Despite the low overall burden, some sociodemographic groups such as those residing in urban prefectures, younger age groups, being unvaccinated, and individuals engaged in occupations such as long\term care workers, childcare workers, and food service workers had higher odds of past infection. Our study complemented and supported the routine surveillance activity to provide a better picture of the cumulative burden of COVID\19. CONFLICT OF INTEREST The authors declare no conflicts of interest. ETHICS STATEMENT The ethics committee of the National Institute of Infectious Diseases approved our study (NIID 1312). data, Japan has been affected much less by COVID\19 compared with other countries. To validate this, we aimed to estimate SARS\CoV\2 seroprevalence and examine sociodemographic factors associated with cumulative infection in Japan. Methods A population\based serial cross\sectional seroepidemiological investigation was conducted in five prefectures in December 2021 (pre\Omicron) and FebruaryCMarch 2022 (Omicron [BA.1/BA.2]\peak). Anti\nucleocapsid and anti\spike antibodies were measured to detect infection\induced and vaccine/infection\induced antibodies, respectively. Logistic regression was used to identify associations between various factors and past infection. Results Among 16?296 participants (median age: 53 [43C64] years), overall prevalence of infection\induced antibodies was 2.2% (95% CI: 1.9C2.5%) in December 2021 and 3.5% (95% CI: 3.1C3.9%) in FebruaryCMarch 2022. Factors associated with past infection included those residing in urban prefectures (Tokyo: aOR 3.37 [95% CI: 2.31C4.91], Osaka: aOR 3.23 [95% CI: 2.17C4.80]), older age groups (60s: aOR 0.47 [95% CI 0.29C0.74], 70s: aOR 0.41 [95% CI 0.24C0.70]), being vaccinated (twice: aOR 0.41 [95% CI: 0.28C0.61], three times: aOR 0.21 [95% CI: 0.12C0.36]), individuals engaged in occupations such as long\term LDE225 Diphosphate care workers (aOR: 3.13 [95% CI: 1.47C6.66]), childcare workers (aOR: 3.63 [95% CI: 1.60C8.24]), food service workers (aOR: 3.09 [95% CI: 1.50C6.35]), and history of household contact (aOR: 26.4 [95% CI: 20.0C34.8]) or non\household contact (aOR: 5.21 [95% CI:3.80C7.14]) in FebruaryCMarch 2022. Almost all vaccinated individuals (15?670/15?681) acquired binding antibodies with higher titers among booster dose recipients. Conclusions Before Omicron, the cumulative burden was >10 times lower in Japan (2.2%) compared with the US (33%), the UK (25%), or global estimates (45%), but most developed antibodies owing to vaccination. LDE225 Diphosphate Keywords: coronavirus disease LDE225 Diphosphate 2019 (COVID\19), humoral immunity, Japan, seroepidemiologic studies, severe acute respiratory syndrome coronavirus 2 (SARS\CoV\2), vaccines 1.?INTRODUCTION Coronavirus disease 2019 (COVID\19), caused by severe acute respiratory syndrome coronavirus 2 (SARS\CoV\2), has resulted in substantial LDE225 Diphosphate morbidity and mortality globally. 1 Because SARS\CoV\2 infection can be asymptomatic and some infections are missed due to underdiagnosis and underreporting, a seroprevalence study can complement routine surveillance Rabbit Polyclonal to RGAG1 to provide a better picture of the cumulative burden of COVID\19. Also, coupling with questionnaires regarding various exposures can elucidate sociodemographic factors associated with cumulative infection. Japan has experienced six waves of COVID\19 epidemics as of March 2022, with the first three waves due to the original SARS\CoV\2 strain, and the fourth, fifth, and sixth waves by its Alpha, Delta, and Omicron variants respectively (Figure?1). Population\based seroprevalence surveys have been conducted twice by the Ministry of Health, Labour and Welfare and the Research Institute of Tuberculosis since the beginning of the COVID\19 pandemic. Although these surveys were conducted partly via convenient sampling, even in Tokyo with one of the highest reported cases (both absolute numbers and per population) consistently LDE225 Diphosphate throughout the pandemic, the seroprevalence was extremely low in June 2020 (0.1%) after the first wave, and December 2020 (1.4%) at the beginning of the third wave. 2 , 3 Open in a separate window FIGURE 1 Number of reported COVID\19 cases since the beginning of the pandemic and COVID\19 vaccine rollout in Japan (data sources: Ministry of Health, Labour and Welfare, Japan [https://www.mhlw.go.jp/stf/covid\19/open\data.html] and Digital Agency, Japan [https://info.vrs.digital.go.jp/dashboard]) The rollout of the primary series of COVID\19 vaccines started in mid\February 2021. BNT162b2, mRNA\1273, and AZD1222 have been approved for use (with minimal use of AZD1222). 4 The primary series.

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