participants.ResultsThe 99% lower bound of the bootstrapped distribution of the risk ratio was less than one. Therefore the null hypothesis, that incidence in the two styles of group dining were the same, cannot be rejected.Discussion and ConclusionResults constitute no clear evidence indicating a risk of drinking alcohol in groups. However, further analyses using collected data are necessary. Moreover, risks posed by the number of group diners or their dining frequency must be evaluated.

BackgroundOmicron variant strain dominated since the beginning of 2022. Its infectivity was supposes to be higher than Delta variant strain or strains in past.ObjectWe estimated prevalence of omicron variant strain, particularly bA.2 variant and COVID-19 vaccine effectiveness of the third dose in Japan as well as controlling for waning of second dose of vaccine, other mutated strains, the Olympic Games, and countermeasures.MethodThe effective reproduction number R(t) was regressed on shares of omicron variant strain and bA.2 and vaccine coverage of the third dose, as well as along with data of temperature, humidity, mobility, share of the other mutated strains, and an Olympic Games and countermeasures. The study period was February, 2020 through February 21, 2022, as of March 15, 2022.ResultsEstimation results indicated that waning of the second dose vaccine e with 150 days prior was the most appropriate specification. Moreover, bA.2 of omicron variant strain has higher infectively than other variant strain or traditional strain.DiscussionBecause of data limitation since emerging bA.2, the estimated its infectively will change over time.

SummaryBackgroundTo avoid exhaustion of medical resources by COVID-19 care, policy-makers must predict care needs, specifically estimating the proportion of severe cases likely to require intensive care. In Osaka prefecture, Japan, the number of these severe cases exceeded the capacity of ICU units prepared for COVID-19 from mid-April, 2021.ObjectiveThis study used a statistical model to elucidate dynamics of severe cases in Osaka and validated the model through prospective testing.MethodsThe study extended from April 3, 2020 through April 26, 2021 in Osaka prefecture, Japan prefecture. We regressed the number of severe cases on the number of severe cases the day prior and the newly onset patients of more than 21 days prior.ResultsWe selected the number of severe cases the day prior and the number of newly onset patients on 21 and 28 days prior as explanatory variables for explaining the number of severe cases based on the adjusted determinant coefficient. The adjusted coefficient of determination was greater than 0.995 and indicated good fit. Prospective out of sample three-week prediction forecast the peak date precisely, but the level was not t.Discussion and ConclusionA reason for the gap in the prospective prediction might be the emergence of variant strains.

Background: Earlier study without actual trial indicated that caregivers needed delivery of information about outbreak situations independently of their job status. This report describes, for about two months in winter, actual delivery outbreak information to families with preschool children. The study objective was to confirm the usefulness of this information delivery. Method: Participants receiving outbreak information were recruited from the Child Care Support Service in a ward in Tokyo, Japan. Outbreak information was obtained from the Nursery School Absenteeism Surveillance System (NSASSy) covering approximately 40% of all nursery schools in Japan, prescription surveillance and other resources. Delivery of outbreak information started in December 2017 and ceased at the end of February in 2018. After the delivery period, a questionnaire survey was administered to participants. Results: For this area, NSASSy showed the most dominant disease was influenza, with 707 patients, followed by group A streptococcal pharyngitis with 98 patients. The outbreak peak was inferred to be as Monday, 22 January, and it was announced by e-mail on 23 January. Of the 202 persons joined this trial, 60 participants responded to the questionnaire survey after the delivery period. Of those respondents, 98% wanted delivery of that information to continue. Conclusion: We found that almost all respondents confirmed usefulness of the information about infectious diseases which was delivered.

Background and objectiveIn Japan, routine administration of two-dose immunization for varicella to one-year-old children was introduced in October, 2014. The objective of this study was measurement of the effectiveness of routine two-dose immunization for varicella to onset and assessment of severity in a nursery school setting.MethodThe study period extended from the beginning of April, 2017 through March, 2018. The study area was Nursery school B in a city A. Subjects were 120 children in all. We analyzed vaccine efficacy (VE) as an observational study and assessed severity using Fisher’s exact test. We also assessed VE for severity using linear regression. Severity was defined as the length of school absence attributable to varicella infection.ResultsFor one dose or more, VE was 48.1% for all ages and 49.2% among children three years old and older. No significant VE was found. Vaccination using one dose or more can reduce severity significantly.Discussion and conclusionLow VE was found in a nursery school setting, although results were not significant. VE for severity was confirmed, but a second dose might not reduce severity.

Background: Infectiousness of COVID-19 by infected place might be different. However, studies of such infectiousness have not been reported. Object: The object of this study was estimation of reproduction numbers by infected place. Method: We ignore patients who infected no one because their reliability might be lower than that of patients who infected more than one person. We estimated the reproduction number from the histogram of the number of the infected people by the same patient, assuming that the histogram follows an exponential distribution. Results: Entertainment at night was the highest and facility for elderly people and hospital followed. Home was the lowest and nursery school and workplace followed. Discussion and Conclusion: The counter measure under the second emergency status declaration targeted restaurant. However, infectiousness at restaurant was not so high and comparable as university or karaoke and not significantly difference from at home which is the lowest infectiousness place.

BackgroundA variant strain of SARS-CoV-2, VOC202012/01, emerged in the UK in September, 2020. Its infectiousness was estimated as higher than that of the original strain.ObjectWe estimated the infectiousness of the variant strain of SARS-CoV-2 in comparison to that of the original strain under conditions prevailing in Japan.MethodsWe estimated infectiousness through a simple susceptible–infected–recovered (SIR) model by strain. The study period was March 1–28, 2020. The information used for the study was available as of April 3, 2020.ResultsThe estimated reproduction number of the SARS-CoV-2 variant strain was 1.799; its 95% CI was [1.642, 1.938]. The onset date of the first case in Japan was estimated as December 4 ([November 16, December 14]), 2020. However, infectiousness of the original strain was estimated as 1.123 ([1.093, 1.166]).Discussion and ConclusionWe demonstrated that infectiousness increased by 0.684 or 60%, increasing from the original to the variant. That finding might be comparable to that of a study conducted in the UK. However, the difference must be monitored continuously and carefully.

SummaryBackgroundTo avoid exhaustion of medical resources by COVID-19, policy-makers must predict care needs, specifically the proportion of severe cases likely to need ventilator care.ObjectiveThis study was designed to use a statistical model to elucidate dynamics of severe cases in Tokyo and to discuss the timing of effective policy activation.MethodsThe study extended from April 27 through October 18, 2020 in Japan’s Tokyo Metropolitan area. Medical exhaustion was defined as use of more than half of the ventilator capacity available before the COVID-19 outbreak. We regressed the number of severe cases on the newly onset patients of more than 14 days prior. As earlier research indicated, the COVID-19 severity changed at the end of May. Therefore, we added dummy variables to reflect changing severity from June and its product with newly onset patients as the explanatory variable. Then we calculated the threshold using R(t): R(t)=0.99 for the number of patients 14 days prior was used as a threshold at which strong countermeasures should be activated to keep to avoid medical exhaustion.ResultsThe critical number signaling medical exhaustion in Tokyo was defined as 655 cases. We selected 15, 30, 60 and 90 days prior as explanatory variables for explaining the number of severe cases. A coefficient of determination larger than 0.95 was inferred as indicating good fit. The threshold was estimated as more than 4500 cases for R(t)=1.1 and monotonically decreasing by R(t) to be 600 cases for R(t)=2.5.Discussion and ConclusionResults showed that newly onset patients reported more than 14 days prior can explain the number of severe cases very well. We also confirmed the threshold number of patients 14 days prior by R(t) for which strong countermeasures should be activated to avoid medical exhaustion with R(t)=0.99. This method is expected to be useful for countermeasure activation policies for Tokyo.

BackgroundStrict countermeasures for COVID-19 outbreak such as lockdowns and voluntary restrictions against going out might have reduced mortality because of COVID-19 directly, but might have raised suicide rates.ObjectWe examined best policies for minimizing overall mortality attributable to COVID-19 directly, and excess mortality by suicide because of COVID-19.MethodWe regressed the estimated excess mortality attributable to suicide deaths against mobility-restrictive measures. Mortality attributable to COVID-19 directly was estimated through association between the effective reproduction number and mobility. We sought the best mobility restriction for minimizing overall deaths.ResultsSignificant association was found between mobility and suicide, but the data were very few. Results showed the best mobility level as 65.5, which represents a 34.5% reduction in mobility from the normal level.Discussion and ConclusionAn overly restrictive policy inducing lower than optimal mobility led to higher total mortality.

BackgroundCountermeasures against COVID-19 outbreak such as lockdown and voluntary restrictions against going out adversely affect human stress and economic activity. Particularly, this stress might lead to suicide.ObjectWe examined excess mortality attributable to suicide caused by COVID-19. Method: We applied the NIID model to suicide deaths from October 2009 through September, 2021 for the whole of Japan by gender. Effects of the great earthquake that struck in eastern Japan on March 11, 2011 were incorporated into the estimation model. Results: Significant excess mortality in suicide was found between July, 2020 and July, 2021 for both genders. However, in August and September, 2021, excess mortality in suicide was detected only in female. It was greater among females than among males. In total, 2950 excess cases of mortality were identified.Discussion and ConclusionExcess mortality during the four months was more than two times greater than the number of COVID-19 deaths confirmed by PCR testing. Countermeasures against COVID-19 should be chosen carefully in light of suicide effects.

Background In Japan, as a countermeasure against the COVID-19 outbreak, both the national and local governments issued voluntary restrictions against going out from residences at the end of March 2020 in preference to the lockdowns instituted in European and North American countries. The effect of such measures can be studied with mobility data, such as data which is generated by counting the number of requests made to Apple Maps for directions in select countries/regions, sub-regions, and cities. Objective We investigate the associations of mobility data provided by Apple Inc and an estimate an an effective reproduction number R(t). Methods We regressed R(t) on a polynomial function of daily Apple data, estimated using the whole period, and analyzed subperiods delimited by March 10, 2020. Results In the estimation results, R(t) was 1.72 when voluntary restrictions against going out ceased and mobility reverted to a normal level. However, the critical level of reducing R(t) to Conclusions We demonstrated that Apple mobility data are useful for short-term prediction of R(t). The results indicate that the number of trips should decrease by 10% until herd immunity is achieved and that higher voluntary restrictions against going out might not be necessary for avoiding a re-emergence of the outbreak.

BackgroundThe COVID-19 outbreak in Japan exhibited its third peak at the end of 2020. Mathematical modelling and developed AI cannot explain several peaks in a single year.ObjectThis study was conducted to evaluate a rule of thumb for prediction from past wave experiences.MethodWe rescaled the number of newly infected patients as 100% at the peak and checked similarities among waves. Then we extrapolated the courses of the third and later waves.ResultsResults show some similarity around the second and the third waves. Based on this similarity, we expected the bottom of the third wave will show 2131 newly positive patients including asymptomatic patients at around the end of February, 2021.Discussion and ConclusionWe can infer the course of the third wave from similarity with the second wave. Mathematical modelling has been unable to do it, even when AI was used for prediction. Performance of the rule of thumb used with human intelligence might be superior to that of AI under these circumstances.

BackgroundSince the emergence of COVID-19, cases of excess mortality from all causes have been very few in Japan.ObjectTo evaluate COVID-19 effects precisely, we specifically examine deaths caused by pneumonia and examine excess mortality attributable to pneumonia in Japan.MethodWe applied the NIID model to pneumonia deaths from 2005 up through November, 2020 for the whole of Japan. Introduction of routine pneumococcal vaccination for elderly people and revision in ICD10 were incorporated into the estimation model.ResultsNo excess mortality was found for 2020. However, negative excess mortality was observed as 178 in May, 314 in June, and 75 in July. No negative excess mortality was not found between August and November.Discussion and ConclusionSignificantly negative excess mortality might reflect precautions taken by people including wearing masks, washing hands with alcohol, and maintaining social distance. They reduced the infection risk not only of for COVID-19 but also of other infectious diseases causing pneumonia.

BackgroundInfectiousness of COVID-19 by age class inferred from the infection source and by infected people might be different. However, studies of such infectiousness have not been reported.ObjectThe object of this study was estimation of reproduction numbers by age class of the source of infection and the infected persons. To do so, after examining a new procedure for reproduction number estimation, we checked infected places by age class of the source of infection and the infected persons.MethodWe ignore patients who infected no one because their reliability might be lower than that of patients who infected more than one person. We estimated the reproduction number from the histogram of the number of the infected people by the same patient, assuming that the histogram follows an exponential distribution.Discussion and ConclusionThe obtained results demonstrated that the effective reproduction numbers for infection from children were very low. They were higher among adult and elderly people than among the same age class. Moreover, although the highest and second-highest infected places were ‘other’ and ‘at home’ with some exceptions, the data for infection at hospitals were remarkable among adults and elderly people. Among elderly people, infection at facilities for elderly was also high. Infections at nursing schools, schools, restaurants, and entertainment venues at night were negligible.

BackgroundSome aspects of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission in children and adults remain unclear. This report describes different SARS-CoV-2 transmission patterns by age group in Japan.Methods and findingsThis retrospective observational case series study analyzed transmission patterns of real-time polymerase chain reaction (RT-PCR)-confirmed SARS-CoV-2 infections found by local health authorities and commercial laboratories during January 14 through July 31, 2020 in Japan. After ascertaining the infection source for every symptomatic case as clusters at households, daycare facilities, schools, hospitals and workplaces etc., their associated transmission patterns were analyzed. Identified cases were divided into three groups: underage, < 20; adults, 20–59; and elderly people 60 years old and older. The reproductive number (R)s of respective transmission directions found for the respective age groups were compared.Of 26,986 total cases, 23,746 unknown cases were found, leaving 3,240 ascertained sources of infection (12.0%) comprising 125 (3.9%) underage, 2350 (72.5%) adult, and 765 (23.6%) elderly people. The respective Rs of underage infection sources directed to underage, adult, and elderly people were estimated respectively as 0.0415 (95% CI, 0.0138–0.0691), 1.11 (95% CI, 0.9171–1.3226), and 0.2811 (95% CI, 0.2074–0.3687). The respective Rs of adult infection source directed to underage, adult, and elderly people were estimated respectively as 0.0140 (95% CI, 0.0120–0.0162), 0.5392 (95% CI, 0.5236–0.5550), and 0.1135 (95% CI, 0.1074–0.1197). The respective Rs of elderly infection source directed to underage, adult, and elderly people were estimated as 0.065 (95% CI, 0.0039–0.0091), 0.3264 (95% CI, 0.3059–0.3474), and 0.3991 (95% CI, 0.3757–0.4229).ConclusionsThe main sources of SARS-CoV-2 infection were adults and elderly people. The R of underage people directed to adults was greater than 1 because of close familial contact but they were unlikely to become carriers transmitting SARS-CoV-2 because they accounted for a minority for transmissions. Apparently, SARS-CoV-2 was transmitted among adults and elderly people, suggesting that infection control of SARS-CoV-2 should be managed specifically by generation.

Background As countermeasures against the COVID-19 outbreak, sports and entertainment events were canceled (VEC) in Japan for two weeks from 26 February through 13 March. Moreover, most schools were closed (SC). Objective For this study, we estimated the basic reproduction number (R0) and SC and VEC effects. Method After constructing a susceptible–infected–recovered model with three age classes, we used data of symptomatic patients in Japan for 14 January through 24 March. The SC and VEC effects were incorporated into the model through changes in contact patterns and contact frequencies among age classes. Results Results suggest R0 as 2.56, with 95% CI of [2.51, 2.96] before SC and VEC. The respective effects of SC and VEC were estimated as 0.4 (95% CI [0.3, 0.5]) and 0.5 (95% CI [0.3, 0.7]). Conclusion The estimated R0 is similar to those found from other studies of China and Japan. Significant reduction of contact frequency has been achieved by SC and VEC. Nevertheless, its magnitude was insufficient to contain the outbreak.

Background To control the COVID-19 outbreak in Japan, sports and entertainment events were canceled and schools were closed throughout Japan from February 26 through March 19. That policy has been designated as voluntary event cancellation and school closure (VECSC). Object This study assesses VECSC effectiveness based on predicted outcomes. Methods A simple susceptible–infected–recovered model was applied to data of patients with symptoms in Japan during January 14 through March 26. The respective reproduction numbers for periods before VECSC (R0), during VECSC (Re), and after VECSC (Ra) were estimated. Results Results suggest R0 before VECSC as 2.534 [2.449, 2.598], Re during VECSC as 1.077 [0.948, 1.228], and Ra after VECSC as 4.455 [3.615, 5.255]. Discussion and conclusion Results demonstrated that VECSC can reduce COVID-19 infectiousness considerably, but after VECSC, the value of the reproduction number rose to exceed 4.0.

BackgroundCOCOA, a contact reporting application in Japan, was launched at the end of June 2020.ObjectWe assessed effectiveness of COCOA.MethodAfter developing a simple susceptible–infected–recovery model with COCOA and voluntary restrictions against going out (VRG), we assumed that COCOA can reduce infectiousness by 10–50% points through self-quarantine at home after receiving notification from COCOA.ResultsCOCOA alone is insufficient to halt an outbreak. Even if the entire population were to use COCOA, the reproduction number would be 1.31. However, if VRG were 15%, about half of the maximum VRG effectiveness under the emergency state declaration, then 10% COCOA use by a population can reduce the reproduction number to less than one.ConclusionSignificant effects of COCOA for reducing the reproduction number were found. However, without VRG, COCOA alone is insufficient to control an outbreak.

BACKGROUND In Japan, as a countermeasure against the COVID-19 outbreak, both the national and local governments issued voluntary restrictions against going out from residences at the end of March 2020 in preference to the lockdowns instituted in European and North American countries. The effect of such measures can be studied with mobility data, such as data which is generated by counting the number of requests made to Apple Maps for directions in select countries/regions, sub-regions, and cities. OBJECTIVE We investigate the associations of mobility data provided by Apple Inc and an estimate an an effective reproduction number R(t). METHODS We regressed R(t) on a polynomial function of daily Apple data, estimated using the whole period, and analyzed subperiods delimited by March 10, 2020. RESULTS In the estimation results, R(t) was 1.72 when voluntary restrictions against going out ceased and mobility reverted to a normal level. However, the critical level of reducing R(t) to CONCLUSIONS We demonstrated that Apple mobility data are useful for short-term prediction of R(t). The results indicate that the number of trips should decrease by 10% until herd immunity is achieved and that higher voluntary restrictions against going out might not be necessary for avoiding a re-emergence of the outbreak.

BackgroundIn Japan, as a measure to inhibit the COVID-19 outbreak, voluntary restrictions against going out (VRG) have been applied.ObjectMobility information provided by Apple Inc. and NTT Docomo were assessed in terms of its usefulness in predicting conditions exacerbating an outbreak.MethodA polynomial function was applied to daily Apple and Docomo data to calculate the observed R(t).ResultsThe correlation coefficient among Apple and Docomo data was 0.91. The adjusted coefficient of determination for R(t) for the whole study period was higher using Docomo data than when Apple data were used. When we regressed R(t) on daily Apple and Docomo data simultaneously, the estimated coefficient of Docomo data was not significant.Discussion and ConclusionWe demonstrated that Apple mobility data might be superior to Docomo data for explaining the entire course of the COVID-19 outbreak in Japan.

BackgroundIn Japan, as a countermeasure against the COVID-19 outbreak, voluntary restrictions against going out (VRG) have been applied.ObjectWe examined mobility information provided by Apple Inc. to a susceptible–infected–recovery model.MethodWhen applying a polynomial function to daily Apple data with the SIR model, we presumed the function up to a cubic term as in our earlier study.ResultsEstimation results demonstrated R0as 1.507 and its 95% confidence interval was [1.502, 1.509].. The estimated coefficients of Apple data was 1.748 and its 95% confidence interval was [1.731, 1.788].Discussion and ConclusionResults show that mobility data from Apple Inc. can explain the entire course of the outbreak in COVID-19 in Japan. Therefore, monitoring Apple data might be sufficient to adjust control measures to maintain an effective reproduction number of less than one.

BackgroundJapan’s Prime Minister Abe declared an emergency to control the COVID-19 outbreak on April 7, 2020. He asked almost half of the population of Japan to reduce their personal contacts by 70–80%.ObjectThis study estimates the effectiveness of that emergency declaration. Method: We applied a simple susceptible–infected–recovery model to data of patients with symptoms in Tokyo, Japan for January 14 – April 21 as of April 22. We estimate the reproduction number in four periods: R0 before voluntary event cancellation and school closure (VECSC) which was introduced since February 27 to March 19, Rv during the VECSC, Ra after VECSC, and Re after the emergency declaration.ResultsResults suggest that the value of R0 was estimated as 1.267; its range was [1.214, 1.341]. However, Rv was estimated as 2.360 [1.844, 2.623]. Ra was estimated as 2.307 [2.035, 2.794] and Re was 0.462 [0.347, 0.514].Discussion and ConcussionOne must be reminded that these results reflect only those at two weeks after the emergency declaration. The reproduction number probably changed thereafter continuously.

ObjectThe COVID-19 outbreak emerged in late 2019 in China, expanding rapidly thereafter. Even in Japan, epidemiological linkage of transmission was probably lost already by February 18, 2020. From that time, it has been necessary to detect clusters using syndromic surveillance.MethodWe identified common symptoms of COVID-19 as fever and respiratory symptoms. Therefore, we constructed a model to predict the number of patients with antipyretic analgesics (AP) and multi-ingredient cold medications (MIC) controlling well-known pediatric infectious diseases including influenza or RS virus infection. To do so, we used the National Official Sentinel Surveillance for Infectious Diseases (NOSSID), even though NOSSID data are weekly data with 10 day delays, on average. The probability of a cluster with unknown febrile disease with respiratory symptoms is a product of the probabilities of aberrations in AP and MIC, which is defined as one minus the probability of the number of patients prescribed a certain type of drug in PS compared to the number predicted using a model. This analysis was conducted prospectively in 2020 using data from October 1, 2010 through 2019 by prefecture and by age-class.ResultsThe probability of unknown febrile disease with respiratory symptom cluster was estimated as less than 60% in 2020.DiscussionThe most severe limitation of the present study is that the proposed model cannot be validated. A large outbreak of an unknown febrile disease with respiratory symptoms must be experienced, at which time, practitioners will have to “wing it”. We expect that no actual cluster of unknown febrile disease with respiratory symptoms will occur, but if it should occur, we hope to detect it.

BackgroundThe number of patients of COVID-19 in Tokyo has been increasing gradually through the end of March, 2020.ObjectSupport for policymaking requires forecasting of the entire course and outcome of the outbreak if a self-restraint in going out is not initiated. Moreover, the effects of a self-restraint in going out must be considered when choosing to initiate one. Method: Data of Tokyo patients with symptoms during January 14 – March 28, 2020 were used to formulate a susceptible–infected–recovered (SIR) model using three age classes and to estimate the basic reproduction number (R0). Based on the estimated R0, We inferred outbreak outcomes and medical burden if a self-restraint in going out were not enacted. Then we estimate the self-restraint in going out effects.ResultsResults suggest R0 as 2.86, with a 95% confidence interval of [2.73, 2.97]. Exhaustion of medical resources can be expected to occur on April 26 if no self-restraint in going out occurs. If a self-restraint in going out were enacted from April 6, and if more than 60% of trips outside the home were restricted voluntarily, then medical care service could be maintained.Discussion and ConclusionThe estimated R0 was similar to that found from other studies conducted in China and Japan. Results demonstrate that a self-restraint in going out with reasonable cooperation of residents is required to maintain medical care.

BackgroundIncidence in children was much less than in adults during the COVID-19 outbreak. Sports and entertainment events were canceled (VEC) in Japan for two weeks during 26 February – 13 March. Most schools were closed (SC).ObjectWe construct a susceptible–infected–recovered model using three age classes and estimate the basic reproduction number (R0) and protection level among children simultaneously. Then we simulate SC and VEC effects.MethodWe used data of patients with symptoms in Japan during 14 January to assess SC and VEC introduction. Effects of SC and VEC were incorporated into the model through change in the contact pattern or frequencies among age classes.ResultsResults suggest R0 as 2.86 [95%CI of 2.73, 2.97]. The protection level was estimated as 0.4 [0.2, 0.7]. SC and VEC can reduce the total number of patients significantly, by 6–7%.Discussion and ConclusionThe estimated R0 was similar to that found from other studies in China and Japan. We found a significant protection level among children, and by effects of SC and VEC. Introduction

BackgroundTo control COVID-19 outbreak in Japan, sports and entertainment events were canceled in Japan for two weeks from 26 February to 11 March. It has been designated as voluntary event cancellation (VEC).ObjectThis study predicts the effectiveness of VEC enduring and after its implementation.MethodWe applied a simple susceptible–infected–recovery model to data of patients with symptoms in Japan during 14 January to VEC introduction and after VEC introduction to 8 March. We adjusted the reporting delay in the latest few days.ResultsResults suggest that the basic reproduction number, R0, before VEC introduced as 2.50 with a 95% confidence interval (CI) was [2.43, 2.55] and the effective reproduction number, Rv, after VEC introduced as 1. 88; its 95% CI was [1.68,2.02].Discussion and ConclusionResults demonstrated that VEC can reduce COVID-19 infectiousness by 35%, but R0 remains higher than one.

In Japan, some measles outbreaks were initiated by a tourist from oversea and foreign workers recently. Moreover, rubella outbreak emerged since July 2018 mainly in the South Kanto, and the outbreak is currently ongoing in 2019. It is important to maintain a high measles-rubella combined vaccine (MR) coverage for measles-rubella control. Vaccination coverage for the second dose of MR (MR2) is 90.8% in Tokyo in 2016, which was the third worst among all prefectures in Japan. The purpose of this study was to clarify determinant factors of vaccination coverage for MR2 in Tokyo. Data were obtained for 49 wards and cities in Tokyo in 2016. We regressed vaccination coverage of MR2 on the times of notification by mail, the proportion of households receiving welfare payments, and the proportion of non-Japanese elementary school students. In addition to the simplest specification, five factors were included separately as explanatory variables: the proportion of public health nurses; the ratio of the number of pediatric medical facilities to the number of preschool and elementary school children; the moving-in rate; the proportion of households with a single parent; and the proportion of households with husband and wife both working. Results show that a high proportion of households receiving welfare payments, notification by two or more letters, and moving-in rate or a lower proportion of non-Japanese elementary school students improve coverage. In conclusion, the health authorities can exert efforts to reduce burden of time spent for vaccination and provide sufficient information to improve coverage.

Introduction: The Infection Control Law in Japan does not cover monitoring of human metapneumovirus (HMPV). Therefore, its epidemiology is not well known. However, rapid diagnostic testing for this virus has been reimbursed by public health insurance in Japan since 2014. One case of acute encephalitis caused by HMPV was reported in April 2017 in Ibaraki. All schools in Ibaraki prefecture started to participate in the (Nursery) School Absenteeism Surveillance System ((N)SASSy) in 2009. All nursery schools started to use it in 2012. Methods: We specifically examine its seasonality and incidence by age. The study period extends from October 1, 2014 through May 31, 2017. Results: In total, (N)SASSy received 187 cases during the period. Spring and early summer were apparently the high season. The highest incidence was 36 cases in April 2015. The incidence among zero and one year olds was higher in 2017 than in the same season among 2014-2016. The necessary effort to download data from (N)SASSy, show these figures, and confirm the situation and background was a few minutes. Discussion: Rapid diagnostic testing for HMPV elucidated its epidemiology for the first time. Moreover, timely information sharing through (N)SASSy led the Ibaraki prefectural office to publish a reminder in July 2017 about the HMPV outbreak situation and to encourage precautions against it by nursery schools.

Objective: We present descriptive epidemiology of Mycoplasma infection using the (Nursery) School Absenteeism Surveillance System ((N)SASSy) in addition to national official sentinel surveillance for infectious diseases (NOSSID). It is expected to be helpful for early detection and response to outbreak of Mycoplasma infection and also to be useful for antimicrobial resistance measures. Method: The study period was 2010-2014 seasons. The study area was the whole of Ibaraki prefecture, Japan. NOSSID reports the number of patients with Mycoplasma pneumonia from 13 sentinel hospitals. We compare the number of patients and the incidence rate of NOSSID with the same information in (N)SASSy. Result: In NOSSID, the largest number of patients by age was 27 patients of one year old in 2012. (N)SASSy showed that the incidence rate in the elementary schools is high in 2011 and 2012. Especially, the second grade students were the highest. Discussion: Even though Mycoplasma infection is well known as a pediatric disease, we showed that second grade was the highest in incidence at first. Because (N)SASSy is timely and real-time information collection, evaluation and sharing countermeasures with (nursery) schools, public health centers, and physicians are useful for students and nursery school children, and communities. Conclusion: Because mycoplasma infection is common pediatric infectious diseases and because some patients rarely develop severe infections, we must prevent larger outbreaks. (N)SASSy can provide timely intervention at the initial phase of outbreak by monitoring situations in (nursery) schools and comparing data to baseline information.

Background Our earlier report reported that the (Nursery) School Absenteeism Surveillance System ((N)SASSy) can decrease numbers of patients. This study evaluates (N)SASSy's cost-effectiveness. Methods A social perspective is taken for economic evaluation. For simplicity, 8,000 yen is assumed for direct medical costs. We assume the home health care duration to be 6 days, with 30 000 yen as the indirect opportunity cost of family nursing. Benefit-cost ratios are used as indicators of cost-effectiveness. Results By multiplying the disease burden per patient by the reduced number of patients, the (N)SASSy effect was estimated as 206.9 billion yen, with 95% confidence interval of [67.3,346.6] billion yen. The total cost attributable to (N)SASSy throughout Japan is expected to be 2.63 billion yen. The benefit-cost ratio is expected to be approximately 60. Conclusions The estimated benefit-cost ratio is much higher than that for the routine immunization of children.

Infection control in nursery schools and schools is important for community health and the health of children. In Japan, caregivers of children or students usually report the absence due to illness to their attending nurseries or schools, including symptoms and diagnosed diseases. The (Nursery) School Absenteeism Surveillance System, (N)SASSy, covers about 60% of schools and 40% of nurseries in Japan. In this paper, we evaluated the benefits of (N)SASSy as an infection control measure by a public health center. Mito Public Health Center (MPHC) covers 58 nurseries and 186 schools, as of May 2015, and called the nurseries and/or schools to confirm the situation, in case of aberration detected through (N)SASSy. The outcome was defined as the proportion of cluster avoidance by advice from MPHC. A cluster was identified, when the number of patients at the same facility with the same symptom or diagnosed disease was greater than ten during the prior seven days. During the study period (April 2015-March 2016), MPHC advised 85 times, and clusters were avoided 82 times (96.5%). The proportion of cluster avoidance was 100% for fever, enterohemorrhagic Escherichia coli infection, respiratory syncytial virus infection, or streptococcal pharyngitis infection. The proportion of cluster avoidance for diarrhea, vomiting or gastroenteritis infection, mumps, hand-foot-mouth disease (HFMD), and influenza was 78.8, 50.0, 20.0, and 6.7%, respectively. In conclusion, advice from a public health center given by phone based on information from (N)SASSy will be helpful for reducing the number of clusters of infectious diseases, except for HFMD and influenza.

Objectives In Ibaraki Prefecture, all (nursery) schools have joined the (Nursery) School Absenteeism Surveillance System (hereafter denoted as (N)SASSy), which is operated by the Japan School Health Association to monitor the prevalence of infectious diseases, the early detection and response for outbreaks, and prevention of large outbreaks. Prefectural government officers also utilize it as a control measure for infectious diseases. In particular, when cases of measles or rubella are registered, (N)SASSy sends e-mails automatically to prefectural government officers to activate control measures. This paper summarizes administrative responses by prefectural government officers for measles or rubella cases using (N)SASSy and discusses the future challenges.Methods We summarized registration, detection, and first response data for measles or rubella cases in (N)SASSy and compared the number of detected and reported cases enforced by the Infectious Diseases Control Law from January 1, 2013 to December 31, 2014.Results The public health center questioned hospitals/clinics and (nursery) schools about all registered measles or rubella cases in (N)SASSy on the same day to check the entered information. In the past 2 years, there were 5 measles and 56 rubella cases in 2013 and 1 measles and 19 rubella cases in 2014 registered with (N)SASSy. All cases were checked and investigated by the public health center. Of all cases detected by (N)SASSy, 7 rubella cases in 2013 and 1 rubella case in 2014 were reported based on the law. No measles cases were reported in the 2 years. The results of investigations and laboratory tests were given as feedback to the (nursery) schools. If the case did not case definition determined by the law, we changed the status in (N)SASSy to suspected or discarded cases.Conclusion Since (N)SASSy assists prefectural government officers with earlier detection of and response for infectious diseases, it definitely contributes to infection control. Immediate feedback of the laboratory test results to the (nursery) schools was also useful to confirm cases of measles or rubella. As data entry in (nursery) schools is needed for stable operation and utilization of (N)SASSy, it is important that workshops for (N)SASSy are held for (nursery) school teachers every year to maintain accuracy. Our future challenges include the coordination among (nursery) schools, hospitals/clinics, and prefectural government and their applications for infection control.