An Introduction to the Japanese Immunization Program: Past, Present, and Future Perspectives.

In Japan, immunization is regulated by the Immunization Law, enacted shortly after World War II ended. It has been subsequently revised in response to social changes; however, after public health conditions improved, adverse events following immunization have received more public attention than the effectiveness of vaccination. This kind of public opinion had a major impact on the immunization program, leading to a so-called "vaccine gap" around a decade ago, that is, the less availability of vaccines for routine vaccination as compared with other countries. However, in recent years, several vaccines have been approved and are being routinely administered with the same schedule as in other countries. National immunization programs are influenced by various factors, such as cultures, customs, habits and ideas. This paper summarizes the status of immunization schedule and practices in Japan, process of policymaking, and possible future issues.

Comparison of Clinical Characteristics of Children Infected With Coronavirus Disease 2019 Between Omicron Variant BA.5 and BA.1/BA.2 in Japan.

BACKGROUND: The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants has dramatically altered the clinical profile of pediatric coronavirus disease 2019 (COVID-19). In Japan, we experienced a pandemic of omicron subvariant BA.1/BA.2 from January through June 2022. However, after the emergence of BA.5 in early July 2022, the number of children hospitalized with COVID-19 increased dramatically in Japan. METHODS: We collected data on monthly numbers of cases and clinical characteristics of hospitalized children with COVID-19 in 13 hospitals, the total number of pediatric COVID-19 cases, and COVID-19 vaccination rates in Niigata, Japan, for the period from January 2020 through August 2022. We compared clinical presentation during the periods of BA.1/BA.2 predominance (January-June 2022) and BA.5 predominance (July-August 2022) and estimated vaccine effectiveness (VE) against hospitalization during the BA.5-predominant period. RESULTS: Between January 1, 2020, and August 31, 2022, 49,387 children (19,085 children/100,000 population) were newly diagnosed as having COVID-19, and 393 were hospitalized for COVID-19. Hospitalization for febrile seizure, especially complex seizure, was significantly higher during BA.5 predominance than during BA.1/BA.2 predominance (27.9% vs. 7.0%, P < 0.01). VE against hospitalization during BA.5 predominance was estimated to be 75% (95% confidence interval, 48%-88%, P < 0.01). CONCLUSIONS: The emergence of BA.5 significantly affected children in Japan; the number with complex febrile seizure who required hospitalization was higher than during BA.1/BA.2 predominance. The COVID-19 vaccination rate in children must be increased to prevent hospitalization for COVID-19 and to prepare for current and future variant outbreaks.

Acute and Postacute Clinical Characteristics of Coronavirus Disease 2019 in Children in Japan.

BACKGROUND: The clinical features of coronavirus disease 2019 (COVID-19) in children have been changing because of the emergence and rapid spread of variants of concern (VOC). The increase in cases infected with VOC has brought concern with persistent symptoms after COVID-19 in children. This survey aimed to analyze the clinical manifestations and persistent symptoms of pediatric COVID-19 cases in Japan. METHODS: We analyzed the clinical manifestations of pediatric COVID-19 cases reported between February 2020 and April 2022 in Japan, using a dedicated database updated voluntarily by the members of the Japan Pediatric Society. Using the same database, we also analyzed persistent symptoms after COVID-19 in children who were diagnosed between February 2020 and November 2021. RESULTS: A total of 5411 and 1697 pediatric COVID-19 cases were included for analyzing clinical manifestations and persistent symptoms, respectively. During the Omicron variant predominant period, the percentage of patients with seizures increased to 13.4% and 7.4% in patient groups 1-4 and 5-11 years of age, respectively, compared with the pre-Delta (1.3%, 0.4%) or Delta period (3.1%, 0.0%). Persistent and present symptoms after 28 days of COVID-19 onset were reported in 55 (3.2%). CONCLUSIONS: Our survey showed that the rate of symptomatic pediatric COVID-19 cases increased gradually, especially during the Omicron variant predominant period, and a certain percentage of pediatric cases had persistent symptoms. Certain percentages of pediatric COVID-19 patients had severe complications or prolonged symptoms. Further studies are needed to follow such patients.

Decline in pediatric admission on an isolated island in the COVID-19 pandemic.

BACKGROUND: A decrease in pediatric hospitalizations during the COVID-19 pandemic has been reported worldwide; however, few studies have examined areas with a limited number of COVID-19 cases, where influenced by viral interference by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is minimum. METHODS: We conducted an epidemiological study of pediatric hospitalizations on Sado, an isolated island in Niigata, Japan, that was unique environment with few COVID-19 cases and reliable pediatric admissions monitoring. We compared numbers of monthly hospitalizations and associated diagnoses for the periods April 2016 to March 2020 (pre-pandemic period) and April 2020 to March 2021 (pandemic period). RESULTS: Data were analyzed for 1,144 and 128 patients in the pre-pandemic and pandemic periods, respectively. We observed only three adults and no pediatric COVID-19 cases during the pandemic period. The number of monthly admissions was significantly lower in the pandemic period (median [interquartile ranges (IQR)]: 11.0 [7.0-14.0]) than in the pre-pandemic period (23.0 [20.8-28.3]; P < 0.001). Similar decreases were observed for hospitalizations due to respiratory tract infection (P < 0.01), but not for asthma exacerbation (P = 0.15), and gastrointestinal tract infection (P = 0.33). CONCLUSIONS: Pediatric hospitalizations during the pandemic significantly decreased on an isolated Japanese island where COVID-19 was not endemic and all pediatric admissions were ascertainable. This observation highlights the impact of decreased travel and increased awareness of infection control measures on pediatric hospitalizations due to infectious diseases, not by the SARS-CoV-2 viral interference.

Household Secondary Transmission of the Severe Acute Respiratory Syndrome Coronavirus 2 Alpha Variant From a Community Cluster in a Nursery in Japan.

BACKGROUND: Spread of variants of concerns (VOCs) of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has led to an increase in children with coronavirus disease 2019 (COVID-19). In February 2021, clusters of the Alpha variant of SARS-CoV-2 started to be reported in Niigata, Japan, including a large nursery cluster. We investigated the transmission routes and household secondary attack rates (SARs) in this cluster. METHODS: Epidemiologic data related to a nursery cluster in Niigata, Japan, particularly child-origin and adult-origin SARs, were analyzed. VOCs were confirmed by whole-genome sequencing of virus from patients. RESULTS: In total, 42 persons (22 children and 20 adults) in the cluster were infected with the Alpha variant. In the nursery, 13 of 81 children (16.0%) and 4 of 24 teachers (16.7%) were infected. SARS-CoV-2 later spread to 25 persons (10 children and 15 adults) outside the nursery. Child-origin and adult-origin household SARs were 27.7% (13/47) and 47.0% (8/17) ( P = 0.11), respectively, which were higher than rates attributable to non-VOCs in previous studies. CONCLUSIONS: As compared with non-VOCs, the Alpha variant of SARS-CoV-2 exhibited high transmissibility among children and adults and may pose a high risk for household secondary transmission from SARS-CoV-2-infected children. Increased transmissibility of current or future VOCs could lead to greater transmission from children to adults or other children.

High rates of vaccine hesitancy among pregnant women during the coronavirus disease 2019 (COVID-19) pandemic in Japan.

This study aimed to 1) determine the prevalence and contents of vaccine hesitancy among pregnant women during the coronavirus disease 2019 (COVID-19) pandemic and 2) evaluate its association with maternal sociodemographic factors. A cross-sectional survey was conducted between August and December 2020 among pregnant women between 28 and 32 weeks of gestation who received antenatal care at four clinics and hospitals in Niigata City, Japan. Vaccine hesitancy was assessed using the Parent Attitudes about Childhood Vaccines survey, and associations between vaccine hesitancy and sociodemographic factors were analyzed. In total, 113/200 (56.5%) subjects responded to the survey. Overall, 46/113 (40.7%) pregnant women were resistant or hesitant to receive the vaccine. Women with vaccine hesitancy were more likely to fear adverse reactions (concern 79.6%, not concerned 15.9%, and not sure 4.4%), safety (concerned 69.0%, not concerned 23.9%, and not sure 7.1%), and efficacy (concerned 47.8%, not concerned 35.4%, and not sure 16.8%) compared to those without vaccine hesitancy (P < .01, < .01, and <.01, respectively). In the multivariate logistic regression analyses, primipara women had higher rates of vaccine hesitancy than multipara pregnant women (odds ratio: 2.38, P = .04). In conclusion, the prevalence of vaccine hesitancy among pregnant Japanese women, especially primipara women, was higher than that in other countries during the COVID-19 pandemic. Their major concerns were adverse reactions, safety, and the efficacy of childhood vaccines. Further strategies are needed to provide appropriate vaccine information to prevent vaccine-preventable diseases in both infants and children.

Introduction of the Japanese Society for Pediatric Infectious Diseases.

The Pediatric Infectious Disease Journal became an official English journal of the Japanese Society for Pediatric Infectious Diseases starting from 2022. Japanese Society for Pediatric Infectious Diseases, with a history of more than 50 years and more than 3200 members in Japan, would like to contribute to the enhancement of child health and well-being in the field of pediatric infectious diseases by collaborating academic societies and organizations worldwide through the Pediatric Infectious Disease Journal.

Changes in Exanthema Subitum Incidence and Patient Age Distribution During the COVID-19 Pandemic in Japan.

Incidences of community-acquired infectious diseases other than COVID-19 decreased during the coronavirus disease 2019 pandemic; however, exanthema subitum incidence before (2016-2019) and during the pandemic (2020) in Niigata, Japan, did not substantially differ, although the proportion of age less than 1-year-old was lower in 2020. These findings suggest that exanthema subitum is transmitted mainly among family members, not in the community.

Coronavirus Disease 2019 Cluster Originating in a Primary School Teachers' Room in Japan.

BACKGROUND: School closures are a subject of debate during the present coronavirus disease 2019 (COVID-19) pandemic. Because children are not the main driver of COVID-19 transmission in the community, school education must be prioritized in conjunction with appropriate infection prevention and control measures, as determined by local COVID-19 incidence. METHODS: We investigated the causes and transmission routes of a primary school cluster of COVID-19 that occurred during November and December 2020 in Niigata, Japan. RESULTS: In the cluster, the virus spread among teachers, then from teachers to students, and then to their family members. This primary school cluster comprised 26 infected patients and included teachers (13/33, 39%), students (9/211, 4%), and family members (4/65, 6%). The secondary attack rate from the 3 index teachers to the remaining 30 teachers was 33%; however, the rate to students was only 4%. Factors contributing to cluster formation include the fact that 2 of the index teachers continued working while symptomatic and that the environment and infection prevention measures in the teachers' room were inadequate. CONCLUSIONS: To open schools safely and without interruption, adequate measures to prevent COVID-19 infection in schools should be emphasized not only for children but also for teachers and their environment.

The clinical characteristics of pediatric coronavirus disease 2019 in 2020 in Japan.

BACKGROUND: The COVID-19 pandemic has affected the lives of people of all ages. Most reports on pediatric cases suggest that children experience fewer and milder symptoms than do adults. This is the first nationwide study in Japan focusing on pediatric cases reported by pediatricians, including cases with no or mild symptoms. METHODS: We analyzed the epidemiological and clinical characteristics and transmission patterns of 840 pediatric (<16 years old) COVID-19 cases reported between February and December 2020 in Japan, using a dedicated database which was maintained voluntarily by members of the Japan Pediatric Society. RESULTS: Almost half of the patients (47.7%) were asymptomatic, while most of the others presented mild symptoms. At the time of admission or first outpatient clinic visit, 84.0% of the cases were afebrile (<37.5°C). In total, 609 cases (72.5%) were exposed to COVID-19-positive household members. We analyzed the influence of nationwide school closures that were introduced in March 2020 on COVID-19 transmission routes among children in Japan. Transmission within households occurred most frequently, with no significant difference between the periods before and after declaring nationwide school closures (70.9% and 74.5%, respectively). CONCLUSIONS: COVID-19 symptoms in children are less severe than those in adults. School closure appeared to have a limited effect on transmission. Controlling household transmission from adult family members is the most important measure for prevention of COVID-19 among children.

Changes in childhood vaccination during the coronavirus disease 2019 pandemic in Japan.

BACKGROUND: The coronavirus disease 2019 (COVID-19) pandemic has greatly affected daily life. COVID-19 often causes asymptomatic or mild disease in children; however, delayed routine childhood immunization is a concern, as it could increase the risk of vaccine-preventable disease. No study has evaluated the status of childhood vaccinations in Japan during the COVID-19 pandemic. METHODS: This retrospective observational study evaluated the number of vaccine doses administered to children in 4 Japanese cities (2 cities in the Tokyo metropolitan area and 2 cities far from Tokyo) during the period from 2016 to 2020. Vaccine doses administered between January and September 2020 during the COVID-19 pandemic were compared, by month, with those given during 2016-2019. Age-stratified demographic data were collected to determine whether factors other than change in the child population over time affected vaccination trends. RESULTS: In all cities the decrease in vaccine doses administered was most apparent in March and April 2020, i.e., just before or coincident with the declaration of a nationwide COVID-19 emergency on April 7, 2020. The decrease started as early as February in the Tokyo metropolitan area. As child age increased, the decrease became more apparent. Before the lift of national emergency on May 25, catch-up of the vaccination was observed in all age groups in all cities. Vaccine doses persistently increased in older age groups but not in infants. The overall vaccination trends did not differ significantly among the 4 cities. CONCLUSIONS: The COVID-19 pandemic significantly affected routine childhood immunization in Japan. Thus, a nationwide electronic surveillance system and announcements for guardians to encourage timely routine immunization are warranted.

Changes and remaining challenges for the Japanese immunization program: Closing the vaccine gap.

The Japanese immunization program has made considerable progress since 2009: several new vaccines have been introduced and most are included in the National Immunization Program (NIP). In October 2020, the Japanese law on immunization was revised, which resulted in a few laudable achievements. First, rotavirus vaccines were added to the NIP, 10 years after their introduction, and noteworthy studies of vaccine effectiveness and the incidence of intussusception in Japanese children were published. Second, rules on vaccine intervals-which had been a longstanding concern-were withdrawn. In addition to this revision of the law, the Japanese version of the Vaccine Information Statement (VIS) was released by the Japan Pediatric Society in 2018. The VIS provides useful caregiver information on general immunization concepts and individual vaccines. Further challenges for the Japanese immunization program include (1) administering a booster dose of pertussis-containing vaccine to preschool children or teenagers, (2) reestablishing the active recommendation for human papilloma virus vaccines, (3) adding the mumps and influenza vaccines to the NIP, and (4) ensuring optimal dosing of seasonal influenza vaccines. During the current coronavirus disease 2019 (COVID-19) pandemic, vaccination rates among children have been decreasing in many countries. In Japan, vaccination rates have been stable in infants, but declining among toddlers and school-aged children, despite public awareness of the need for timely administration of vaccines during the pandemic. Clearly, further action is needed if we are to adequately protect children living in Japan from vaccine-preventable diseases.

Improving Hand Hygiene Adherence in Healthcare Workers Before Patient Contact: A Multimodal Intervention in Four Tertiary Care Hospitals in Japan.

BACKGROUND: Hand hygiene is key to preventing healthcare-associated infection and the spread of respiratory viruses like the novel coronavirus that causes COVID-19. Unfortunately, hand hygiene adherence of healthcare workers (HCWs) in Japan is suboptimal according to previous studies. OBJECTIVES: Our objectives were to evaluate hand hygiene adherence among physicians and nurses before touching hospitalized patients and to evaluate changes in hand hygiene adherence after a multimodal intervention was implemented. DESIGN, SETTING, AND PARTICIPANTS: We conducted a pre- and postintervention study with HCWs at four tertiary hospitals in Niigata, Japan. Hand hygiene observations were conducted from June to August 2018 (preintervention) and February to March 2019 (postintervention). INTERVENTION: The multimodal hand hygiene intervention recommended by the World Health Organization was tailored to each hospital and implemented from September 2018 to February 2019. MAIN OUTCOMES AND MEASURES: We observed hand hygiene adherence before touching patients in each hospital and compared rates before and after intervention. Intervention components were also evaluated. RESULTS: There were 2,018 patient observations preintervention and 1,630 postintervention. Overall, hand hygiene adherence improved from 453 of 2,018 preintervention observations (22.4%) to 548 of 1,630 postintervention observations (33.6%; P < .001). Rates improved more among nurses (13.9 percentage points) than among doctors (5.7 percentage points). Improvement varied among the hospitals: Hospital B (18.4 percentage points) was highest, followed by Hospitals D (11.4 percentage points), C (11.3 percentage points), and Hospital A (6.5 percentage points). CONCLUSIONS: A multimodal intervention improved hand hygiene adherence rates in physicians and nurses in Niigata, Japan; however, further improvement is necessary. Given the current suboptimal hand hygiene adherence rates in Japanese hospitals, the spread of COVID-19 within the hospital setting is a concern.